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A stimulant found naturally in the leaves, seeds or fruits of over 63 plant species worldwide especially coffee beans, tea leaves, cocoa beans (chocolate) and kola nuts (cola). Part of a group of compounds known as methylxanthines. Added to soft drinks, foods, and medicines.
Caffeine is an alkaloid. It is metabolized in the liver and the breakdown products of caffeine are excreted through the kidney. In women on oral contraceptives, the rate at which they clear caffeine from the body is considerably slower. Pregnancy reduces a woman's ability to process caffeine still further. The half life of caffeine in an adult is about 3 to 4 hours. In pregnancy, it is 18 hours. Exerts its effects through competitive antagonism of the Adenosine receptors which are widely distributed throughout the body, especially in the brain.
A cup of coffee has 100-250 milligrams of caffeine. Black tea brewed for 4 minutes has 40-100 milligrams. Green tea has one-third as much caffeine as black tea.
In doses of 100-200 mg. caffeine can increase alertness, relieve drowsiness and improve thinking. At doses of 250-700 mg/day, caffeine can cause anxiety, insomnia, nervousness, hypertension, and insomnia. Caffeine is a diuretic and increases urination. It can curiously enough make it more difficult to lose weight because it stimulates insulin secretion, which reduces serum glucose, which increases hunger. Caffeine can help relieve some headaches, so a number of over-the-counter and prescription pain relievers include it as an ingredient, usually with aspirin or another analgesic.


Hormone secreted by the thyroid gland which controls the levels of calcium and phosphorous in the blood.

Calcium channels

Calcium channels
(a) Voltage-dependent calcium channels
Large unit conductance (25pS). Activated by high membrane potentials. Inactivated slowly by Ca2+-dependent/voltage-dependent mechanisms. Predominant type in muscle cells; mediate contraction in cardiac and smooth muscle cells. Activated by Bay K-8644, CGP 28392. Blocked by verapamil, dihydropyridines, diltiazem. 
Intermediate unit conductance (12-20pS). Activated by high membrane potentials. Inactivated at membrane potentials more positive than -40mV. Mainly neuronal; control neurotransmitter release. Blocked by w-conotoxin. 
Intermediate unit conductance (10-12pS). Activated at moderately high membrane potentials. Inactivated very slowly at membrane potentials more positive than -40 mV. Mainly neuronal: control neurotransmitter release (with N-type). Blocked by funnel web spider toxin w-aga-IVA. 
Small unit conductance (8pS). Activated at relatively negative membrane potentials. Transient Ca2+ current. Determine frequency of action potential generation in neurones and cardiac muscle cells. 
Catterall, W.A. and Striessnig, J. (1992) Trends Pharmacol. Sci. 13, 256-262.
Spedding, M. and Paoletti, R. (1992) Pharmacol. Revs. 44, 363-376. 
(b) Receptor-operated calcium channels
Receptor activation, rather than membrane potential, is the main trigger for opening these channels. See Barnard, E.A. (1992), Trends Biochem. Sci. 17, 368-374. 
(c) Intracellularly-activated Ca2+-selective channels
These include:

  • Ca2+ release channels in the sarcoplasmic reticulum, which release calcium for smooth muscle contraction (sometimes called ryanodine receptors, since this compound can activate them)
  • Inositol-1,4,5-triphosphate (IP3) receptors. Activated by elevated intracellular levels of IP3 following stimulation of cell surface receptors. They are structurally similar to ryanodine receptors and also cause a release of intracellular calcium stores.

Taylor, C.W. and Marshall, I.C.B. (1992) Trends Biochem. Sci. 17, 403-407.


An intracellular protein to which calcium binds in its function as a second messenger in hormone action.


A unit of heat and a unit of food energy; Chemical energy in foods is expressed in calories (Cal).  In heat terms, it is the amount of heat required to raise the temperature of 1 gram of water by 10°C from 14.5°C to 15.5°C. This is the true calorie, sometimes referred to as a "small calorie". One calorie (cal) equals 4.19 Joule (J). A kilocalorie is equal to 1000 calories and, likewise, the term kilo-calorie is the amount of heat required to raise the temperature of 1000 grams of water by 10°C. The kilo-calorie unit has largely been replaced by the Joule (1 kcal = 4.18 kJ).
In nutrition terms, the word calorie is used instead of the more precise scientific term kilocalorie which represents the amount of energy required to raise the temperature of a liter of water one degree Centigrade at sea level. The common usage of the word calorie of food energy is understood to refer to a kilocalorie and actually represents, therefore, 1000 true calories of energy. A calorie is also known as cal, gram calorie, or small calorie. The USDA Nutrient Database for Standard Reference contains values for both kilocalories and kilojoules (1 kcal equals 4.184 kJ).

Caloric test

A test of vestibular function. Involves the induction of nystagmus by putting warm or cold water in the external auditory meatus.


An apparatus used to measure the amount of energy evolved or absorbed in a chemical or physical process.


The cyclic form of adenosine monophosphate.Used frequently as a second messenger in eukaryotics and in catabolite repression in prokaryotes.

Canal hearing aid (also known as “In the ear hearing aid”)

A hearing aid that fits mostly in the ear canal with a small part of extending into the concha. It has a case molded to the user's ear.

Canalized character

A character whose phenotype is kept within narrow boundaries even in the presence of disturbing environments or mutations.


The psychoactive chemical substances found in marijuana (Cannabis sativa).

Cancellous Screw

A screw designed for placement in cancellous bone. The pullout strength of a screw is proportional to the amount of metal-bone contact. Because cancellous bone is porous, threads for cancellous bone screws have to be longer than for cortical screws to achieve the same degree of metal-bone contact and thus have the same pullout strength as cortical screws.


Small tubing for insertion into a cavity or vessel. Generally used to remove fluid for sampling or to introduce fluids, gases or drugs.

Cap (in molecular biology)

All eukaryotes have at the 5' end of their messages a methylated guanine residue called a "cap", consisting of a 7-methylguanosine in 5'-5' triphosphate linkage with the first nucleotide of the mRNA. It is added in reverse polarity (i.e. 3'pMeG5'ppp5'NpNp3') to the 5' end of eukaryotic mRNA during transcription initiation (i.e., post-transcriptionally) and is not encoded in the DNA. The cap binds a cap binding protein and acts as an initial binding site for ribosomes during translation.


The separation of charge resulting in the storing of electrical energy across a space. In cells, membranes have capacitor properties contributing to the storage of electrochemical energy (ion gradients).
In an electrical circuit, a capacitor is a dvice that is capable of charge separation and the storage of electrical energy in the form of an electric charge.
This capacity to store charge, Qm (nC/cm2), for a given voltage difference, Vm (mV), across the capacitor, Cm (µF/cm2): Qm = Cm x Vm
In cells, membranes have capacitor properties contributing to the storage of electrochemical energy in the form of differences in ionic concentrations on the two sides of the membrane (see also Chemical potential). Membrane capacitance arises from the ability of membranes to function as thin insulators between two electrolytic conductors (namely, the extracellular and intracellular fluids respectively).
Since biological membranes are of similar uniform thickness, they can be described as having a specific membrane capacitance, Cm. In contrast to specific membrane resistance, specific membrane capacitance is remarkably uniform among different types of biological membranes, ranging from 1-2 µF/cm2.
The relation between the membrane ionic current density, Ic (nA/cm2), flowing into the membrane capacitance, the membrane potential, Vm (mV), and the specific membrane capacitance, Cm(µF/cm2) is given by: Ic = dQm / dt = Cm.dVm/dt


Change in mammalian sperm that occurs after exposure to female genital tract making the sperm competent to undergo the acrosome reaction. This change is necessary for penetration of the cumulus matrix and for fertilization. Numerous molecular changes in the sperm are associated with capacitation, but the extent to which each event causes sperm capacitation is uncertain.


a device that stores electric energy in the form of an electric charge.


The smallest of blood vessels, penetrates the tissues and consists of a single layer of endothelial cells that allows exchange between the blood and interstitial fluid. These are the main suppliers of nutrients (including oxygen) to tissue.

Capillary action

The movement of water or any liquid along a surface ; The tendency of liquids to move into or out of tiny, hairlike passages. The means by which liquid moves through the porous spaces in a solid, such as soil, plant roots, and the capillary blood vessels in our bodies due to the forces of adhesion, cohesion, and surface tension. Capillary action is essential in carrying substances and nutrients from one place to another in plants and animals. the tendency of liquids to move into or out of tiny, hairlike passages.

Capillary array

Gel-filled silica capillaries used to separate fragments for DNA sequencing. The small diameter of the capillaries permit the application of higher electric fields, providing high speed, high throughput separations that are significantly faster than traditional slab gels.


A protein coat that acts as a surface structure enclosing the genetic materials and enzymes of a virus; The protein "shell" of a free virus particle.Conical-shaped capsids made up of multimers of the capsid protein, CA, enclose the RNA genome of mature HIV-1 particles. The CA C-terminal domain (CTD) has a dimer arrangement that is retained in the assembled CA. An intermolecular CTD-CTD interface is critical for capsid stability.
The shape of a viral capsid is rod-shaped, helical, polyhedral or icosahedral. 
Some viruses also contain an envelope surrounding the capsid.

Cap site

In eukaryotes, the cap site is the position in the gene at which transcription starts, and really should be called the "transcription initiation site". The first nucleotide is transcribed from this site to start the nascent RNA chain. That nucleotide becomes the 5' end of the chain, and thus the nucleotide to which the cap structure is attached (see "Cap"). In bacteria, the CAP site (note the capital letters) is a site on the DNA to which a protein factor (the Catabolite Activated Protein) binds.


Protein clusters making up discrete subunits of a viral protein shell.


A slimy layer around the cells of certain bacteria


Enzyme that breaks down certain disaccharides into monosaccharides.


A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides.Biochemical name for sugar containing molecules including single sugar (monosaccharides) like glucose and galactose, but also polysaccharides (complex carbohydrates) like starch (poly-glucose), cellulose (plant fiber material, also poly-glucose with a different chemical bond structure linking glucose units than those found in starch/glycogen and enzymatically indigestible by humans), chitin (hard shells of insects), and more complex carbohydrate components part of lipids and proteins such as blood serum glycoproteins (antibodies and blood group determinants A, O, B, rhesus positive or negative). All microorganisms (bacteria, viruses) contain carbohydrate surfaces (glycolipids) being the major determinants of immunogenic reactions during infections.


The element that defines the chemical properties of all life.All molecules that contain carbon are known as organic molecules and studies by organic chemistry. Carbon is the third most common element in cells, after hydrogen and oxygen, which are the most common biological elements because they are found in water. Also water makes up to 70% of a cells weight, it is not an organic molecule, since it lacks carbon.


- a heavy colorless gas that does not support combustion, dissolves in water to form carbonic acid, is formed in animal respiration and in the decay or combustion of animal and vegetable matter, and is absorbed from the air by plants in photosynthesis.

Carbonyl group

A functional group present in aldehydes and ketones, consisting of a carbon atom double-bonded to an oxygen atom.

Carboxyl group

A functional group founding organic acids, consisting of a single carbon atom double-bonded to an oxygen and single-bonded to a hydroxyl group (OH).


An agent (chemical or radiation) that causes cancer.


Tumour arising from epithelial tissue (eg glands; breast; skin; linings of the urogenital, intestinal and respiratory systems).

Cardiac cycle

The sequence of contraction and relaxation that makes up the heartbeat.

Cardiac muscle

A type of muscle that forms the contractile wall of the heart; its cells are joined by intercalated discs that relay each heartbeat.

Cardiac output

The volume of blood pumped by the heart in 1 minute

Cardiac scan

Using a radioactive element to create an image of the heart showing uptake of radioactivity in various areas. Very low doses are used that are imaged by very sensitive, sophisticated detectors. Cardiac scans can identify areas of damaged or dead tissue, or reduced metabolism due to reduced or blocked blood flow.


A diseased state of the heart involving abnormalities of the muscle fibers.
It is considered a primary problem when it occurs because the muscle cells themselves are abnormal (usually due to a gene mutation). It is a secondary problem when the muscle cells were normal but are affected by other diseases that have secondary damaging effects on the heart and its function such as certain infections, low blood flow to the heart, low blood oxygen or high blood pressure.The three main classes of cardiomyopathies are: Dilated cardiomyopathy, Hypertrophic cardiomyopathy, and Restrictive myopathy. There are also other, miscellaneous rare cardiomyopathies.
Dilated or congestive cardiomyopathy (DCM) is diagnosed when the heart is enlarged (dilated) and the pumping chambers contract poorly (usually left side worse than right).
Hypertrophic cardiomyopathy (HCM) is the second most common form of heart muscle disease, is usually genetically transmitted, and comprises about 35–40% of cardiomyopathies in children.
Restrictive cardiomyopathy (RCM) is a rare form of heart muscle disease that is characterized by restrictive filling of the ventricles. In this disease the contractile function (squeeze) of the heart and wall thicknesses are usually normal, but the relaxation or filling phase of the heart is very abnormal.

Cardiovascular system

A closed circulatory system with a heart and branching network of arteries, capilleries, and veins.


An animal, such as a shark, hawk, or spider, that eats other animals.
Hence: Carnivory = the consumption of living animal flesh.


Yellow, orange and red pigments in plants, often masked by chlorophyll and thought to function as protective antioxidants.

Carotid rete

A configuration of blood vessels in the brain that cools the brain.

Carrying capacity

The maximum population size that can be supported by the available resources, symbolized as K.

Cartesian coordinates

A system whereby points on a plane are identified by an ordered pair of numbers, representing the distances to two or three perpendicular axes.


A supportive flexible connective tissue consisting of chondrocytes embedded in chondrin (collagen and proteoglycans).


A sequence of successive activation reactions involving enzymes (enzyme cascade) or hormones (hormone cascade) characterized by a series of amplifications of an initial stimulus. In blood coagulation, for example, each enzyme activates the next until the final product, the fibrin clot, is reached.


A type of enzyme known as proteases, which play essential roles in apoptosis (cell death) and inflammation.
Caspases are characterized by their unusual ability to cleave proteins at specific sites. Active caspases can often activate other caspases, leading to a cascade of protein degradation.
As proteases, they are enzymes that cleave (cut) other proteins. They are called cysteine proteases, because they use a cysteine residue to cut those proteins, and called caspases because the cysteine residue cleaves their substrate proteins at the aspartic acid residue.
Caspases are essential in cells for apoptosis, one of the main types of programmed cell death in development and most other stages of adult life, and have been termed "executioner" proteins for their roles in the cell. Some caspases are also required in the immune system for the maturation of cytokines. Failure of apoptosis is one of the main contributions to tumour development and autoimmune diseases; this coupled with the unwanted apoptosis that occurs with ischaemia or Alzheimer's disease, has boomed the interest in caspases as potential therapeutic targets since they were discovered in the mid 1990s.
Eleven caspases have so far been identified in humans. There are two types of apoptotic caspases: initiator (apical) caspases and effector (executioner) caspases.
Initiator caspases (e.g. CASP2CASP8CASP9 and CASP10 cleave inactive pro-forms of effector caspases, thereby activating them.
Effector caspases (e.g. CASP3CASP6CASP7 in turn cleave other protein substrates within the cell resulting in the apoptotic process. The initiation of this cascade reaction is regulated by caspase inhibitors.
CASP4 and CASP5, which are overexpressed in some cases of vitiligo and associated autoimmune diseases caused by NALP1 variants, are not currently classified as initiator or effector in Mesh. This is because they are inflammatory caspases, which in concert with CASP1, are involved in cytokine maturation. CASP14, is not involved in apoptosis or inflammation, but instead is involved in skin cell development.
Caspases are regulated at a post-translational level, ensuring that they can be rapidly activated. They are first synthesized as inactive pro-caspases, that consist of a prodomain, a small subunit and a large subunit. Initiator caspases possess a longer prodomain than the effector caspases, whose prodomain is very small. The prodomain of the initiator caspases contain domains such as a CARD domain (e.g. caspases-2 and -9) or a death effector domain (DED) (caspases-8 and -10) that enables the caspases to interact with other molecules that regulate their activation. These molecules respond to stimuli which cause the clustering of the initiator caspases. This allows them to autoactivate, so that they can then proceed to activate the effector caspases.
The caspase cascade can be activated by : Granzyme B (released by cytotoxic T lymphocytes) which is known to activate caspase-3 and -7; death receptors (like FAS, TRAIL receptors and TNF receptor) which can activate caspase-8 and -10; the apoptosome (regulated by cytochrome c and the Bcl-2 family) which activates caspase-9.
Some of the final targets of caspases include: nuclear lamins, ICAD/DFF45 (Inhibitor of Caspase Activated DNase or DNA Fragmentation Factor 45), PARP (Poly(ADP) Ribose Polymerase), and PAK2 (P21-Activated Kinase 2).
The exact contribution that the cleavage of many caspase substrates makes to the biochemistry and morphology of apoptosis is unclear. However, the function of ICAD/DFF45 is to restrain the enzyme CAD (Caspase Activated DNase). The cleavage and inactivation of ICAD/DFF45 by a caspase allows CAD to enter the nucleus and fragment the DNA, causing the characteristic 'DNA ladder' seen in apoptotic cells.


