Search for a word or term

Word / term



A mobile-carrier calcium ionophore (allows Ca+2 ions to cross cell membranes).
Originally isolated as an antibiotic from Streptomyces chartreusensis.

A band

Region of a sarcomere where actin and myosin filaments overlap; corresponds to the darker stripes of striated muscle

ABC proteins

Proteins that contain the ATP-binding cassette (“ABC”) motif. They include several types of transporters of molecules.
Consists of 3 separate trans-membrane proteins. The ligand-binding domain is usually restricted to a single type of molecule. ATP bound to its domain provides energy to pump ligand across membrane

ABCD rating

A classification (“staging”) system for prostate cancer that uses the letters A, B, C and D to denote different degrees of cancer spread.
“A” and “B” refer to cancer that is confined to the prostate. “C” refers to cancer that has grown out of the prostate but has not spread to lymph nodes or other places in the body. “D” refers to cancer that has spread to lymph nodes or to other places in the body.

Abdominal Muscles

Muscles of the abdomen which aid in respiration

Abdominopelvic Cavity

A ventral cavity consisting of the abdominal cavity (between the diaphragm and the level of the pelvic bone) and the pelvic cavity (between the top of the pelvis and pubic area). Ex. The intestines and stomach are found in the abdominopelvic cavity


Movement of a bone, and the limb of which it is a part, away from the mid-line of the body. Abduction is the opposite movement to adduction. E.g., Raise your arm upwards and away from your body
Hence, Abductor: Any muscle that moves one part of the body away from another - or away from the midline of the body


Rare genetic disorder of fat metabolism that interferes with the normal absorption of fat and fat soluble vitamins from food.
Characterized by severe deficiency of beta-lipoproteins and abnormal red blood cells (acanthocytes) and abnormally low cholesterol levels.

Ab initio gene prediction

A computing biology technique that attempts to identify genes without any knowledge of their function nor of the genetics of the organism.
This can be accomplished because different gene components, such as exonsintrons, promoters, polyadenylation signals etc are associated with unique patterns in the DNA sequence.


Of or pertaining to the nonliving, specifically, the nonliving components of an ecosystem,
Examples = temperature, humidity, the mineral content of the soil, etc.

Abiotic factors

The chemical and physical environmental factors in ecosystems.


1. Experimental: removal or killing of some part of an organism; for example, in experimental embryology, used to determine what effect absence of the structure will have on development of the remaining embryo.
2. In medicine, the removal or destruction of a body part or tissue or its function. Ablation may be performed by surgery, hormones, drugs, heat, radiofrequency, or other methods.
Ablation experiment = an experiment designed to produce an animal deficient in one or a few cell types, in order to study cell lineage or cell function. The idea is to make a transgenic mouse with a toxin gene (often diphtheria toxin) under control of a specialized promoter which activates only in the target cell type. When embryo development progresses to the point where it starts to form the target tissue, the toxin gene is activated, and that specific tissue dies. Other tissues are unaffected.


Relating to position: away from the mouth
See Adroal


Not normal. Deviating from the usual structure, position, condition, or behavior. In referring to a growth, abnormal may mean that it is cancerous or premalignant (likely to become cancer ).

Abnormal failure

An artificially induced failure of a component, usually as a result of "abnormals" testing for regulatory agency safety compliance.

ABO blood group

Classification of red blood cells based on the presence or absence of A and B carbohydrate antigens.

Abortive transduction

The failure of a transducing DNA segment to be incorporated into the recipient chromosome.


An enclosed collection of pus in tissues, organs, or confined spaces in the body.


The x-axis or x-coordinate. The abscissa of the point (a, b) is a.

Absolute Pressure

Gage pressure plus atmospheric pressure.

Absolute Pressure Transducer

A transducer that has an internal reference chamber sealed at or close to 0 psia (full vacuum) and normally provides increasing output voltage for increases in pressure.

Absolute value

The distance of a number from zero, expressed as a positive value ignoring the sign of that distance.
The absolute value of -4 is 4 (i.e., you take the value of the distance of the number from 0, and ignore the fact that here the distance is a negative value).
The absolute value of the calculation 4-6 is not -2 but 2 (i.e., again you ignore the sign of the distance of the number, namely -2, from 0).

Absolute zero

The lowest theoretical temperature at which thermal energy is at a minimum and where all molecular activity ceases.
Defined as 0o Kelvin, calculated to be -273.15 °C or -459.67°F.

Absorbance or Optical density

A measure of the amount of light absorbed by a solution.
Absorbance is equal to the logarithm of the ratio of incident light to transmitted light.

Absorbance optics

Optical method for measuring the concentration of a substance by measuring the loss of light due to absorbance of photons by molecules.

Absorption (in digestion)

A process by which nutrients move from the lower digestive tract (small and large intestine or colon) into the blood stream to be utilized by the body.