A "package" of genetic material (containing more than one gene) that is inserted into the genome of a cell via gene splicing techniques. May include promoter(s), leader sequence, termination codon, etc.

Catabolic pathway

A metabolic pathway that releases energy by breaking down complex molecules into simpler compounds.

Catabolic reactions

Reactions in cells in which existing chemical bonds are broken and molecules are broken down.Generally these reactions produce energy, involve oxidation, and lead to a decrease in atomic order. Hence catabolism = Metabolic degradation reactions, which release energy.


Within a cell or organism, the sum of all chemical reactions in which large molecules are broken down into smaller parts. The part of metabolism responsible for degradation of nutrients and energy extraction for the benefit of ATP production.

Catabolite activator protein(CAP)

A protein that when bound with cyclic AMP (cAMP) can attach to sites on sugar-metabolizing operons to enhance transcription of these operons. In E. coli, a helper protein that stimulates gene expression by binding within the promoter region of an operon and enhancing the promoter's ability to associate with RNA polymerase.

Catabolite repression

Repression (inactivation) of certain sugar-metabolizing operons (e.g. lac) in favour of glucose utilization when glucose is the predominant carbon source in the environment of the cell.


Compound that speeds up or facilitates a reaction, by lowering the ctivation energy of a chemical reaction by forming a temporary association with the reacting molecules, without being altered in the process. Hence catalytic potential = The ability of a substance to increases the rate of a chemical reaction without itself being permanently changed.

Catalytic or autocatalytic RNA (also known as Ribozyme)

RNA with enzymatic activity, for instance, self-splicing RNA molecules in Tetrahymena.


A clouding of the eye lens, which becomes opaque resulting in visual problems.

Catarrhal deafness

Hearing loss resulting from inflammation of the mucous membrane of the air passages in the head and throat, with congestion of the Eustachian tube.

CAT (chloramphenicol acetyl transferase) assay

An enzyme assay. Chloramphenicol acetyl transferase is a bacterial enzyme which inactivates chloramphenicol by acetylating it. CAT assays are often performed to test the function of a promoter. The gene coding for CAT is linked onto a promoter (transcription control region) from another gene, and the construct is "transfected" into cultured cells. The amount of CAT enzyme produced is taken to indicate the transcriptional activity of the promoter (relative to other promoters which must be tested in parallel). It is easier to perform a CAT assay than it is to do a Northern blot, so CAT assays were a common method for testing the effects of sequence changes on promoter function. Largely supplanted by the reporter gene luciferase.

Catatonic behaviour

Marked motor anomalies, generally limited to disturbances in the context of a diagnosis of a non-organic psychotic disorder.

Catatonic excitement

A psychotic disorder behavior characterized by excited motor activity, apparently purposeless and not influenced by external stimuli.

Catatonic negativism

A psychotic disorder behavior characterized by an apparently motiveless resistance to all instructions or attempts to be moved. When passive, the person may resist any effort to be moved; when active, he or she may do the opposite of what is asked - for example, firmly clench jaws when asked to open mouth.

Catatonic posturing

A psychotic disorder behavior characterized by the voluntary
assumption of an inappropriate or bizarre posture, usually held for a long period of time.Example: A patient may stand with arms outstretched as if he were Jesus on the cross.

Catatonic schizophrenia

A marked psychomotor disturbance that may involve particular forms of stupor, rigidity, excitement or posturing. Sometimes when there is a rapid, alternation between the extremes of excitement and stupor, associated features include negativism, stereotypy and waxy flexibility. Mutism is common.

Catatonic stupor

A psychotic disorder behavior characterized by a marked decrease
in reactivity to environment and reduction in spontaneous movements and activity,
sometimes to the point of appearing to be unaware of one's surroundings.

Catatonic waxy flexibility

A type of psychotic disorder behavior in which a person's limbs can be "molded" into any position, which is then maintained. When the limb is being moved, it feels to the examiner as if it were made of pliable wax.


Type of flavonoid found in tea. May provide the health benefits of neutralizing free radicals and possibly reducing the risk of cancer


In a hierarchical classification system, the level at which a particular group is ranked.

Category scale

Items are placed in categories according to particular attributes, which can be verbally or numerically subdivided.


A hollow and flexible plastic tube that can be placed in a blood vessel for administration of solutions, collection of blood samples, or measurement of pressure.
Frequently used to drain the urinary bladder (Foley catheter).


A negatively charged electrode.


A positively charged ion, which has more protons than electrons.

Cation exchange

A process in which positively charged minerals are made available to a plant when hydrogen ions in the soil displace mineral ions from the clay particles.

Cauda equina

Meaning “horses tail”; a bundle of spinal nerves at the base of the spinal cord. The descending ventral and dorsal roots of the lumbar sacral and coccygeal nerves that lie in the subarachnoid space at the caudal tip of the spinal cord.

Caude equina syndrome

Impairment of the nerves in the cauda equina , the bundle of spinal nerve roots that arise from the lower end of the spinal cord . The syndrome is characterized by dull pain in the lower back and upper buttocks and lack of feeling ( analgesia ) in the buttocks, genitalia and thigh, together with disturbances of bowel and bladder function.

Caudate nucleus

A brain structure within the basal ganglia of the brain. Responsible for regulating and organizing information being sent to the frontal lobes from other areas of the brain. The name caudate is given because it is a tail-shaped mass of neuron cell bodies.


A burning pain due to injury of a peripheral nerve.


A cause and effect relationship. The causality of two events describes to what extent one event is caused by the other. When there is causality, there is a measure of predictability between the two events.

CCAAT box (CAT box, CAAT box, other variants)

An invariant DNA sequence at about minus 70 base pairs from the origin of transcription in many eukaryotic promoters. A sequence found in the 5' flanking region of certain genes which is necessary for efficient expression. A transcription factor (CCAAT-binding protein, CBP) binds to this site.

CD4 protein

An adhesion molecule (protein) imbedded in the outer wall (envelope) of human immune system and brain cells that functions as the receptor (door to entry into the cell) for the HIV (AIDS) virus. The gp120 envelope glycoprotein of the HIV (i.e., AIDS virus) directly interacts with the CD4 protein on the surface of helper T cells to enable the virus to invade the helper T cells.

CD44 protein

One of the adhesion molecules (embedded in the surface of the linings of blood vessels) that assists the neutrophils on their journey from the bloodstream through the walls of blood vessels (e.g., to combat pathogens into adjacent tissues).Tumor cells also exploit CD44 molecules in order to metastasize (spread throughout the body's tissue from a single beginning tumor) via a similar (tumor cell)-through-blood vessel- wall adhesion molecule mechanism.

cDNA (complementary DNA)

A stretch of DNA which faithfully copies a particular stretch of messenger RNA (i.e., it complements the mRNA); DNA that is synthesized from a messenger RNA template. DNA copies synthesized from a messenger RNA template using the enzyme reverse transcriptase; the single-stranded copy is often used as a probe to identify complementary sequences in DNA fragments or genes of interest. The single-stranded form is often used as a probe in physical mapping.
cDNA library = A pool of complementary DNA clones produced by cDNA cloning of total messenger RNA from a single source (cell type, tissue, embryo).

cDNA clone

cDNA is a piece of DNA copied from an mRNA.The term "clone" indicates that this cDNA has been spliced into a plasmid or other vector in order to propagate it.A cDNA clone may contain DNA copies of such typical mRNA regions as coding sequence, 5'-untranslated region, 3' untranslated region or poly(A) tail. No introns will be present, nor any promoter sequences (or other 5' or 3' flanking regions). A "full-length" cDNA clone is one which contains all of the mRNA sequence from nucleotide #1 through to the poly(A) tail.


Compact Disk Read Only Memory. A storage medium. Data are "stamped" onto the disk during the manufacturing process. The disk is read-only.


Fundamental structural unit of all life; Smallest unit of life (single cell organism or bacteria) or unit of higher organisms, i.e., multicellular organisms. The cell consists primarily of an outer plasma membrane (and cell wall in bacteria and plants = a membrane plus some chemically more stable structures, often mixtures of proteins and polysaccharides), which separates it from the environment; the genetic material (DNA), which encodes heritable information for the maintainance of life; and the cytoplasm, a heterogeneous assemblage of ions, molecules, and fluid and contain all necessary elements to sustain life; proteins, nucleic acids, lipids, minerals, and a diverse class of metabolites.. Cells of higher organisms (known as eukaryotes) are subdivided into subcellular compartments called organelles such as the mitochondrion, the cell nucleus, the endoplasmatic reticulum, the Golgi apparatus and many smaller organelles with highly specialized functions. While all these organelles are found in animal cells, plant cells in addition contain a central vacuole that controls pressure to stabilize the cell and chloroplasts, the site of photosynthesis or light depended biosynthesis of sugars (carbohydrates).

Cell autonomous

A genetic trait in multicellular organisms in which only genotypically mutant cells exhibit the mutant phenotype. Conversely, a nonautonomous trait is one in which genotypically mutant cells cause other cells (regardless of their genotype) to exhibit a mutant phenotype.

Cell-based therapies

Treatment in which stem cells are induced to differentiate into the specific cell type required to repair damaged or destroyed cells or tissues.

Cell centre

A region in the cytoplasm near the nucleus from which microtubules originate and radiate.

Cell culture

Growth of cells in vitro in an artificial medium.

Cell cycle

Complete sequence of steps which must be performed by a cell in order to replicate itself, as seen from mitotic event to mitotic event: The cycle of cell growth, replication of the genetic material and nuclear and cytoplasmic division.
An ordered sequence of events in the life of a dividing eukaryotic cell, composed of the M, G1, S, and G2 phases. Most of the cycle consists of a growth period in which the cell takes on mass and replicates its DNA. Arrest of the cell cycle is an important feature in the reproduction of many organisms, including humans.

Cell cycle control system

A cyclically operating set of proteins that triggers and coordinates events in the eukaryotic cell cycle

Cell fate

The ultimate differentiated state to which a cell has become committed.

Cell fractionation

The disruption of a cell and separation of its organelles by centrifugation.

Cell-free system

A mixture of cytoplasmic and/or nuclear components from cells and used for in vitro protein synthesis or transcription or DNA replication or other purposes.

Cell fusion

The formation of a hybrid cell produced by fusing two different cells.

Cell-mediated immunity  

Immune reaction directed against body cells that have been infected by viruses and bacteria; controlled by T cells.Also called Cellular Immune Response.
The immune response that is carried out by specialized cells, in contrast to the response carried out by soluble antibodies. The specialized cells that make up this group include cytotoxic T lymphocytes (CTL), helper T lymphocytes, macrophages, and monocytes. This system works in concert with the humoral immune response.
This type of immunity functions in defense against fungi, protists, bacteria, and viruses inside host cells and against tissue transplants.

Cell membrane

The outer membrane of a cell, which separates it from the environment. Also called a plasma membrane or plasmalemma.Acts as a selectively permable barrier to allows the cell to create an internal environment (cytoplasm) with a separate identitiy to the extracellular environment.

Cell plate

A double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis.

Cell theory

All living things are composed of cells; cells arise only from other cells. No exception has been found to these two principles since they were first proposed well over a century ago.

Cell transport systems

Mechanisms used to move substances across the cell membrane, which acts as a selectively permeable barrier to allow the cell to maintain an internal environment different from the external one.
There are three mechanisms:
1. Passive transport- no energy expenditure is required by the cell as the substrate moves down its thermodynamic potential (i.e., down its concentration gradient, from a region of High concentration to a region of Low concentration).  Passive transport systems are (a) Simple diffusion- no proteins (Osmosis is the special case of diffusion of water), and (b) Facilitated diffusion- carrier or channel protein is used to facilitate the movement of a solute.
2. Active transport- require energy (low to high).  There three active transport systems called (a) Ion pumps (or Ion ATPases), (b) ATP binding cassettes (ABC proteins or transporters), and (c) Group translocation which uses a sequence of molecules to transport a substance.
3. Ion-coupled (“indirect” or secondary active transport)-    no ATP directly (three types: uniport, symport, antiport)

Cellular automata

A simple mathematical system made of cells arranged on a grid; A program the applies a simple rule of what to do repeatedly.
Cells have a state; all states evolve simultaneously according to a uniform set of rules such that the state at step i+1 depends on the state in step i of the cell in question and of cells in a small neighbourhood. Depending on the rule of what to do next, the pattern or behavior generated can look (i) repetitive, simple, and symmetric, (ii) nested (fractal), (iii) random and without any symmetry or repetition whatsoever, or (iv) complex with local patterns but overall broken symmetry
Such a discrete dynamical system may serve to model physical systems; large cellular automata, despite their simplicity at the local level, can show behaviour of substantial complexity. As information processing systems, cellular automata may also be regarded as a subclass of artificial neural networks, in which node connections are of the nearest-neighbour type in two dimensions.

Cellular differentiation

The structural and functional divergence of cells as they become specialized during a multicellular organism's development; dependent on the control of gene expression.

Cellular respiration

The transfer of energy from various molecules to produce ATP.Occurs in the mitochondria of eukaryotes and in the cytoplasm of prokaryotes. In the process, oxygen is consumed and carbon dioxide is generated. The most prevalent and efficient catabolic pathway for the production of ATP


A structural polysaccharide of cell walls, consisting of glucose monomers joined by (1-4) glycosidic linkages.

Cell wall

A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists. In the case of plant cells, the wall is formed of cellulose fibers embedded in a polysaccharide-protein matrix. Rigid structure deposited outside the cell membrane. The primary cell wall is thin and flexible, whereas the secondary cell wall is stronger and more rigid, and is the primary constituent of wood. Plants are known for their cell walls of cellulose, as are the green algae and certain protists, while fungi have cell walls of chitin.


a unit of measurement for temperature.   Water freezes at 0ºC (zero degrees Celsius) and boils at 100°C (100 degrees Celsius).

Celsius scale

A temperature scale (°C) equal to 5/9 (°F – 32) that measures the freezing point of water at 0°C and the boiling point of water at 100°C.

Centimorgan (cm)

A chromosome mapping unit; A unit of measure of recombination frequency.One centimorgan equals 1% recombinant offspring, i.e., equal to a 1% chance that a marker at one genetic locus will be separated from a marker at a second locus due to crossing over in a single generation. In human beings, 1 centimorgan is equivalent, on average, to 1 million base pairs.

Central angle

An angle that has its vertex at the center of a circle.

Central auditory processing disorder (CAPD)

See Auditory processing disorder (CAPD)

Central dogma

The original postulate that genetic information can be transferred only from nucleic acid to nucleic acid and from nucleic acid to protein, that is from DNA to DNA from DNA to RNA and from RNA to protein (although information transfer from RNA to DNA was not excluded and is now known to occur [reverse transcription]).
Transfer of genetic information from protein to nucleic acid never occurs.

Central limit theorem

This theorem states that the sum of a large number of random variables is approximately normally distributed, even though the random variables themselves may follow any distribution or be taken from different distributions. The only conditions are that the original random variables must have finite expectation and variance.Although the theorem is only true of an infinite number of variables, in practice the convergence to the Gaussian distribution is very fast. For example, the distribution of the sum of ten uniformly distributed random variables is already indistinguishable by eye from an exact Gaussian.

Central nervous system

In vertebrate animals, the brain and spinal cord.

Central pattern generators

Refer to networks of neurons in the spinal cord (and brainstem) that are capable of generating their own outputs to motorneurons independently of any descending or peripheral sensory input. CPGs are important in locomotion and respiration.

Central venous pressure (CVP)

Pressure within the superior vena cava, which reflects the pressure under which the blood is returned to the right atrium


The point that is the same distance from all the points on a circle.   The point that is the same distance from all the points on a sphere.   The point inside an ellipse where the major and the minor axes intersect.   The center of a circle that can be inscribed in a regular polygon.

Centre surround organization (in neuroscience: of the receptive field of a neuron)

A particular form of organization of the receptive field of a sensory neuron; generally a pattern of RF activity found in the visual system. The receptive field of the neuron describes the set of sensory receptors that elicit a response in the neuron. In the centre-surround pattern of organization of a RF, a stimulus at the centre of the neuron’s receptive field elicits one response (e.g. a depolarisation or 'on' centre response), while an annulus of light around it produces the opposite effect (e.g. a hyperpolarisation or 'off' surround response).


Separating molecules by size or density using centrifugal forces generated by a spinning rotor. Liquid samples are spun around at high speed to cause the accelerated settling of particles in suspension. G forces of several hundred thousand times gravity are generated in ultracentrifugation.


A structure in an animal cell, composed of cylinders of microtubule triplets arranged in a 9 + 0 pattern. An animal cell usually has a pair of centrioles, which are involved in cell division.A short cylindrical organelle, found in pairs arranged at right angles to each other at the centre of a microtubule organizing centre (MTOC) or centrosome, found in eukaryotes (except in higher plants). A centriole is similar in structure to the basal body found at the base of eukaryotic cilia and flagella and organises the axoneme, the bundle of microtubules and other proteins forming the core of each cilium or flagellum. The centrosome organizes formation of a spindle during mitosis or meiosis.


Synonymous with centre of gravity; Centre of mass of an object.The point where the object would balance if supported by a single support.   The point in a triangle where the three medians intersect. Most often used for two- (or more-) dimensional distributions, designating the point given by the arithmetic mean in all variables.


The constricted centralized region of a nuclear chromosome, to which the spindle fibres attach during division. A kinetochore.


The primary microtubule organising center (MTOC) of animal cells, that divides prior to cell division each daughter MTOC acts as one pole of the spindle apparatus.
Material present in the cytoplasm of all eukaryotic cells and important during cell division; also called microtubule-organizing center (MTOC). The centrosome usually contains a pair of centrioles.


The concentration of sensory tissues in the anterior part of the body (head).


Part of the vertebrate hindbrain (rhombencephalon) located dorsally. Contains more neurons than the cerebrum and functions in unconscious coordination of fine movement and balance; likely to play an important role in other functions.but these are yet to be elucidated. Damage may result in ataxia.

Cerebral cortex

The surface of the cerebrum; the largest and most complex part of the mammalian brain, containing sensory and motor nerve cell bodies of the cerebrum; the part of the vertebrate brain most changed through evolution.

Cerebral lupus

A chronic autoimmune disease characterized by inflammation in the brain.

Cerebral palsy

A condition caused by damage to the brain, usually occurring before, during or shortly following birth. Characterized by an inability to fully control motor function, general physical weakness, lack of coordination, and perceptual difficulties. Each characteristic can range from mild to severe.

Cerebrovascular accident (CVA)

A "stroke". Arises because of the bursting of a blood vessel in the brain causing internal bleeding or a clot arising in a brain blood vessel (a thrombus) or elsewhere (embolus) and travelling to get stuck in a brain vessel which then deprives brain tissue of oxygen.

Cerebrospinal fluid (CSF)

A clear, colorless, serum-like fluid that circulates through the ventricles and
subarachnoid spaces of the brain and around the spinal cord. Most of the CSF is produced in the lateral ventricles.CSF serves to protect the brain and spinal cord, acting as a “shock absorber”. Biochemical and pathological changes in the brain can alter the composition of this fluid.The CSF circulates from the lateral ventricles to the third and then fourth ventricles. From the fourth ventricle, most of the CSF passes into the subarachnoid space, a space within the meninges of the brain, although some CSF also passes into the central canal of the spinal cord. The CSF returns to the blood through the arachnoid villi located in the dural sinuses of the meninges.


The dorsal portion, composed of right and left hemispheres, of the vertebrate forebrain.Carried out a whole range of sensory and motor functions, as well as being the integrating center for memory, learning, emotions, and other highly complex functions of the central nervous system.


Having to do with any kind of neck including the neck on which the head is perched and the neck of the uterus. The word "cervix" in Latin means "neck". That is why cervical vertebrae and cervical cancer involve quite disparate parts of the anatomy joined only by the meaning of the word "cervix".

Cessation cassette

A three-gene cassette (genetic sequence construct) that, when inserted into a plant and when activated via tetracycline antibiotic, prevents the seeds produced by that plant from germinating.That is because the "cessation cassete" stops those resultant seeds from synthesizing a specific protein needed for seed germination.

Chain reaction

Polymerisation initiated by the bonding of a free radical with a monomer.

Channel (in data analysis or plots)

The measured value of a parameter, representing the signal intensity of an event after amplification. To appear on a plot, data for an event must fall into one of either 256 channels (0-255) or one of 1024 channels (0-1023) depending on the resolution of the plot.

Channel Ioin channel)

A membrane protein that allows the passive flow of ions across a cell membrane.
Ion channels are usually selective for a specific ion type (e.g. Na, or K, or Cl, or Ca) and or either open or closed. These are two main structural states of the protein (a third state is a refractory state, a special closed state) and the change from the open to the closed state (gating) is regulated by the cell. Several regulatory mechanisms have been described including voltage-gating, ligand-gating, heat, and mechano-sensation (touch sensitive). Channels are a category of transporters.


Heritable trait possessed by an organism, that can be used for recognizing, differentiating or classifying a taxon.Biologists use characters from a variety of different sources, including morphological, behaviorial, developmental, and molecular data. Characters are usually described in terms of their states, for example: "hair present" vs. "hair absent," where "hair" is the character, and "present" and "absent" are its states

Character displacement

A phenomenon in which species that live together in the same environment tend to diverge in those characteristics that overlap; exemplified by Darwin's finches.

Character encoding scheme

A method of encoding characters including alphabetic characters (A-Z, uppercase and lowercase), numbers 0-9, punctuation and other marks (e.g. comma, period, space, &, *), and various "control characters" (e.g., tab, carriage return, linefeed) using binary numbers .For a computer to, for instance, print a capital A or a number 7 on the computer screen, we must have a way of telling the computer that a particular group of bits represents an A or a 7. There are standards, commonly called "character sets," that establish that a particular byte stands for an A and a different byte stands for a 7. The two most common standards for representing characters in bytes are ASCII ASCII and EBCDIC.

Character format

Any file format in which information is encoded as characters using only a standard character encoding scheme . A file written in "character format" contains only those bytes that are prescribed in the encoding scheme as corresponding to the characters in the scheme (e.g., alphabetic and numeric characters, punctuation marks, and spaces. A file written in the ASCII character format, for instance, would store the number "7" in eight bits (i.e., one byte ): 00010111. A file written in EBCDIC EBCDIC would store the number "7" in eight bits as: 11110111. Contrast with binary format.

Character state

Alternative forms of a character, a heritable trait (in genetics).

Chargaff's rule

In the base composition of DNA the quantity of adenine equals the quantity of thymine and the quantity of guanine equals the quantity of cytosine.


The state of an atom that has gained or lost an electron.The amount of unbalanced electricity in a system.  Either positive or negative.

Charon phage

Phage lambda derivative used as vector in DNA cloning.


Substance that binds particular ions, removing them from solution, e.g., EDTA is a chelator of divalent cations such as Mg++.

Chemical bond  

An attraction between two atoms resulting from a sharing of outer-shell elctrons or the presence of opposite charges on the atoms; the bonded atoms gain complete outer electron shells.

Chemical equilibrium  

The condition when the forward and reverse reaction rates are equal and the concentrations of the products remain constant. In a reversible chemical reaction, the point at which the rate of the forward reaction equals the rate of the reverse reaction.

Chemical indicator system

System using calibrated chemical agents (one type of which changes colour as a function of time and temperature of exposure to heat) to determine whether a process cycle has met the specified requirements.
(See Biological indicator system)

Chemical inertness or Chemically inert substances

Substances or elements which do not react easily with any other substances or elements. Chemically inactive materials.

Chemical potential

The chemical potential of a substance, A, in
phase a, is symbolised as:

Its value is given by
the following expression:

Analogous to electrical potentials (where electrons will flow from a region of high electrical potential to one of low potential) and gravitational potentials (where objects placed in regions of high gravitational potential will fall towards regions of lower potential).

The same idea occurs in chemistry: molecules and/or ions will move from states of high chemical potential to states of low potential. (Note that when the chemical substance passes from the state of high chemical potential to a state of low potential energy, ‘free energy’, symbolized as DG, is made available to do work.)

For all biological calculations 

may be taken as

where C is the concentration of A in phase a.  From this comes the concept of concentration gradients with which students of biology are familiar in the context of movement of ions or other molecules across cell membranes.
(see also Capacitance)

Chemical reaction

A process leading to chemical changes in matter; involves the making and/or breaking of chemical bonds. The transformation of substances by the rearrangement of their atoms.


The production of light photons by a chemical or electrochemical reaction.
Chemiluminescence usually involves the oxidation of an organic compound such as luminol or acridinium esters by an oxidant such as hydrogen peroxide or hypochlorite. Chemiluminescent reactions occur in the presence of catalysts such as alkaline phosphatase, horseradish peroxidase, metal ions or metal complexes.


Computer software and hardware used in drug discovery and development programs for chemical screening and analysis.


The process by which ATP is produced in the inner membrane of a mitochondrion.
The electron transport system transfers protons from the inner compartment to the outer of themitochondrion; as the protons flow back to the inner compartment, the energy of their movement is used to add phosphate to ADP, forming ATP.
Thus the energy of hydrogen-ion gradients across membranes to phosphorylate ADP and produce ATP; powers most ATP synthesis in cells.

Chemiosmotic coupling

The mechanism by which ADP is phosphorylated to ATP in mitochondria and chloroplasts. The energy released as electrons pass down an electron transport chain is used to establish a proton gradient across an inner membrane of the organelle; when protons subsequently flow down this electrochemical gradient, the potential energy released is captured in the terminal phosphate bonds of ATP.


An organism that derives energy from chemicals in nonliving surroundings. An organism that needs only carbon dioxide as a carbon source but that obtains energy by oxidizing inorganic substances.


An organism that must consume organic molecules for both energy and carbon.


A receptor that transmits information about the total solute concentration in a solution or about individual kinds of molecules.


The biological synthesis of organic material using chemical reactions as an energy source. Microorganisms metabolically transform inorganic carbon to organic carbon (cells) using energy derived from oxidation of reduced compounds. Chemosynthesis is the basis for the food web associated with deep-sea hydrothermal vents.


Applied to autotrophic bacteria that use the energy released by specific inorganic reactions to power their life processes, including the synthesis of organic molecules.


A process whereby a cell or organism follows chemical signals (chemo-) to move toward (-taxis) or away from a desired target.Commonly used to describe the developmental process of a neuron when its growth cone follows chemical signals to move toward a desired target.


An organism that obtains energy by oxidising chemicals.


The area of the body located between the neck and the abdomen . The chest contains the lungs , the heart and part of the aorta . The walls of the chest are supported by the dorsal vertebrae , the ribs , and the sternum

Chest x-ray

Commonly used to detect abnormalities in the lungs, but can also detect abnormalities in the heart, aorta, and the bones of the thoracic area. Metallic objects, such as jewelry are removed from the chest and neck areas for a chest x-ray to avoid interference with x-ray penetration and improve accuracy of the interpretation.

Chest percussion

A technique in which the practitioner claps on the patient’s chest wall using a cupped hand to induce vibration throughout the lung parenchyma, facilitating bronchial secretion clearance. The technique may also be performed with the assistance of mechanical devices

Cheyne-Stokes breathing

A breathing pattern which begins with short shallow breaths, increase in depth and frequency, reach a peak and then taper off. A short or long pause may follow. Defined as l0 to 30 seconds of apnea, followed by a gradual increase in the volume and frequency of breathing, followed by a gradual decrease in the volume of breathing until another period of apnea occurs

Chiasma (plural = chiasmata) (in genetics)

A cross-shaped structure and/or a site where there is some physical cross over of structures.
In cell biology chiasmata are the site of crossing-over. They are the X-shaped configuration seen in tetrads during the latter stages of prophase 1 of meiosis  and are commonly observed between nonsister chromatids during meiosis. They represent physical crossovers between DNA molecules.
In vision, nerve fibres from the retinae of the two eyes travel into the brain towards its midline; then at the optic chiasm nerves fibres from the nasal half of each eye cross over to join the nerve fibres ofrom the temporal half of the opposite eye and run with those fibres to the visual cortex.

Chiasm (in vision)

The place in the brain at which nerves fibres from the nasal half of each eye cross over to join the nerve fibres ofrom the temporal half of the opposite eye and run with those fibres to the visual cortex.

Chimera  (or mosaic)

A tissue containing two or more genetically distinct cell types, or an individual composed of such tissues. Individual made up of two or more genetically distinct cell lines.


An experimental targeted repair process in which a desirable sequence of DNA is combined with RNA to form a chimeraplast. These molecules bind selectively to the target DNA. Once bound, the chimeraplast activates a naturally occurring gene-correcting mechanism. Does not use viral or other conventional gene-delivery vectors.

Chimeric figure

A figure made up of two separate faces on each half (e.g., the left half of one person’s face matched with the right half of another person’s face.)
These figures are used in split brain experiments.

Chimeric plasmid

Hybrid or genetically mixed plasmid used in DNA cloning.

Chiral compound

A compound that contains an asymmetric center (chiral atom or chiral center) and thus can occur in two nonsuperimposable mirror-image forms (enantiomers).

Chi site

Sequence of DNA at which the RecBCD protein cleaves one of the strands during recombination

Chi-square distribution

Chi square, or goodness of fit, distributions are a family of probability distributions of the Chi-Square statistic, one for each degree of freedom. For small degrees of freedom, the distribution is skewed to the right. As the number of degrees of freedom increases, the distribution rapidly becomes symmetrical. For large degrees of freedom, the chi square distribution closely approximates a gaussian curve.

Chi-square test

A statistical test used to determine the probability of obtaining the observed results by chance, under a specific hypothesis. A statistical test which computes the probability that there is no significant difference between the expected frequency of an occurrence with the observed frequency of that occurrence.


A chlorophyll-containing plastid found in algal and green plant cells; An organelle found in eukaryotic algae and plants (and occasionally as symbionts in certain protist and animal cells). The site of photosynthesis and of chlorophyll.


A family of pigments used in photosynthesis to trap radiant energy. Normally located with chloroplasts. Chloroplasts with chlorophyll b have a bright green colour, those with chlorophylls a and c are off-green or yellow.


A soft, waxy substance found among the fats in the bloodstream and in all the body's cells; Important lipid found only in animals. A steroid that forms an essential component of animal cell membranes, but also serves as a biosynthetic precursor molecule for the synthesis of other biologically important steroid hormones (e.g. sex hormones) and the active gall bladder ingredients bile acids (= detergents).  The human liver can synthesize all the necessary levels of cholesterol and will reduce its own synthesis if cholesterol is taken in during a meal (only from animal sources). 'Bad' and 'Good' cholesterol refers to special transport particles of lipids in our blood serum called lipoprotein particles. The low density form or LDL is high in cholesterol and chronically high concentration of LDL in blood results in insoluble deposits that can clog arteries and restrict blood flow contributing to heart problems.
Cholesterol can undergo various pathways that result in the synthesis of various steroids. It is also an important determinant oxf membrane fluidity, and an improper amount in the body can lead to membrane instability, which leads to cell death.


A protein-carbohydrate complex secreted by chondrocytes; chondrin and collagen fibers form cartilage.

Chondroitin Sulfate

Chondroitin sulfate is a chemical that is normally found in cartilage around joints in the body.
When used with conventional anti-inflammatory medications such as ibuprofen (Advil, Motrin, etc.), chondroitin sulfate seems to help reduce hip and knee joint pain due to a type of arthritis known as osteoarthritis. It can take up to 4 months of treatment for relief of pain.
Chondroitin sulfate is often sold in combination products that also contain glucosamine sulfate. So far, there is no evidence that the combination products work any better than either chondroitin sulfate or glucosamine sulfate alone. Buying a combination product is probably not worth any extra cost.
There isn’t enough information to know if chondroitin sulfate is effective for other conditions people use it for, including: heart disease, osteoporosis (weak bones), or high cholesterol.


A line segment that connects two points on a curve.


Organism having a notochord at some stage of development - a rigid cartilaginous rod in the back extending from anterior to posterior. A member of a diverse phylum of animals that possess a notochord; a dorsal, hollow nerve cord; pharyngeal gill slits; and a postanal tail as embryos. This group includes the vertebrates.


Basal ganglion disease characterized by rapid, complex, involuntary jerking movements of the skeletal muscles. Occurs especially for individual muscles or small muscle groups of the face, fingers and toes.


A form of cerebral palsy marked by variable muscle tone and involuntary movements of the arms and legs.


The outermost of the four extraembryonic membranes of amniotes; contributes to the formation of the mammalian placenta.It forms from the somatopleure (ectoderm and somatic mesoderm). In birds and reptiles, the membrane adheres to the shell and is highly vascularized to serve in gas exchange. In mammals, it forms the fetal contribution to the placenta, made by trophoblastic tissue and extraembryonic mesoderm, containing blood vessels that allow exchange of materials with maternal circulation

Chorionic somatomammotropin

Hormone that promotes maternal breast development during pregnancy.

Chorionic villus sampling (CVS)  

A technique for prenatal testing for diagnosing genetic and congenital defects while the fetus is in the uterus. Fetal cells from the fetal side of the placenta (chorionic villi) are extracted and analyzed for chromosomal and biochemical defects


A vascular membrane in the eye containing pigment cells, which lies between the retina and sclera.

Choroid plexus

A network of capillaries that projects into each brain ventricle, and the area where cerebrospinal fluid is produced. Ependymal cells (a type of neuroglial cell) surround these capillaries. Blood plasma entering the ependymal cells from the capillaries is filtered as it passes into the ventricle, forming CSF. The ependymal cells maintain a blood-CSF barrier controlling the composition of the CSF.


A strand of a replicated chromosome, which are joined at the centromere; consists of DNA and protein. One of the two side by side replicas produced by chromosome replication in mitosis or meiosis. Subunit of a chromosome after replication and prior to anaphase of meiosis II or mitosis. At anaphase of meiosis II or mitosis when the centromeres divide and the sister chromatids separate each chromatid becomes a chromosome.


A complex of DNA and protein in eukaryotic cells that is dispersed throughout the nucleus during interphase and condensed into chromosomes during meiosis and mitosis. The nucleoprotein material of the eukaryotic chromosome.
When the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope.

Chromatin Immunoprecipitation (ChIP)

A method for isolating and characterizing the specific pieces of DNA out of an entire genome, to which is bound a protein of interest.
The protein of interest could for example be a transcription factor, or a specific modified histone, or any other DNA binding protein. This procedure requires an antibody to that protein of interest. The chromosomal material is isolated with all the proteins still bound to the genomic DNA. After fragmenting the DNA, the antibody is used to immunoprecipitate all chunks that contain the protein of interest. Isolate the DNA from those chunks, and it is possible to characterize the specific DNA sites to which the protein was bound.
There are two common ways to characterize the DNA so isolated: ChIP-chip (or "ChIP-on-chip") or ChIP-seq.
ChIP-chip: In this variant, the DNA isolated from a ChIP experiment is characterized by labeling it with a fluorescent dye, then hybrizidizing it to a DNA array (an oligonucleotide array, for example). Array spots that "light up" are taken as evidence that their specific sequence is present in your ChIP product. Unfortunately, designing these arrays requires that you have some idea what to expect in your ChIP isolates.
ChIP-seq: A newer variant for characterizing ChIP results, one can simply sequence everything that immunoprecipitated with the antibody. It requires no fore-knowlege of the expected products, as would ChIP-chip.

Chromatin Remodeling

A re-shaping (at molecular scale) of chromatin (i.e., organism's complex of DNA and histone protein), that alters which specific genes in that organism's DNA subsequently get expressed.Can be caused by short interfering RNA (siRNA), certain transcription activators, acetylation of histone, methylation of histone, sumoylation of histone, etc.


A method of separating a mixture of compounds by the use of a porous material, generally arranged in a column.


A term used variously to refer to some or all of those algae with chloroplasts having chlorophylls a and c (i.e. stramenopiles, cryptomonads, and haptophytes).
The cluster is probably polyphyletic.

Chromosomal mutation (also known as chromosomal rearrangement)

A mutation involving a long segment of DNA. These mutations can involve deletions, insertions, or inversions of sections of DNA. In some cases, deleted sections may attach to other chromosomes, disrupting both the chromosomes that loses the DNA and the one that gains it.


The physical unit of genetic material in a cell; A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated specialized proteins called histones; A single DNA molecule that is the self-replicating genetic structure within the cell which carries the linear nucleotide sequence of genes; a linear end-to-end arrangement of genes and other DNA, sometimes with associated protein and RNA.
Prokaryotes have usually one large circular chromosome carrying the entire genome, and one or more small circular extra-chromosomal DNA (plasmids). Eukaryotic genomes consist of a number of chromosomes (several to several dozen) whose DNA is associated with different kinds of proteins.
In humans (or eukaryotes), the DNA is supercoiled, compacted, and complexed with accessory proteins, and organized into a number of such structures. Normal human cells contain 46 chromosomes (except the germ cells, egg and sperm) comprising two sets of 23 chromosomes: 22 homologous pairs of autosomes and the sex-determining X and Y chromosomes (XX for females and XY for males). Each set constitutes the complete human Genome carrying approximately 35,000 genes. Each chromosome carries between 1,000 to 2,000 genes. Eukaryotic chromosomes are linear, long DNA molecules tightly packed with proteins that control their structure and activities of genes.

Chromosome aberration

Any type of change in the chromosome structure or number (deficiencies, duplications, translocations, inversions, etc.).Although it can be a mechanism for enhancing genetic diversity, such alterations are usually fatal or ill-adaptive, especially in animals.

Chromosome jumping

A technique of isolating clones from a genomic library that are not contiguous by skipping a region between known points on the chromosome. Done usually to bypass regions that are difficult or impossible to walk through or regions known not to be of interest.

Chromosome map

A diagram of the linear order of the genes on a chromosome.

Chromosome painting

The use of fluorescent-tagged chromosome-specific dispersed repeat DNA sequences to visualize specific chromosomes or chromosome segments by in situ DNA hybridization and fluorescence microscopy.

Chromosome puff

A swelling at a site along the length of a polytene chromosome; the site of active transcription. A diffuse uncoiled region in a polytene chromosome where transcription is actively taking place.

Chromosome region p

The short arm of a chromosome.

Chromosome region q

The long arm of a chromosome.

Chromosome set

The group of different chromosomes that carries the basic set of genetic information for a particular species.

Chromosome walking

A technique for cloning everything in the genome around a known piece of DNA (the starting probe). It produces sets of overlapping DNA clones for studying segments of DNA larger than can be cloned individually. It allows analysis of large regions of DNA, in which a each end of a large single cloned DNA fragment is used separately to screen recombinant DNA genome library for other clones containing neighbouring sequences.
You screen a genomic library for all clones hybridizing with the probe, and then figure out which one extends furthest into the surrounding DNA. The most distal piece of this most distal clone is then used as a probe, so that ever more distal regions can be cloned. This has been used to move as much as 200 kb away from a given starting point (an immense undertaking). Typically used to "walk" from a starting point towards some nearby gene in order to clone that gene. Also used to obtain the remainder of a gene when you have isolated a part of it.


Marked by long duration or frequent recurrence.

Chronic exposure

: A prolonged exposure occurring over days, weeks or years.

Chronic bronchitis

Increased swelling and mucus (phlegm or sputum) production in the respiratory airways. Airway obstruction occurs in chronic bronchitis because the swelling and extra mucus causes the inside of the airways to be smaller than normal. Diagnosis of chronic bronchitis is made based on symptoms of a cough that produces mucus or phlegm on most days, for three months, for two or more years (after other causes for the cough have been excluded).  (see Chronic Obstructive Pulmonary Disease)

Chronic Obstructive Pulmonary Disease (COPD)

A preventable and treatable disease that is characterized by progressive airflow limitation that cannot be fully reversed, as well as abnormal inflammation due to chronic inhalation of particles or noxious gas.  Symptoms of COPD rarely manifest in patients younger than age 40, though after onset, respiratory function declines precipitously over several years. COPD includes chronic bronchitis, emphysema, or a combination of both. (see Chronic bronchitis and Emphysema)
(Source: American Thoracic Society, Patient Information Series)


Digested content of the stomach released for further digestion in the small intestine.


A precursor of the digestive enzyme chymotrypsin (zymogen). This molecule is inactive and must be cleaved by trypsin, and then by other chymotrypsin molecules before it can reach its full activity. Its activity is the conversion of proteins to amino acids. The active site of the chymotrypsinogen is covered by a six amino acid long mask. It is only when this mask is removed - when it enters the lumen of the intestine and comes into contact with chymotrypsin molecules - that the enzyme becomes active. This is a very useful safety feature for a protein digesting enzyme. If it wasn't inactivated in this way it would digest the pancreas where it is produced.

Cilium (plural = cilia)

A short cellular appendage specialized for locomotion, formed from a core of nine outer doublet microtubules and two inner single microtubules ensheathed in an extension of plasma membrane.Hair-like extensions of the cell, consisting of cytoplasm and the smaller organelles, extending from the membrane of many eukaryotic cells. Cilia often function in locomotion. A behavioural type of eukaryotic flagellum, distinctive because they occur in large numbers, have a co-ordinated behaviour, and usually direct fluids parallel to the surface.

Ciliary body

part of the eye that joins the iris with the anterior portion of the choroid.

Circadian rhythm

A physiological cycle of about 24 hours, present in all eukaryotic organisms, that persists even in the absence of external cues.


The set of points in a plane that are a fixed distance from a given point.


The path followed by an electric current. Electricity must flow in a circuit to do useful work.

Circular functions

Same as trigonometric functions.


The point in a triangle that is the center of the circle that can be circumscribed about the triangle.   The intersection of the perpendicular bisectors of the triangle.


The distance around a closed curve. The circumference of a circle is 2*pi*r where r is the radius of the circle.


Use of other words to describe a specific word or idea which cannot be remembered

Circumscribed circle

A circle that passes through all of the vertices of a regular polygon.


Chronic liver disease characterized by gradual replacement of normal tissue by fibrous tissue leading to increasing loss of liver function. Due to several causes including alcohol abuse and viral hepatitis.

Cis and trans isomers

Isomers related by rotation about a double bond.

Cis conformation

In a heterozygote involving two mutant sites (a,b) within a gene or within a gene cluster, the arrangement ab/AB.

Cis dominance

The ability of a gene to affect genes next to it on the same chromosome. Hence cis-dominant = mutations (eg of an operator) that alter the functioning of genes on that same piece of DNA.

Cis-trans complementation test

1. A mating test to determine whether two different recessive mutations (a1;a2) on opposite chromosomes (trans, a1+/+a2) of a diploid or partial diploid will not complement (ie have a mutant phenotype) each other; but the same two recessive mutations on the same chromosome (cis, a1a2/++) in a diploid or partial diploid show a wild-type phenotype.
2. A test for allelism.
3. A test to determine whether two mutant sites are in the same functional unit or gene.


The smallest genetic unit that does not show genetic complementation when two different mutations are in trans during a cis-trans complementation test; but shows wild-type phenotype when the same mutations are in cis. Synonymous with gene.
Originally defined as a functional genetic unit within which two mutations cannot complement. Now equated with the term gene, as the region of DNA that en codes a single polypeptide (or functional RNA molecule such as tRNA or rRNA).

Citric acid cycle (Krebs citric acid cycle)

A series of chemical reactions involved in aerobic respiration that occurs naturally in animals.


A single complete branch of the Tree of Life; more formally, a monophyletic group of organisms. A monophyletic taxon; a group of organisms which includes the most recent common ancestor of all of its members and all of the descendants of that most recent common ancestor.


A taxonomic approach that classifies organisms according to the order in time at which branches arise along a phylogenetic tree, without considering the degree of morphological divergence.


The development of a new clade; the splitting of a single lineage into two distinct lineages; speciation. A pattern of evolutionary change that produces biological diversity by budding one or more new species from a parent species that continues to exist; also called branching evolution.


A diagram, resulting from a cladistic analysis, which depicts a hypothetical branching sequence of lineages leading to the taxa under consideration. The points of branching within a cladogram are called nodes. All taxa occur at the endpoints of the cladogram.


Speech in which sounds, rather than meaningful, conceptual relationships govern word choice; it may include rhyming and punning. The term is usually applied only when it is a manifestation of a pathological condition; thus, it would not be used to describe the rhyming word play of children. Example: "I'm not trying to make noise. I'm trying to make sense. If you can make sense out of nonsense, well, have fun. I'm trying to make sense out of sense. I'm not making sense (cents) anymore. I have to make dollars." Clanging is observed most commonly in schizophrenic and manic episodes.

Clasp knife reflex

Sudden release of tension of a spastic muscle that occurs near the maximum length as the muscle is gradually lengthened


A taxonomic grouping of related, similar orders; category above order and below phylum.

Classical conditioning

A type of associative learning; the association of a normally irrelevant stimulus with a fixed behavioral response.


The practice of arranging organisms in named groups (taxa).

Cleavage furrow

A constriction of the cell membrane at the equator of the cell that marks the beginning of cytokinesis (cell division) in animal cells. The cell divides as the furrow deepens.


The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane. Specifically, the succession of rapid cell divisions without growth during early embryonic development that converts the zygote into a ball of cells

Cleavage furrow

The first sign of cleavage in an animal cell; a shallow groove in the cell surface near the old metaphase plate.

Cleaved amplified polymorphic sequence (CAPS)

A technique for identifing polymorphisms at a particular locus.The locus is amplified by PCR, followed by digesting with restriction enzymes. Polymorphisms may result in different size restriction fragments.

Cleft lip / palate

A birth defect where there is a gap in the soft palate and roof of the mouth, sometimes extending through the upper lip. Results when the various parts of a lip or palate don't grow together to make a single lip or hard palate and is usually correctable. Affects eating, speech production, hearing and tooth formation. Clefting occurs during the sixth through thirteenth week of pregnancy.The degree of the cleft lip can vary greatly, from mild (notching of the lip) to severe (large opening from the lip up through the nose). Cleft lips may be caused by genetic or environmental factors.


Variation in features of individuals in a population that parallels a gradient in the environment.


Used in image processing to describe when parts of an image are removed, usually delimited by straight lines.Images which are projections of three-dimensional computer objects may be clipped in 3-D, usually by one or several delimiting plane(s).Clipping is also in use for thresholding signal amplitudes or greyvalues in an image.


A common opening for the digestive, urinary, and reproductive tracts in all vertebrates except most mammals.

Clonal selection

The mechanism that determines specificity and accounts for antigen memory in the immune system.Occurs because an antigen introduced into the body selectively activates only a tiny fraction of inactive lymphocytes, which proliferate to form a clone of effector cells specific for the stimulating antigen.


(1) A group of genetically identical cells or individuals derived by asexual division from a common ancestor:
(2) To generate identical copies of a region of a DNA molecule or to generate genetically identical copies of a cell, or organism. The identical molecule, cell, or organism that results from the cloning process.
(3) As a verb, to make one or more genetic replicas of an individual or cell; Cloning is the process of producing a genetically identical offspring or copy..
In reference to DNA: Cloning can also refer to the technical process of duplicating genetic material in the laboratory, for instance through the polymerase chain reaction (PCR). To clone a gene, one finds the region where the gene resides on the DNA and copy that section of the DNA using laboratory techniques. The it would be inserted into some type of vector (say, a plasmid) and the resultant construct put into a host (usually a bacterium) so that the plasmid and insert replicate with the host. An individual bacterium is isolated and grown and the plasmid containing the "cloned" DNA is re-isolated from the bacteria, at which point there will be many millions of copies of the DNA - essentially an unlimited supply. Actually, an investigator wishing to clone some gene or cDNA rarely has that DNA in a purified form, so practically speaking, to "clone" something involves screening a cDNA or genomic library for the desired clone.
In reference to cells grown in a tissue culture dish: a clone is a line of cells that is genetically identical to the originating cell. This cloned line is produced by cell division (mitosis) of the original cell.
In reference to organisms: Many natural clones are produced by plants and (mostly invertebrate) animals. Cloning is a natural process that underlies asexual reproduction that include the binary fission of prokaryotic cells (bacteria and archaea) and mitotic cell division of eukaryotic cells. Mitosis occurs continuously in the human body due to growth and tissue repair (wound healing) and maintenance (skin regeneration, hair growth).  The term clone may also be used to refer to an animal produced by somatic cell nuclear transfer (SCNT) or parthenogenesis.


The process of asexually producing a group of cells (clones), all genetically identical, from a single ancestor. In recombinant DNA technology, the use of DNA manipulation procedures to produce multiple copies of a single gene or segment of DNA is referred to as cloning DNA.

Cloning vector

An agent used to transfer DNA in genetic engineering, such as a plasmid that moves recombinant DNA from a test tube back into a cell, or a virus that transfers recombinant DNA by infection.DNA molecule originating from a virus, a plasmid , or the cell of a higher organism into which another DNA fragment of appropriate size can be integrated without loss of the vectors capacity for self-replication.
Vectors introduce foreign DNA into host cells, where it is replicated autonomously in large quantities. Examples are plasmids, cosmids, and yeast artificial chromosomes; vectors are often recombinant molecules containing DNA sequences from several sources.


A sustained series of rhythmic jerks following quick stretch of a muscle.The involuntary alternating contraction and relaxation of a rapidly extended muscle in spasticity.

Closed circulatory system

A type of internal transport in which blood is confined to vessels.

Closed interval

An interval that contains its endpoints.

Closed loop (reflex) movements

Reflexly controlled movements that are guided by inputs from sensory systems. See Open-loop (or volitional) movements

Cluster analysis

multivariate statistical analysis method with several variables. Used to determine if data can be separated into discrete “clusters”, each of which is characterised by a particular combination of the same group of variables or criteria so that each cluster is differentiated from another from the same broad data set.

Cluster ion

Ion formed by the combination of two or more identical ions or molecules in association with another atom, molecule, or ion.


A stinging cell containing a nematocyst; characteristic of cnidarians.


Molecules that help the transcription factors bind to the DNA in order for gene transcription to occur.

Coagulation (of blood)

The clotting of blood.
A complex process by which blood forms solid clots. It is an important part of hemostasis (the cessation of blood loss from a damaged vessel) whereby a damaged blood vessel wall is covered by a platelet- and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel. Disorders of coagulation can lead to an increased risk of bleeding and/or clotting and embolism.

Coagulation is highly conserved throughout biology; in all mammals, coagulation involves both a cellular (platelet) and a protein (coagulation factor) component. The system in humans has been the most extensively researched and therefore the best understood.

Coagulation is initiated almost instantly after an injury to the blood vessel damages the endothelium (lining of the vessel). Platelets immediately form a hemostatic plug at the site of injury; this is called primary hemostasis. Secondary hemostasis occurs simultaneously—proteins in the blood plasma, called coagulation factors, respond in a complex cascade to form fibrin strands which strengthen the platelet plug.

Platelet activation

Damage to blood vessel walls exposes collagen normally present under the endothelium. Circulating platelets bind to the collagen with the surface collagen-specific glycoprotein Ia/IIa receptor. This adhesion is strengthened further by the large multimeric circulating protein von Willebrand factor (vWF), which forms links between the platelet glycoprotein Ib/IX/V and collagen fibrils.

The platelets are then activated and release the contents of their granules into the plasma, in turn activating other platelets. The platelets undergo a change in their shape which exposes a phospholipid surface for those coagulation factors that require it. Fibrinogen links adjacent platelets by forming links via the glycoprotein IIb/IIIa. In addition, thrombin activates platelets.

The coagulation cascade.
The coagulation cascade of secondary hemostasis has two pathways, the Contact Activation pathway (formerly known as the Intrinsic Pathway) and the Tissue Factor pathway (formerly known as the Extrinsic pathway) that lead to fibrin formation. It was previously thought that the coagulation cascade consisted of two pathways of equal importance joined to a common pathway. It is now known that the primary pathway for the initiation of blood coagulation is the Tissue Factor pathway. The pathways are a series of reactions, in which a zymogen (inactive enzyme precursor) of a serine protease and its glycoprotein co-factor are activated to become active components that then catalyze the next reaction in the cascade, ultimately resulting in cross-linked fibrin. Coagulation factors are generally indicated by Roman numerals, with a lowercase a appended to indicate an active form.

The coagulation factors are generally serine proteases (enzymes). There are some exceptions. For example, FVIII and FV are glycoproteins and Factor XIII is a transglutaminase. Serine proteases act by cleaving other proteins at specific sites. The coagulation factors circulate as inactive zymogens.

The coagulation cascade is classically divided into three pathways. The tissue factor and contact activation pathways both activate the "final common pathway" of factor X, thrombin and fibrin.
Tissue factor pathway: The main role of the tissue factor pathway is to generate a "thrombin burst," a process by which thrombin, the single most important constituent of the coagulation cascade in terms of its feedback activation roles, is released instantaneously. FVIIa circulates in a higher amount than any other activated coagulation factor.
Following damage to the blood vessel, endothelium Tissue Factor (TF) is released, forming a complex with FVII and in so doing, activating it (TF-FVIIa).
TF-FVIIa activates FIX and FX.
FVII is itself activated by thrombin, FXIa, plasmin, FXII and FXa.
The activation of FXa by TF-FVIIa is almost immediately inhibited by tissue factor pathway inhibitor (TFPI).
FXa and its co-factor FVa form the prothrombinase complex which activates prothrombin to thrombin.


Thrombin then activates other components of the coagulation cascade, including FV and FVII (which activates FXI, which in turn activates FIX), and activates and releases FVIII from being bound to vWF.
FVIIIa is the co-factor of FIXa and together they form the "tenase" complex which activates FX and so the cycle continues.

Contact activation pathway: There is formation of the primary complex on collagen by high-molecular-weight kininogen (HMWK), prekallikrein, and FXII (Hageman factor). Prekallikrein is converted to kallikrein and FXII becomes FXIIa. FXIIa converts FXI into FXIa. Factor XIa activates FIX, which with its co-factor FVIIIa form the tenase complex, which activates FX to FXa. The minor role that the contact activation pathway has in initiating clot formation can be illustrated by the fact that patients with severe deficiencies of FXII, HMWK, and prekallikrein do not have a bleeding disorder.

Final common pathwayThrombin has a large array of functions. Its primary role is the conversion of fibrinogen to fibrin, the building block of a hemostatic plug. In addition, it activates Factors VIII and V and their inhibitor protein C (in the presence of thrombomodulin), and it activates Factor XIII, which forms covalent bonds that crosslink the fibrin polymers that form from activated monomers.

Following activation by the contact factor or tissue factor pathways the coagulation cascade is maintained in a prothrombotic state by the continued activation of FVIII and FIX to form the tenase complex, until it is down-regulated by the anticoagulant pathways.

Cofactors: Various substances are required for the proper functioning of the coagulation cascade:
Calcium and phospholipid (a constituent of platelet membranes) are required for the tenase and prothrombinase complexes to function. Calcium mediates the binding of the complexes via the terminal gamma-carboxy residues on FXa and FIXa to the phospholipid surfaces expressed by platelets as well as procoagulant microparticles or microvesicles shedded from them. Calcium is also required at other points in the coagulation cascade.
Vitamin K is an essential factor to a hepatic gamma-glutamyl carboxylase that adds a carboxyl group to glutamic acid residues on factors II, VII, IX and X, as well as Protein S, Protein C and Protein Z. Deficiency of vitamin K (e.g. in malabsorption), use of inhibiting anticoagulants (warfarin, acenocoumarol and phenprocoumon) or disease (cirrhosis, hepatocellular carcinoma) impairs the function of the enzyme and leads to the formation of PIVKAs (proteins formed in vitamin K absence) this causes partial or non gamma carboxylation and affects the coagulation factors ability to bind to expressed phospholipid.

Inhiibtors: Three mechanisms keep the coagulation cascade in check. Abnormalities can lead to an increased tendency toward thrombosis:
Protein C is an important co-factor inhibitor, which degrades the co-factors FVa and FVIIIa. It is activated by thrombin with thrombomodulin and requires its co-enzyme Protein S to function. Quantitative or qualitative deficiency of either may lead to thrombophilia (a tendency to develop thrombosis). Impaired action of Protein C (activated Protein C resistance), for example by having the "Leiden" variant of Factor V or high levels of FVIII also may lead to a thrombotic tendency.
Antithrombin is a serine protease inhibitor (serpin) that degrades the serine proteases; thrombin and FXa, as well as FXIIa, and FIXa. It is constantly active, but its adhesion to these factors is increased by the presence of heparan sulfate (a glycosaminoglycan) or the administration of heparins (different heparinoids increase affinity to F Xa, thrombin, or both). Quantitative or qualitative deficiency of antithrombin (inborn or acquired, e.g. in proteinuria) leads to thrombophilia.
Tissue factor pathway inhibitor (TFPI) inhibits F VIIa-related activation of F IX and F X after its original initiation.

Fibrinolysis: Eventually, all blood clots are reorganised and resorbed by a process termed fibrinolysis. The main enzyme responsible for this process (plasmin) is regulated by various activators and inhibitors.

Coanda effect

It describes the tendency of moving air of fluids to follow the nearby curved or inclined surface. Described by Henri Coanda, a Romanian scientist, in the 1930's.


Rounded in shape, ball-like.


The complex, coiled organ of hearing that is responsible for starting the process of signalling via nerve fibres to the brain information about sound. The cochlea, also known as inner ear, contains the organ of Corti where hair cells convert mechanical motion, induced by sound waves striking the ear drum, into Action Potentials in nerve cells. These nerve cells then transmit that information to the brain where it is decoded and interpreted.

Code (in data entry)

In most numeric data files, answers to questions are recorded with numbers rather than text and often even numeric answers are recorded with numbers other than the actual response. The numbers used in the data file are called "codes." Thus, for instance, when a respondent identifies herself as a member of a particular religion, a "code" of 1 might be used for Catholic, a 2 for Jewish, etc. Likewise, a person's age of 18 might be coded as a 2 indicating "18 or over." The codes that are used and their correspondence to the actual responses are listed in a codebook . The genetic code is the information needed to translate a nucleic acid (gene) sequence into an amino acid (protein) sequence. The code consists of triplet structures called codons such as UUG meaning two uracil and one guanine base along the messenger RNA template. This codon is recognized through base pairing by an anti-codon (triplet) on a transfer RNA. The transfer RNA is a specialized small ribonucleic acid that identifies genetic sequences on messenger RNAs (with the help of ribosomes) and carries one specific amino acid. An amino acid always matches one particular anti-codon. There are twenty amino acids to choose from for protein synthesis, and a total of 64 triplet codons (four bases in triplet sequence = 4x4x4 combinations). Thus there are 64 codons to match 20 amino acids, which means that some amino acids are coded by more than one codon. Which codons are responsible for which amino acid is evolutionarily conserved and most organisms have the same code or translation table. There are some alternate assignments found in mitochondrial genomes, viral genomes and some bacterial genomes. Yet, the fact that most organisms, bacteria, archaea and eukarya use the same genetic code explains the ability for recombinant DNA technology, i.e., to cut and past genetic elements from one organism into an other organism, since the assign amino acids to the same codons. Thus a human gene can be expressed in bacteria or yeast or jelly fish, and jelly fish genes can be expressed in bacteria, plants, fungi, animals and protists. There are almost limitless combinations possible. Read more about genetic codes at the National Center for Biotechnology Information and see the standard genetic code for humans and most organisms.


Generically, any information on the structure, contents, and layout of a data file.
Typically, a codebook includes: column locations and widths for each variable ; definitions of different record types ; response codes for each variable; codes use to indicate non-response and missing data; exact questions and skip patterns used in a survey; and other indications of the content of each variable. Many codebooks also include frequencies of response. Codebooks vary widely in quality and amount of information included. They may be machine-readable or paper copy or microfiche.

Code dictionary

A listing of the 64 possible codons and their translational meanings (the corresponding amino acids).


A phenotypic situation in which both alleles are expressed in the heterozygote.

Coding efficiency

A measure of what fraction of the information contained in the neural spike train (i.e., a train of action potentials in a neuron) is actually used to code a stimulus
Coding Efficiency = Information Rate / Entropy rate in spike train

Coding sequences

Sequences of nucleotides that signal RNA and proteins.
(see also Non-coding sequences). Introns are not coding sequences; nor are the 5' or 3' untranslated regions (or the flanking regions, for that matter - they are not even transcribed into mRNA). The coding sequence in a cDNA or mature mRNA includes everything from the AUG (or ATG) initiation codon through to the stop codon, inclusive. Hence Coding strand (or Sense strand) = The DNA strand with the same sequence as the transcribed mRNA (given U in RNA and T in DNA) and containing the linear array of codons which interact with anticodons of tRNA during translation to give the primary sequence of a protein.


A section of DNA (three nucleotide pairs in length) or RNA (three nucleotides in length) that codes for a single amino acid or termination signal.
Coding sequence (of DNA, the genetic code) made up of different combinations of 3 nucleotides in mRNA that code for a corresponding amino acid during protein synthesis.A sequence of nucleotides in a gene that signifies a start (start codon) or end (stop or termination codon) segment for a strip of DNA that is to be read out during transcription. In an mRNA, a codon is a sequence of three nucleotides which codes for the incorporation of a specific amino acid into the growing protein. The sequence of codons in the mRNA unambiguously defines the primary structure of the final protein. Of course, the codons in the mRNA were also present in the genomic DNA, but the sequence may be interrupted by introns.

Codon repeat

A three letter sequence of bases (codon) that is repeated consecutively in a section of DNA.


A constant that multiplies a variable. In Ax + By = C, A and B are coefficients of x and y.

Coefficient of determination

The coefficient of determination, r 2,is useful because it gives the proportion of the variance (fluctuation) of one variable that is predictable from the other variable.
(see Correlation coefficient)
It is a measure that allows us to determine how certain one can be in making predictions from a certain model/graph.
The coefficient of determination is the ratio of the explained variation to the total variation.
The coefficient of determination is such that 0 < r< 1,  and denotes the strength of the linear association between x and y
The coefficient of determination represents the percent of the data that is closest to the line of best fit.
For example, if r = 0.922, then 2 = 0.850, which means that 85% of the total variation in y can be explained by the linear relationship between and y (as described by the regression equation).  The other 15% of the total variation in y remains unexplained.
The coefficient of determination is a measure of how well the regression line represents the data.  If the regression line passes exactly through every point on the scatter plot, it would be able to explain all of the variation. The further the line is away from the points, the less it is able to explain.

Coefficient of Variation (CV)

A statistical measurement of the distribution of responses around the mean of those values; A statistical representation of the precision of a test.
Defined as = 100% x Standard Deviation /  Mean. The percent coefficient of variation is the standard deviation of the peak divided by the mean channel number of the peak, times 100. Percent coefficient of variation (%CV ) is a measure of peak distribution.
The CV is only applicable for values which come from a gaussian distributed population. It is derived by dividing the standard deviation of the replicate adjusted or normalized response measurements by the mean of the replicate measurements (times 100 for percent). Since the measurement units are canceled out, the %CV is a relative value that is independent of the magnitude of the replicate response measurements.

Coeliac disease (Also referred to as celiac sprue and gluten-induced enteropathy)

A chronic disease of the intestines that damages the body's ability to
absorb, or retain nutrients as food moves through the intestines.It results in diarrhea or constipation, loss of appetite, growth problems and wasting of muscle. Believed to be a genetically transferred deficiency. Age of onset, 4 months to 16 years. Sensitivity to the gluten portion of wheat, oats, barley, and rye flour or cereals is responsible for the symptoms of the disease.


A body cavity completely lined with mesoderm. A fluid-filled body cavity in animals, lined with tissue of mesodermal origin, housing the internal organs.


An animal whose body cavity is completely lined by mesoderm, the layers of which connect dorsally and ventrally to form mesenteries.


Referring to a multinucleated condition resulting from the repeated division of nuclei without cytoplasmic division. Condition in which an organism consists of filamentous cells with large central vacuoles, and whose nuclei are not partitioned into separate compartments. The result is a long tube containing many nuclei, with all the cytoplasm at the periphery


Small non-protein organic molecules that help enzymes carry out biochemical reactions. Essential coenzymes are also known as vitamins. They bind to an enzyme and are required for its catalytic activity. Many of the vitamins are coenzymes or are converted into coenzymes in the body.


The mutual influence on the evolution of two different species interacting with each other and reciprocally influencing each other's adaptations.


Any nonprotein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely with the substrate during catalysis.


The cofunction of a trigonometric function, f(x), is equal to f(pi/2 - x).  The cofunction of the sine is the cosine.   The cofunction of the secant is the cosecant.  The cofunction of the tangent is the cotangent.


The process or processes by which an organism gains knowledge or becomes aware of events or objects in its environment and uses that knowledge for comprehension and problem-solving; The conscious process of knowing or being aware of thoughts or perceptions, including understanding and reasoning. The high level functions carried out by the human brain, including comprehension and use of speech, visual perception and construction, calculation ability, attention (information processing), memory, and executive functions such as planning, problem-solving, and self-monitoring.

Cognitive Rehabilitation

Therapy programs which aid persons in the management of specific problems in perception, memory, thinking and problem solving. Skills are practiced and strategies are taught to help improve function and/or compensate for remaining deficits. The interventions are based on an assessment and understanding of the person's brain-behavior deficits and services are provided by qualified practitioners.

Cogwheel rigidity.

The form of rigidity of Parkinsonism in which the muscle lengthens in a series of little jerks when it is stretched.

Coherent spectroscopy

The use of lasers to study the coherent interactions of excited atoms or molecules.


The binding together of like molecules, often by hydrogen bonds

Cohesion species concept

The idea that specific evolutionary adaptations and discrete complexes of genes define species.

Cohesion-tension theory

A theory accounting for the upward movement of water in plants. According to this theory, transpiration of a water molecule results in a negative (below 1 atmosphere) pressure in the leaf cells, inducing the entrance from the vascular tissue of another water molecule, which, because of the cohesive property of water, pulls with it a chain of water molecules extending up from the cells of the root tip.

Cohesive end

A single-stranded end to a linear duplex DNA molecule which can hydrogen-bond with a complementary single-strand base sequence from the end of the same or another DNA molecule.


A purification procedure to determine if two different molecules (usually proteins) interact. An antibody specific to the protein of interest is added to a cell lysis. Then the antibody-protein complex is pelleted usually using protein-G sepharose which binds most antibodies. If there are any protein/molecules that bind to the first protein, they will also be pelleted. Identification of proteins in the pellet can be determined by western blot (if an antibody exist) or by sequencing a purified protein band.


A fusion of two elements. An intermediate structure in replicative transposition. The product of the fusion of two circular elements to form a single, larger circle.

Coisogenic or congenic

Nearly identical strains of an organism that vary at only a single locus.

Cold aclimation response

The process by which plants increase their tolerance to freezing by exposure to low, nonfreezing temperatures.


Any fermentative (specifically lactose-fermenting) Gram-negative anaerobic enteric bacilli (E. coli-like). These bacteria (primarily E. coli and Enterobacter aerogenes) are used as an indicator of the sanitary quality of food. High levels of coliforms indicate the presence of fecal contamination in food and water.


Inflammation of the large intestine (the colon). There are many forms of colitis , including ulcerative colitis , Crohn's disease , infectious, pseudomembranous, and spastic. For example, intermittent rectal bleeding , crampy abdominal pain and diarrhea can be symptoms of ulcerative colitis. Diagnosis can be made by barium enema, but direct visualization (sigmoidoscopy or colonoscopy ) is the most accurate test. Long-standing ulcerative colitis increases the risk for colon cancer . Ulcerative colitis can also be associated with inflammation in joints, spine, skin, eyes, the liver and its bile ducts. Treatment of ulcerative colitis can involve medications and surgery.


A glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom.

Collecting duct

The location in the kidney where filtrate from renal tubules is collected; the filtrate is now called urine.

Colligative properties

Properties which depend on the number of molecules in solution, a function of concentration and molecular weight, rather than just on the total percent concentration.  Such properties include boiling point elevation, freezing point depression, and osmotic concentration.


Points which lie on the same line.

Col plasmid

Plasmid that produces an antibiotic (colicin) used by the host to kill other strains of bacteria.


A 1:1 linear correspondence between two related series of items.
e.g., The one to one linear correspondence between the order of codons in a coding sequence and the order of amino acids in the protein encoded.


Condition in which many unicellular organisms live together in a somewhat coordinated group. Unlike true multicellular organisms, the individual cells retain their separate identities, and usually, their own membranes and cell walls.

Colony-forming unit

A unit of measurement for fungal or bacteria samples


Visualization of the lining of the anus, rectum and colon through a rigid proctosigmoidoscope or a flexible fiber optic endoscope. Allows diagnosis of tumors and inflammatory diseases.

Colorectal cancer

A malignant disease of the colon and/or rectum which often begins as a polyp.
The first indication of colorectal cancer is usually hidden, or occult, blood in the stool. Symptoms may include changes in bowel habits (diarrhea, constipation) or in consistency or color of the stool. A stool specimen blood test is commonly performed to screen for colorectal cancer.

Colorimetric label

A colorimetric label is an enzyme system in which an enzyme linked to a ligand or binder reacts with a specific substrate to generate a chromophore product. This tracer conjugate is quantified by measuring the amount of light absorbed by the product at a specific wavelength. Enzymes commonly used to label ligands or binders include alkaline phosphatase using para-nitrophenyl phosphate as substrate, horseradish peroxidase using hydrogen peroxide/coupler as substrate, and b-galactosidase using o-nitrophenylgalactoside as substrate.

Column (in data entry)

In a data file, a single vertical column each being one byte in length. Fixed format data files are traditionally described as being arranged in lines and columns. In a fixed format file, column locations describe the locations of variables.

Column location (in data entry)

The precise location in a data file of a variable expressed in column numbers, beginning with the first column in a physical record as column number 1


A state of unconsciousness from which the patient cannot be awakened or aroused, even by powerful stimulation; lack of any response to one's environment. Defined clinically as an inability to follow a one-step command consistently; Glasgow Coma Scale score of 8 or less.

Combustible liquid

Liquids having a flash point at or above 100 degrees. Not as ignitable as Flammables.

Commercial water use

Water used for motels, hotels, restaurants, office buildings, other commercial facilities, and institutions. Water for commercial uses comes both from public-supplied sources, such as a county water department, and self-supplied sources, such as local wells.

Comma Separated Variable (CSV)

The simplest form of file for holding scientific, or other, data. Data is listed in columns in a text file, each value being separated by a comma. Each new line represents a new set of data. This format is used mainly on Windows-based PCs while Apple Macintosh computers tend to use the TSV format. (see also Tab Separated Variable)


An organism that derives nourishment or shelter by living in close association with another organism (the host), without damaging the host;  Organisms existing in or on an animal or human without causing disease. Commensalism = A symbiotic relationship in which the symbiont benefits but the host is neither helped nor harmed

Communicative Disorder

An impairment in the ability to 1) receive and/or process a symbol system, 2) represent concepts or symbol systems, and/or 3) transmit and use symbol systems.
The impairment may be observed in disorders of hearing, language, and/or speech processes.

Commutative property

a + b = b + a.   a*b = b*a.

Compact bone  

The outer dense layer that forms the shaft of the long bones; made up of concentric layers of mineral deposits surrounding a central opening.

Comparison Probability

The comparison probability (Cpr Prob) is the probability that a standard curve is not significantly different from the reference assay standard curves.
In the case of a logistic curve fit, the comparison probability should be evaluated in conjunction with the parallel probability. Linear regressions are straight lines and a comparison probability is not computed.

Comparative genomic hybridization (CGH)

CGH and FISH is a method for analyzing genomic DNA for unbalanced genetic alterations. Genomic DNA from the test sample (e.g., tumor cells) is labeled (e.g., orange/red) and mixed with normal genomic DNA labeled another color (e.g., green) and the mixture is hybridized (FISH) to a normal human metaphase spread or other reference standard. Regions of imbalance (increased or decreased copy number) in the tumor are located or mapped relative to the normal metaphase chromosomes as increases or decreases in the green to orange/red fluorescence ratio

Compensation (in electronics)

An electronic calculation that removes signal overlap which the optical system cannot remove.e.g., Fluorescence compensation works for specific pairs of fluorescent parameters.


Interaction between members of the same population or of two or more populations using the same resource, often present in limited supply.

Competitive antagonist

See antagonist.

Competitive  assay

In this type of assay, a single concentration of radioligand is used in every assay tube (unlike the saturation experiment, in which the radioligand concentration is varied). The ligand is used at a low concentration, usually at or below its KD value. The level of specific binding of the radioligand is then determined in the presence of a range of concentrations of other competing non-radioactive compounds, in order to measure the potency with which they compete for the binding of the radioligand. Competition curves may also be computer-fitted to a logistic function as described under direct fit.

Competitive binding assay

A competitive binding assay is an immunoassay reaction which is based upon the competition of labeled and unlabeled ligand for a limited number of binding sites on the binder. A fixed amount of labeled ligand (tracer) and a variable amount of unlabeled ligand are incubated with the binder. Following the law of mass action, the amount of labeled ligand which can bind to the binder is a function of the total concentration of labeled and unlabeled ligand. As the concentration of unlabeled ligand is increased, less labeled ligand can bind to the binder and the measured response is decreased. The standard curve of a competitive binding assay has a negative slope and is generally symmetrical at the midpoint

Competitive exclusion principle

The concept that when the populations of two species compete for the same limited resources, one population will use the resources more efficiently and have a reproductive advantage that will eventually lead to the elimination of the other population.

Competitive inhibitor

A substance that reduces the activity of an enzyme by entering the active site in place of the substrate whose structure it mimics.

Complementary angles

Two angles are complementary if their sum is 90 degrees.

Complementary DNA

See cDNA
A DNA molecule made in vitro using mRNA as a template and the enzyme reverse transcriptase. A cDNA molecule therefore corresponds to a gene, but lacks the introns present in the DNA of the genome.

Complementary nucleotides (Also known as Complementary base pairing)

The bonding preferences of nucleotides.
Of the nucleotides Adenine binds with Thymine, and Cytosine with Guanine.

Complement cascade

The precisely regulated, sequential interaction of proteins (in the blood) that is triggered by a complex of antibody and antigen to cause lysis of infected cells.
The triggering of lysis by multivalent antibody- antigen complexes is mediated by the classical pathway, beginning with the activation of C1, the first component (protein) of the pathway. This activation step, in which C1 undergoes conversion from a zymogen to an active protease, results in sequential cleavage of the C4, C2, C3, and C5 components (proteins). C5b, a fragment of C5, then joins C6, C7, and C8 to penetrate the (cell) membrane bearing the antigen. Finally, the binding of some 16 molecules of C9 to this "bridgehead" produces large pores in the (cell) membrane, which cause the lysis and destruction of the target cell.

Complement fixation  

An immune response in which antigen-antibody complexes activate complement proteins.

Complement system  

A chemical defense system that kills microorganisms directly; a component of he body’s innate immune system. A group of at least 20 soluble proteins found in blood serum that interacts in a sequential fashion, in which a precursor molecule is converted into an active enzyme. Each enzyme uses the next molecule in the system as a substrate and converts it into its active (enzyme) form. This cascade of events and reactions leads ultimately to the formation of an attack complex that forms a transmembrane channel in the cell membrane (e.g., of a pathogen). It is the presence of the channel that leads to lysis (rupturing) of the cell. It supplements the inflammatory response, and works with, or complements, the immune system.
It can amplify the inflammatory response, enhance phagocytosis, or directly lyse pathogens. It is activated by the onset of the immune response or by surface antigens on microorganisms or other foreign cells.

Complete digestive tract

A digestive tube that runs between a mouth and an anus; also called alimentary canal.
An incomplete digestive tract has only one opening.

Completing the square

The method of adding an expression to both sides of an equation so that one side becomes a perfect square trinomial.

Complex fraction

A fraction that contains a fraction in its numerator and/or denominator.


Complexity is the measure of the number and strength of interactions of its components. The components are organized not in a linear chain, but a network with specific connectivity, branches and loops. Network components affect each other through their interactions (molecular interactions). Complexity in biology is the result of dynamic interactions that follow each other in time and with both forward and feedback loops. Because of loops, the output of a network will affect a future input, thus continuously adjusting the physical output value of the system. Biological networks have evolved as stable systems. Stability means that biological systems are in homeostatic equilibrium, with information constantly flowing through the system and the output kept within a narrow range.

Complex number

The sum of an imaginary number and a real number written in the form a + bi or r(cos x + isin x).


The components in the vector (a, b, c) are a, b, and c.

Composite function

A function that consists of two functions arranged in such a way that the output of one function becomes the input of the other function.

Composite hypothesis

A hypothesis with one or more free parameters. As an example, the hypothesis that the decay of a given particle is purely exponential with unknown lifetime, is a composite hypothesis. The testing of a composite hypothesis involves first estimating the unknown parameter(s). In the actual test, it is then necessary to compensate for the fact that the parameter(s) has (have) been fitted using the same data. Since one typically knows how to do this correctly only in the asymptotic limit of a large amount of data, such tests are never as safe as tests of simple (completely defined) hypotheses.

Composite number

A natural number that is not prime.


A chemical combination, in a fixed ratio, of two or more elements. From the Latin word componere = to put together.

Compound eye

A type of multifaceted eye in insects and crustaceans consisting of up to several thousand light-detecting, focusing ommatidia; especially good at detecting movement


Understanding of spoken, written, or gestural communication.

Compulsion (as in disoreder)

An insistent, repetitive, intrusive and unwanted urge to perform an act
that is contrary to the person's ordinary wishes or standards. Since it serves as a defensive substitute for still more unacceptable unconscious ideas and wishes, failure to perform the compulsive act leads to overt anxiety. Compulsions are obsessions that are still felt as impulses.

Compulsive personality disorder

Restricted ability to express warm and tender emotions; preoccupation with rules, order, organization, efficiency and detail; excessive devotion to work and productivity to the exclusion of pleasure, indecisiveness.


A figure is concave if a line segment can be drawn so that it goes in, out, then back into the figure.


1. The concentration of a substance is a measurement of the mass of the substance per unit volume.
2. Maintaining attention on a task over a period of time; remaining attentive and not easily diverted.
The mass may be expressed in grams, moles, international units (IU), or other units. The liquid volumn may be expressed in milliliters or other units of volumn. Sometimes only the total mass of the analyte is used. One standard test results are often the ratio of sample to index standard response alone. The index standard can have a predetermined concentration which is then multiplied times the ratio for a concentration in whatever units are entered.

Concentration gradient

A regular increase or decrease in the intensity or density of a chemical substance.
Cells often maintain concentration gradients of H+ ions across their membranes. When a gradient exists, the ions or other chemical substances involved tend to move from where they are more concentrated to where they are less concentrated.

Concentration scale

The analyte concentration scale is the scale used to graph the analyte concentration on the x-axis. The analyte concentration can be graphed on a logarithmic scale or on a linear scale.

Concentration ratio

Concentration of agonist producing a defined response (usually but not necessarily 50% of maximum) in the presence of an antagonist, divided by the concentration producing the same response in the absence of antagonist. In figure B above the concentration ratio for curve B relative to control curve A is equal to the EC50 for curve B divided by the EC50 for curve A, i.e. 3x10(-8) / 1x10(-8) = 3.

Concentration units

The concentration units are the units of measurements used to quantify the analyte

Conclusion (in mathematics)

The part of an if - then statement that follows the word "then".   Consequent.

Concrete learning

A person's learning or cognitive style characterized as learning most efficiently by use of objects and tangible items.

Concrete thinking

A style of thinking in which the individual sees each situation as unique and is unable to generalize from the similarities between situations. Language and perceptions are interpreted literally so that a proverb such as "a stitch in time saves nine" cannot be readily grasped.


The common result of a blow to the head or sudden deceleration usually causing an altered mental state, either temporary or prolonged. Physiologic and/or anatomic disruption of connections between some nerve cells in the brain may occur. Often used by the public to refer to a brief loss of consciousness.


When a substance changes state from a gas to a liquid. The process of water vapor in the air turning into liquid water. Water drops on the outside of a cold glass of water are condensed water. Condensation is the opposite process of evaporation.

Condensation reaction

A reaction in which two molecules become covalently bonded to each other through the loss of a small molecule, usually water. Also called dehydration reaction.

Conditional statement

An if - then statement.

Conditioned play audiometry

Evaluation method for hearing sensitivity used by an audiologist where the child participates in a play activity (putting a ring on a cone, a block in a box, etc.) each time the signal is heard.

Conditioned response

The response to a stimulus that occurs when an animal has learned to associate the stimulus with a certain positive or negative effect.


The flow of current (charged molecules and elements and measured in 'Siemens'); the inverse of resistance as defined by Ohm's law V = IR, where V is the voltage, R the resistance, and I the current.
In biological systems conductance refers to the flow of ions such as sodium, potassium, and chloride and is the proportionality factor relating current to a voltage difference.
Membrane conductance depends on (a) the permeability of the membrane to ions and (b) the availability of the specific ions to flow through the respective permeability channels.


- a thing that transmits heat, electricity, light, sound or other form of energy.

Conduct disorder

A condition characterized by repetitive and persistent patterns of behavior that violate either the rights of others or age appropriate social norms or rules.
Such behaviors may include overt physical aggressions, disruptiveness, negativism, irresponsibility, and defiance of authority.


Heat or electricity transfer through molecular interaction, eg: heat passing along a metal bar.

Conductive hearing loss

A type of hearing impairment that occurs when sound is not transmitted efficiently through the ear canal, ear drum, or the bones of the middle
ear, reducing the loudness or clarity of sound that is heard. Frequent colds, allergies, or certain childhood illnesses may cause a blockage of sound due to fluid in the middle ear, and lead to temporary hearing loss or even permanent damage. Build up of ear wax; inflammation or infection in the middle ear canal; heredity; and birth defects may also cause conductive hearing loss. This kind of hearing loss can often be medically or surgically corrected.

Conductivity (electrical)

Physical property of a material that determines its ability to conduct electricity.
Expressed in Siemens per cm (S/cm).  In ohmic heating, it enables heating to occur.

Conductivity (thermal)

Physical property of a material which determines its ability to conduct heat. Expressed in Watts/meter oC


The union of all line segments that connect a point and a closed curve in a different plane from the point.


photoreceptor cells in the retina used under conditions of bright illumination;are color coded (red, green, and blue); mediate fine detail vision; contain photopigments with low sensitivity to light (i.e., cannot see colors in dim illumination).


Fabrication of facts or events in response to questions about situations or events that are not recalled because of memory impairment.  Verbalizations about people, places, and events with no basis in reality. May be a detailed account delivered. Differs from lying in that the person is not consciously attempting to deceive. Confabulation is common in organic amnestic syndrome.

Confidence limit

A statistical measure of the reliability of biological data values. Usually, 95% confidence limits are quoted. These would enclose the true value in 95% of repeated experiments.

Confidence level

A measure usually associated with the comparison of observed value(s) with a probability density function (pdf). It expresses the probability that the observation is as far as observed or further away from the most probable value of the pdf, i.e., it corresponds to the integral over the pdf from the observed value to infinity.
confidence interval, bounded by confidence limits, is an estimate for the range of values which an unkown parameter could take, given a confidence level. Confidence levels are often expressed as a percentage, e.g. it is 95% likely that a value of 11.07 or larger does not belong to a c2 distribution with five degrees of freedom.

Confidence range

A numerical interval for a single parameter. This numerical interval is the range which encompasses a specified percentage of the corresponding parameter from the reference assay runs.


A state in which a person is bewildered, perplexed, or unable to self-orient.


Present at birth. A condition or disease existing at birth, that is not necessarily caused by inheritance.

Congenital aphasia

The inability from birth to comprehend or produce language. This cannot be explained by sensory or motor defects or diffuse cerebral dysfunction.

Congenital adrenal hyperplasia

Refers to a group of inherited adrenal gland disorders. People with this condition do not produce enough of the hormones cortisol and aldosterone, and produce too much of androgen.Newborn girls with this disorder have a swelling of the clitoris (ambiguous genitalia). Newborn males may have no obvious changes but may enter into puberty as early as age 2-3 years.   Salt wasting is a lack of aldosterone causing a child to lose large amounts of salt in his/her urine.  Non salt wasting is a lack of cortisol with enough aldosterone.

Congenital blindness/adventitious deafness

An individual who has been visually impaired or blind since birth or early childhood and experiences hearing loss in adult life. Most common cause is trauma or infection.

Congenital deafness/adventitious blindness

An individual who has been hearing impaired or deaf from birth or early childhood and  experiences vision loss in adult life.
Most common cause is Usher's Syndrome, the combination of congenital deafness and Retinitis Pigmentosa.

Congenital heart disease (also termed Congenital Heart Defects)

Deformities, diseases, etc., in the heart and closely-allied blood vessels which are either present at birth, or which, being transmitted direct from the parents, show themselves some time after birth. Heart defects are the most common birth defect in the United States, occurring in about 1% of all live births, or a total of 40,000 newborns a year. CHDs include atrial and ventricular septal defects, patent ductus arteriosus, pulmonary stenosis and other valvular diseases, coarctation of the aorta, double outlet right ventricle, transposition of the great arteries, and hypoplastic left heart syndrome.

Congenital Hypothyroidism

A disease in which the thyroid glands fail to develop normally. As a result, there is little or no thyroid hormone, which is necessary for normal growth and development of children.

Congenital rubella

German measles contracted by a mother during pregnancy, which causes a variety of problems, including mental retardation, deafness, blindness, and other neurological problems.

Congenital syphilis

Syphilis transmitted from a pregnant mother to her unborn child, which may cause spontaneous abortion, stillbirth, or other problems in the child.

Congestive heart failure

Heart failure or improper functioning because of an unnatural accumulation of fluids around the organ.


Shapes or angles are congruent if you could put one on top of the other, and they would look like just one shape.   Equal.

Conic section

Parabola, hyperbola, ellipse, circle.   Formed by the intersection of a plane with a right circular cone.


A statement that seems to be true, but has not yet been proven.

Conjoint analysis

Analytical methods which measure the contribution of single productc omponents to an overall result.  Example, in olfactory perception, the contribution of single product components to the perception or preference formation on the basis of integral consumer judgments.


The conjugate of a complex number is formed by reversing the sign on the  imaginary part of the number.   The conjugate of a + bi is a - bi.

Conjugate eye movements

Both eyes move simultaneously in the same direction; Rotation of the eyes in the same direction at the same time. Convergence of the eyes toward the midline (crossed eyes) is a disconjugate movement.


In bacteria, the transfer of DNA between two cells that are temporarily joined. A type of sexual event during which two cells fuse. It may or may not lead to reproduction.


A statement that is really two statements joined by the word AND.   Both parts must be true for the statement to be considered true.


thin layer of mucous membrane lining the inner surface of each eyelid,
moves over the eyeball as a protective cover.

Connective tissue

Animal tissue composed of cells embedded in a matrix (gel, elastic fibers, liquid, or inorganic minerals). Functions mainly to bind and support other tissues, having a sparse population of cells scattered through an extracellular matrix.  Includes loose, dense, and fibrous connective tissues that provide strength (bone, cartilage), storage (bone, adipose), and flexibility (tendons, ligaments).

Consensus profiling

Quantitative and qualitative description of all product-relevant attributes, with the final evaluation taking place in a group discussion.

Consensus sequence

A ‘nominal’ sequence inferred from multiple, imperfect examples. Multiple lanes of shotgun sequence can be merged to show a consensus sequence. The optimal sequence of nucleotides recognized by some factor. A DNA binding site for a protein may vary substantially, but one can infer the consensus sequence for the binding site by comparing numerous examples. For example, the (fictitious) transcription factor ZQ1 usually binds to the sequences AAAGTT, AAGGTT or AAGATT. The consensus sequence for that factor is said to be AARRTT (where R is any purine, i.e. A or G). ZQ1 may also be able to weakly bind to ACAGTT (which differs by one base from the consensus).

Consensual light reflex

Constriction of the pupil of the eye opposite that into which a light is shown

Consequent (in mathematics)

The part of an "if - then" statement that follows the "then".   Conclusion.

Conservative replication (of DNA)

A proposed model of DNA replication. In this model the DNA helix is not unwound but somehow produces an entirely new strand of DNA. (see SemiConservative replication and Dispersive replication)

Conserved sequence

base sequence in a DNA molecule (or an amino acid sequence in a protein) that has remained essentially unchanged throughout evolution.

Consistency check

A process of data cleaning which looks for inappropriate responses to branched questions. For instance, one question might ask if the respondent attended church last week; a response of "no" should skip the questions about church attendance and code the answers to those questions as "inapplicable." If those questions were coded any other way than "inapplicable this would be inconsistent with the skip patterns of the survey instrument.


A member of the same species.


A value that does not change.

Constitutional delay of growth (late bloomer)

A normal variation of growth. A child will grow at a normal rate but appears smaller than children the same age. The bone age and the start of puberty are usually delayed.
The child with constitutional delay of growth tends to have a catch up growth spurt at puberty reaching a normal adult height.


In statistics means the same as degrees of freedom, i.e. the number of degrees of freedom is equal to the number of independent constraints. Note that constraint equations are not independent if they contain free parameters, as eliminating one unknown costs one equation.

Construct validity

The degree to which inferences can legitimately be made from the operationalizations (the translation of a concept or construct into a functioning and operating reality) in a study to the theoretical constructs on which those operationalizations were based. Construct validity involves generalizing from your program or measures to the concept of your program or measures. Cn be considered a "labeling" issue, e.g., when you implement a program that you call a "Head Start" program, is your label an accurate one? When you measure what you term "self esteem" is that what you were really measuring?

Consensus site

A sequence of similar (or very similar) nucleotide bases which is recognised by a transcription factor or RNA polymerase

Consumptive use

That part of water withdrawn that is evaporated, transpired by plants, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water environment. Also referred to as water consumed.

Containing group

A given group's containing group is that group in which this group is included as a subgroup. Any group in the Tree of Life has a series of hierarchically nested containing groups going all the way down to the ultimate containing group, Life on Earth.

Content errors

Common errors made by children with language problems in which the semantics, or what the child understands or talks about, is limited or inaccurate.
E.g., The "match" can have multiple meanings.

Contextual influences:

Influences arising as a result of the experimental conditions. Example, the way in which fatigue or alcohol or drug comsumption affects a person’s performance at a task; the way in which other stimuli in the background or what else the animal is doing influences the way in which a brain cell responds to a particular standard stimulus.


A set of overlapping sequence fragments which constitute a chromosomal region. (The term comes from a shortening of the word ‘contiguous’.)
Ultimately sufficient contigs add up to an entire chromosome.
More often, the term ‘contig’ is used to refer to the final product of a shotgun sequencing project. When individual lanes of sequence information are merged to infer the sequence of the larger DNA piece, the product consensus sequence is called a ‘contig’.Hence Contigs = Groups of clones representing overlapping regions of a genome and Contig map = A map depicting the relative order of a linked library of small overlapping clones representing a complete chromosomal segment. (Also called the ‘minimal tiling path’.)

Continuous (in mathematics)

A function is continuous if you can draw it without lifting your pencil off the paper.  
y = f(x) is continuous at a if
1.  f(a) exists.  
2.  lim as x-->a f(x) exists.
3.  lim as x-->of f(x) = f(a).

Continuous Positive Airway Pressure (CPAP)

The application of continuous pressure (both inspiration and expiration) for the spontaneously breathing patient.

Continuous variation

A gradation of small differences in a particular trait, such as height, within a population; occurs in traits that are controlled by a number of genes.


The prevention of pregnancy.

Contractile vacuole

In many protists, a specialized vacuole with associated channels designed to collect excess water in the cell. Part of the contractile vacuole complex, often the only part that is visible with the light-microscope. It collects fluid and, periodically, microtubules periodically contract to force this excess water out of the cell, regulating the cell's osmotic balance.

Contractile vacuole complex

An organelle involved in osmoregulation in protist cells, including contractile vacuole, spongiome (a membranous system not usually visible with the light microscope), possibly a pore, collecting canals and ampullae.


Loss of range of motion in a joint due to abnormal shortening of soft tissues.
Stiffening or shortening of muscle caused physiologically and/or by lack of use; results in a reduction of the range of movement of a joint. For example, if an elbow or knee remained bent for extended periods, it could become more and more difficult to straighten.


The contrapositive of A-->B is Not B---->Not A.


Bruising of brain tissue on the side opposite where the blow was struck.

Control specimen

A control specimen is material from a single pool of unknown specimen(s) from which an aliquot is measured every assay run to monitor assay to assay reproducibility and to provide an indirect measurement of the performance of the assay components.


The mass movement of warmed air or liquid to or from the surface of a body or object; Heat transfer through the movement of a fluid, eg: warm air rising.

Convergent evolution

The independent development of similarity between species as a result of their having similar ecological roles and selection pressures. Adaptation for similar function may lead to novel characteristics (homoplasies), which are similar, although they are not inherited from a common ancestor. In some cases, such similarities may be superficial, as in the wings of birds, bats, and insects. In others, similarities can be so striking that it is difficult to determine that the traits arose independently and then later converged upon their current form.

Convergent eye movements

Rotation of the eyes toward each other. Movement of two eyeballs inward to focus on an object moved closer. The nearer the object, the greater is the degree of convergence necessary to maintain single vision.

Convergent series

An infinite series that has a finite sum is called convergent.


The statement made by interchanging the hypothesis and the conclusion of a statement.

Conversion symptom

A loss or alteration of physical functioning that suggests a physical disorder but is actually a direct expression of a psychological conflict or need. The disturbance is not under voluntary control, and is not explained by any physical disorder (this possibility having been excluded by appropriate investigation). Conversion symptoms are observed in conversion disorder, and may occur in schizophrenia.


A set of points such that for any two points in the set, the line segment that connects them is also in the set.

Conveyance loss

water that is lost in transit from a pipe, canal, or ditch by leakage or evaporation. Generally, the water is not available for further use; however, leakage from an irrigation ditch, for example, may percolate to a ground-water source and be available for further use.


Rapidly alternating contractions and relaxations of the muscles, causing irregular movements of the limbs or body generally, and may be accompanied by unconsciousness. They form really only a symptom of some other trouble. The most common cause of convulsions in adults is epilepsy. Convulsions are rarely dangerous to life unless they occur as part of a dangerous condition which is already life threatening


An interaction of the constituent subunits of a protein causing a conformational change in one subunit to be transmitted to all the others.


A set of numbers that identifies the location of a point.

Coordinate systems

A system used to identify locations on a graph or grid; The mathematical description of a geometrical system (detector, magnetic field, etc.) can often be greatly simplified by expressing it in terms of an appropriate coordinate system. Examples of coordinate systems include Cartesian and Euclidean corordinates.


Points that lie within the same plane.


A statement that can be easily proven once a theorem is proved.


convex, transparent coating of the eye (made up of collagen-rich epithelial cells)
which covers the pupil and iris, consisting of five layers allowing light to pass
through to the lens; it is dense, nonvascular, uniform in thickness, and projects
like a dome beyond the sclera; the degree of corneal curvature varies in different
individuals and in the same person at different ages; curvature is more
pronounced in youth than in advanced age.

Cor pulmonale

Failure of the right ventricle resulting from disorders of the lungs or pulmonary vessels causing resistance to the passage of blood through the lungs and pulmonary hypertension.

Corpus callosum

In the vertebrate brain, a tightly packed mass of myelinated nerve fibers connecting the two cerebral hemispheres.

Corpus luteum

A secreting tissue in the ovary that forms from the collapsed follicle after ovulation and produces progesterone. Meaning “Yellow (luteum) body (corpus)”; the progesterone secreting body that is formed on the ovary after ovulation.

Coronary artery disease

The obstruction of the coronary arteries that may be caused by fatty deposits (plaque) or thrombi. Obstruction of the coronary arteries can lead to decreased delivery of oxygen to the heart muscle, and the onset of symptoms.


A substance that causes visible destruction or permanent changes in human skin tissue at the site of contact, e.g. acids and bases.


A statistically-determined connection (relationship) between 2 factors / variables. The correlation coefficient is a a measure of the relation between the statistical distributions of the two random variables.

Correlation coefficient

The quantity r, called the linear correlation coefficient, measures the strength and the direction of a linear relationship between two variables. The linear correlation coefficient is sometimes referred to as the Pearson product moment correlation coefficient in honor of its developer Karl Pearson.
The mathematical formula for computing r is:

where n is the number of pairs of data.
The value of r is such that -1 < r < +1.  The + and – signs are used for positive linear correlations and negative linear correlations, respectively. 
Positive correlation If x and y have a strong positive linear correlation, r is close to +1.  An r value of exactly +1 indicates a perfect positive fit. Positive values indicate a relationship between x and y variables such that as values for x increases,  values for  also increase.
Negative correlation If x and y have a strong negative linear correlation, r is close to -1.  An r value of exactly -1 indicates a perfect negative fit. Negative values indicate a relationship between x and such that as values for x increase, values for y decrease.
No correlation If there is no linear correlation or a weak linear correlation, r is close to 0.  A value near zero means that there is a random, nonlinear relationship between the two variables
Note that r is a dimensionless quantity; that is, it does not depend on the units employed.
A perfect correlation of ± 1 occurs only when the data points all lie exactly on a straight line.  If r = +1, the slope of this line is positive.  If r = -1, the slope of this line is negative. 
A correlation greater than 0.8 is generally described as strong, whereas a correlation less than 0.5 is generally described as weak.  These values can vary based upon the "type" of data being examined.  A study utilizing scientific data may require a stronger correlation than a study using social science data.


The outer, as opposed to the inner, part of an organ. The outer part of the adrenal gland; of the brain

Cortical Blindness

Loss of vision resulting from a lesion of the primary visual areas of the occipital lobe. Light reflex is preserved.

Cortical screw

A screw designed for placement in cortical bone. See cancellous screw.

Corticotrophin releasing hormone (CRH) or Corticotrophin releasing factor (CRF)

A hypothalamic neurotransmitter that controls the secretion of other stress-related hormones in the pituitary. CRF appears to be oversecreted in depression, perhaps contributing to some of the symptoms of depression such as decreased libido, insomnia, and decreased appetite, and CRF also may be involved in anxiety disorders.


A steroid hormone produced by the adrenal gland. Involved in the stress response and increases blood pressure and blood sugar levels; promotes the formation of glucose from protein and fat; also suppresses the inflammatory and immune responses


In a triangle, the cosine of an angle =   (length of the adjacent side)/(hypotenuse).


Artificially constructed cloning vector containing the cos gene of phage lambda: a type of vector used for cloning 35-45 kb of DNA.
These are plasmids carrying a phage l cos site (which allows packaging into l capsids), an origin of replication and an antibiotic resistance gene. A plasmid of 40 kb is very difficult to put into bacteria, but can replicate once there. Cosmids, however, have a cos site, and thus can be packaged into l phage heads (a reaction which can be performed in vitro) to allow efficient introduction into bacteria (you'll have to look up the cos site elsewhere).
Cosmids can be packaged in lambda phage particles for infection into E. coli; this permits cloning of larger DNA fragments (up to 45 kb) than can be introduced into bacterial hosts in plasmid vectors.

Cost of test

The cost of a test is the probability of rejecting good events in hypothesis testing.


A significant decrease ("silencing") in the expression of a gene (within an organism's genome/DNA) that (often) results when man inserts and causes to be expressed a homologous gene. For example, high-oleic oil soybeans result when the GmFad2-1 gene (which codes for native  12 desaturase enzyme) is inserted and expressed in traditional varieties of soybeans. That is because the inserted gene "silences" itself and the endogenous GmFad2-1 gene (i.e., the one naturally/originally present in the soybean plant), which thus prevents formation of the  12 desaturase enzyme (which normally causes most oleic acid within soybeans to be converted into polyunsaturated linolenic acid/linoleic acid).

Coterminal angles

Angles whose measures are 2kpi apart.


The coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient.

Coulomb attraction

Electrostatic attraction between bodies of opposite charge.

Countercurrent flow

A mechanism using the flow of two fluids in opposite directions to concentrate the amount of a chemical or gas in one fluid. This mechanism is used in the loops of Henle in the kidney to concentrate the urine.  It is also the mechanism whereby fish obtain oxygen from the water that flows through their gills. Water flows across the respiratory surface of the gill in one direction while blood flows in the other direction through the blood vessels on the other side of the surface.

Counting numbers

Natural numbers.  The numbers you use to count.

Counts per minute

Counts per minute (CPM) are the number of radioactive disintegrations which were recorded by a detector instrument during one minute.

Coupled reactions

In cells, the linking of endergonic (energy-requiring) reactions to exergonic (energy-releasing) reactions that provide enough energy to drive the endergonic reactions forward.

Covalent bonds

A chemical bond between atoms formed as a result of the sharing of one or more pairs of electrons.
From the L. con, together + valere, to be strong.

CpG island

Short region of DNA in which the frequency of the CG sequence is higher than in other regions. "p" indicates that "C" and "G" are connected by a phosphodiester bond. CpG islands are often located around the promoters of housekeeping genes (which are essential for general cell functions) or other genes frequently expressed in a cell.

Cranial nerves

Nerves of the peripheral nervous system (and therefore nerves connecting to the body) that originate from or terminate in the brain. There are 12 pairs of cranial nerves, all of which pass through foramina of the skull. Cranial nerves are either sensory nerves (containing only or predominately sensory fibers) or mixed nerves (containing both sensory and motor fibers).
(see Spinal Nerves)


The failure of proper fusion of the cephalic part of the neural tube. This leaves the brain and cranium open. The most extreme case results in anencephaly.

Critical point

The point on a curve where the first derivative equals zero.  Extremum.

C-reactive protein

A protein that appears, usually within 24 hours, in the blood during the acute stage of inflammatory disorders such as rheumatic fever, or after a myocardial infarction (heart attack). The serum level of CRP is a sensitive indicator and monitor of rheumatic activity.

CREB-binding protein (CBP)

An acetyltransferase enzyme which regulates genes by activating transcription.

Cre-Lox System

Refers to the use of a particular phage/enzyme system to accomplish a site-specific (on organism's or virus's DNA) insertion or deletion of a specific DNA fragment.
Cre is the name of an enzyme which specifically joins LoxP sites (on DNA molecule) that were earlier engineered into the DNA of both a shuttle vector (i.e., plasmid in this case) and the DNA of the "target" organism or virus.
Certain "knockouts" in transgenic organisms can be created via use of the Cre-Lox System.


A surface with a regularly indented margin.


An adjective used to describe things relating to the twilight associated with sunrise and sundown. An organism is considered to be crepuscular if it is active primarily during the dawn and dusk hours.

Crista (plural = cristae)

An infolding of the inner membrane of a mitochondrion. It houses the electron transport chain and the enzyme catalyzing the synthesis of ATP.

Critical period

A time during the development of an animal when there is maximum plasticity in the evolving neural system, so that it can be most easily modified by environmental inputs.

Crohn’s disease

An inflammatory bowel disease. The two most common forms of inflammatory bowel disease (IBD) are ulcerative colitis and Crohn`s disease. Crohn`s disease can occur anywhere within the digestive tract. While the most common complication of Crohn`s disease is blockage of the intestine, patients also frequently suffer from nutritional complications, and may develop skin problems, inflammation in the mouth or eyes, and diseases of the liver.

Cross fertilization

Fusion of gametes formed by different individuals; as opposed to self-fertilization.

Cross over design

A test in which two drugs (or one drug and placebo) are compared. The patient or animal is started on one treatment, and then after a specified time changed to the other treatment.

Crossing over

The breaking during synapsis of meiosis I, of one maternal and one paternal chromosome, the reciprocal exchange of corresponding sections of DNA between nonsister chromatids, and the rejoining of the chromosomes.
This process can result in an exchange of alleles between chromosomes.

Cross reactivity

A measurement of the reactivity between a binder and a different ligand than the ligand to which the binder is specific.

Cross sectional study

In survey research, a study in which data are obtained only once.
Contrast with  longitudinal studies in which a panel of individuals is interviewed repeatedly over a period of time. Note that a cross sectional study can ask questions about previous periods of time, though.

Crown group

All the taxa descended from a major cladogenesis event, recognized by possessing the clade's synapomorphy.

Cryogenic storage

The preservation of seeds, semen, embryos, or microorganisms at extremely low temperatures, below 130°C. At these temperatures, water is absent, molecular kinetic energy is low, diffusion is virtually nil, and storage potential is expected to be extremely long.


Nineteenth century concept broadly covering small algae, fungi, and bacteria.


Solid substance with a regular geometirc arrangement of atoms.
In biology refers to large, regular assembly of macromolecules such as proteins and nucleic acids. It is possible to isolate and purify proteins or DNA in large quantity and let them crystallize in saturated solution. These protein or DNA crystals contain millions of regularly aligned units that allow the determination of the electron distribution from X-ray diffraction studies. Since atoms are distinguished by their specific numbers of electrons, their distribution allows an analysis of the atomic composition of proteins or DNA. This electron distribution is then used to calculate the so called high resolution structure of molecules.

CT Scan/Computerized Axial Tomography

A series of X-rays taken at different levels of the brain that allows the direct visualization of the skull and intracranial structures.A scan is often taken soon after the injury to help decide if surgery is needed. The scan may be repeated later to see how the brain is recovering.


Pertaining to a system for measuring Conductivity (a measurement of salinity), Temperature and Depth (determined from pressure measurements). Additional parameters, such as pH and dissolved oxygen concentration, can be measured if optional sensors are installed. Often has Niskin bottles attached for taking water samples at specific depths


A solid figure with six square faces.

Cubic feet per second (cfs)

a rate of the flow, in streams and rivers, for example. It is equal to a volume of water one foot high and one foot wide flowing a distance of one foot in one second. One "cfs" is equal to 7.48 gallons of water flowing each second. As an example, if your car's gas tank is 2 feet by 1 foot by 1 foot (2 cubic feet), then gas flowing at a rate of 1 cubic foot/second would fill the tank in two seconds.

Cubic polynomial function

A polynomial of degree 3.

Cued speech

A communication method used by people with hearing disorders, which combines hand signals (cues) with speech-reading. Gestures provide additional information regarding sounds not identifiable by lip reading.

Culture medium

A nutrient system for artificially growing bacteria or other cells: The liquid that covers cells in a culture dish and contains nutrients to nourish and support the cells.
Culture medium may also include growth factors added to produce desired changes in the cells.


A highlight appearing in a data field that indicates you can modify this field, on a dot plot, a crosshair for drawing a polygon gate, on histograms: a line separating regions on single parameter histograms that are treated statistically separate.

Curve fit

Curve fit algorithms are mathematical formulas which compute a continuous curve function using discrete coordinate points.


the movement or flow of electric charges.

Cushing's syndrome

A hormonal disorder caused by prolonged exposure of the body's tissues to high levels of the hormone cortisol. Sometimes called "hypercortisolism," it is relatively rare and most commonly affects adults aged 20 to 50.

Cutaneous sensations

Sensations transmitted using specific sensors in the skin, the mucous membranes and deeper connective tissue layers (also tendons, muscular coats, periosteum) and which encompass the 3 sensory modalities, touch, heat and pain.


Photosynthetic, oxygen-producing bacteria (formerly know as blue-green algae).


A condition in which a lack of oxygen in the blood causes the blood to be darker and the skin to look bluish.


Sweetener which is 30 times sweeter than sucrose, calorie free and heat stable and works synergistically with other sweeteners.

Cyclic AMP

Cyclic adenosine monophosphate, a ring-shaped molecule made from ATP. It is a common intracellular signaling molecule (second messenger) in eukaryotic cells, for example, in vertebrate endocrine cells. It is also a regulator of some bacterial operons.

Cyclic electron flow

A route of electron flow during the light reactions of photosynthesis that involves only photosystem I and produces ATP but not NADPH or oxygen.


A regulatory protein whose concentration fluctuates cyclically.

Cyclin dependent kinase (Cdk)

A protein kinase that is active only when attached to a particular cyclin.


Accelerator in which particles move in spiral paths.

Cyclotron resonance

Phenomenon that occurs when the frequency of revolving ions induced by a specific magnetic field intensity is similar to the frequency of that magnetic field and parallel to it. In these instances, energy may be transferred to the ions, affecting cell metabolic activities.


The union of all line segments that connect corresponding points on congruent circles in parallel planes.

Cystic fibrosis

A common fatal hereditary disease that usually appears early in childhood, in which there is production of a very thick mucus that interferes with normal digestion and breathing. Mutations in the CFTR gene (Transmembrane conductance regulator gene) cause a fundamental disorder of the exocrine glands, especially pancreatic enzyme deficiency and mucus accumulation in the airways.
Because CF symptoms are not always the same, it is often mistaken for diseases such as asthma, allergy, chronic bronchitis, malabsorption, or celiac disease. Due to lung problems, children with CF commonly suffer from anorexia and decreased calorie intake. When combined with poor nutrient absorption, these factors often result in growth failure. Both parents must be carriers of this disease in order for it to be passed onto a child. Currently there is no test to determine if a person is a carrier.


An iron-containing protein, a component of electron transport chains in mitochondria and chloroplasts.

Cytochrome c

Small heme protein in mitochondria. An essential component of the electron transfer chain that transforms energy in food into the energy-rich molecule ATP


A large class of glycoproteins similar to lymphokines but produced by nonlymphocytic cells such as normal macrophages, fibroblasts, keratinocytes, helper T cells and a variety of transformed cell lines. They participate in regulating immunological and inflammatory processes, and can contribute to repair processes and to the regulation of normal cell growth and differentiation.
Although cytokines are not produced by glands, they are hormonelike in their intercellular regulatory functions. They are active at very low concentrations and for the most part appear to function nonspecifically. For example, the cytokines stimulate the endothelial cells to express (synthesize and present) P-selectins and E-selectins on the internal surfaces (of blood vessels). These selectins protrude into the bloodstream, which causes passing white blood cells (leukocytes) to adhere to the selectins, then leave the bloodstream by "squeezing" between adjacent endothelial cells. Cytokines are exemplified by the interferons.


The division of the cytoplasm to form two separate daughter cells immediately after mitosis


A class of related plant hormones that retard aging and act in concert with auxins to stimulate cell division, influence the pathway of differentiation, and control apical dominance.

Cytomegalovirus (CMV)

Any of a group of DNA viruses causing the enlargement of the epithelial cells, especially the salivary glands, and associated with pneumonia and with abnormalities in newborn infants that affect various organs, resulting in mental retardation and other diseases.


Part of the food ingestion structures (mouth) of some cells. Usually a channel of microtubules that draws newly formed food vacuoles away from the cytostome and into the cell.


The entire contents of the cell, exclusive of the nucleus, within which organelles occur and which is bounded by the plasma membrane.

Cytoplasmic determinants

In animal development, substances deposited by the mother in the eggs she produces that regulate the expression of genes affecting the early development of the embryo

Cytoplasmic streaming

A circular flow of cytoplasm, involving myosin and actin filaments, that speeds the distribution of materials within cells


Found in some ciliates, the site at which old food vacuoles fuse with the cell surface, and undigested residues are excreted.


A pyrimidne base (nitrogenous base) and constituent of nulceotides and as such one member of the base pair G-C (guanine and cytosine).


Literally “cell skeleton”; an integrated intracellular  fibrous network of microfilaments, microtubules, neurofilaments, intermediate filaments and an assortment of proteins that branch throughout the cytoplasm within eukaryotic cells, used to provide shape to a cell or to create tracts along which cellular organelles may be moved. The cytoskeleton acts like scaffolding, anchoring internal cell structures and give the cell a definite structure and internal spatial organization, and maintains this structure, allowing the cell to modify its appearance during development, growth or injury. It also functions in cell movement and division motility, and may assist in communication with other cells and the environment. Red blood cells, for instance, would be spherical instead of flat if it were not for their cytoskeleton.
The three major fiber types are made up of different proteins: microfilaments are made up of actin protein, intermediate filaments are made up of various kinds of proteins (e.g. keratin), and microtubules made up of tubulin. The three fiber types serve different functions; actin filaments are often associated to changes in cell size and structure, contractility such as in muscle cells, and cell division, growth and motility. Microtubules are major filaments for internal transport and movement of chromosomes and organelles during cell division. Intermediate filaments contribute to flexibility, elasticity, and stiffness of cells and tissues.


The semifluid portion of the cytoplasm.


Literally, 'the cell mouth'. only used in reference to organisms which ingest food at one or more particular locations, and then best used in reference to the region(s) of the cell surface through which food gains entry into the cell; part of the 'mouth' structures.
See also Cytopharynx

Cytotoxic or killer T cells  

A type of lymphocyte that kills infected cells and cancer cells. T cells that destroy body cells infected by viruses or bacteria; also attack bacteria, fungi, parasites, and cancer cells and will kill cells of transplanted organs if they are recognized as foreign.