Absorption (in spectroscopy)

The interaction between atoms and radiation (light, X-rays, UV, infrared), where some of the energy of the radiation is absorbed by the electrons of the atoms, increasing their energy content.
The loss of intensity of the radiation (e.g. reduced light intensity) can be measured and is an indicator of the structural state of the molecules that absorb the radiation.

Absorption (of water vapour)

Retention (of water vapor) by penetration into the bulk of a material.

Absorption spectrum

The range of a pigment's ability to absorb various wavelengths of light.

Absorptive endocytosis

Internalization of a protein by a cell after the protein has bound weakly and nonspecifically to charged groups at the cell surface.

Abstract Concept

A concept or idea not related to any specific instance or object and which potentially can be applied to many different situations or objects.
Persons with cognitive deficits often have difficulty understanding abstract concepts.

Abstract intelligence / reasoning

The intellectual ability to understand relationships and to react, not only to concrete objects, but also to concepts, ideas, images, and symbols that are more intangible objects.

Abstract thinking

Being able to apply abstract concepts to new situations and surroundings


Absence or inability to exercise will-power or to make decisions. Also, slow reaction, lack of spontaneity, and brief spoken responses.
Usually associated with damage to a cerebellar vessel.

Abzyme (also known as Catalytic enzyme)

An antibody selected for its ability to catalyze a chemical reaction by binding to and stabilizing the transition state intermediate.


The inability to perform simple problems of arithmetic


1. Disability characterized by difficulties with phrasing and sentence structure of speech.
2. Inability to express ideas logically.


The rate of change of velocity; the first derivative of velocity with respect to time.
If position is represented by s(t), then velocity is s’ (t) and acceleration is s"(t).
Units expressed in "g".

Accelerator Mass Spectrometry

An ultra sensitive quantitative technique for measuring isotopic ratios.
It is typically used for determining the ratio of the abundant to rare isotopes of certain elements. Can measure ratios as low as 1 in 1015 for carbon. Its advantages include using small samples, fast analysis time and it is far more sensitive than all other mass spectrometry techniques


A transducer which converts mechanical motion into an electrical signal that is proportional to the acceleration value of the motion.


The larger of two reactants that interact reversibly to form a complex.

Acceptor arm (of tRNA)

The end of a tRNA molecule to which an amino acid becomes bound.
It contains both the 5' and 3' ends of the tRNA. The 3'-terminal sequence of cytidine-cytidine-adenosine (CCA) overhangs the end, and the terminal A is the site of 'acceptance' of the amino acid.

Acceptor end (of tRNA)

Four nucleotides at the 3' end of tRNA, which form the site at which the amino acid becomes bound.
The last three nucleotides are cytidine-cytidine-adenosine (CCA) and the ribose of the terminal adenosine forms a bond with the amino acid.

Acceptor stem (of tRNA)

That part of the acceptor arm of a tRNA molecule in which nucleotide sequences from the 5f and 3f ends are paired to form duplex RNA

Accessory cell

Cell required for, but not actually mediating, a specific immune response.
Often used to describe antigen-presenting cells (APC).

Accessory organ

An organ that aids in digestion but is not part of the digestive tract such as the liver and pancreas

Access protocol

A defined set of procedures that function as an interface between a user and a network and enable the user to employ the services of that network.

Accidental release

The unintentional discharge of a microbiological agent (i.e., microorganism or virus) or eukaryotic cell due to a failure in the containment system.

Accomodation (in the Action Potential)

An increase in the threshold for an action potential that occurs in some neurons during a slowly developing or prolonged depolarization. The result is that only a few action potentials are generated during prolonged depolarization above the normal threshold level.

Accomodation (in vision)

The process at the eye whereby the lens aacquires greater refractive power to allow near objects to be seen in sharp focus.


To grow by addition as by the adhesion of parts or particles that are normally separate.


The combined error of nonlinearity, repeatability, and hysteresis expressed as a percent of full scale output.

Acesulfame K or acesulfame potassium

A low-calorie sweetener.
An organic salt consisting of carbon, nitrogen, oxygen, hydrogen, sulphur and potassium atoms. It is 200 times sweeter than sucrose, has a synergistic sweetening effect with other sweeteners, has a stable shelf-life and is heat stable. It is excreted through the human digestive system unchanged, and is therefore non-caloric.

Acetyl CoA

The entry compound for the Krebs cycle in cellular respiration.
Formed from a fragment of pyruvate attached to a coenzyme


neurotransmitter (a chemical agent used for transmitting nerve impulses across synapses which are points of functional contact between a nerve and another cell.)

Acid dyes

Dyes that are anionic or have negatively charged groups such as carboxyl.


a sour tasting, corrosive substance - the opposite of a base substance.  Acidic solutions will turn a litmus red.

Acid-fast staining

Histological staining procedure that differentiates between bacteria based on their ability to retain a dye when washed with an acid alcohol solution

Acellular vaccine

Vaccine consisting of antigenic parts of cells.

Acentric chromosome

Applied to a chromatid or a chromosome when it lacks a centromere.
This condition may arise in an inversion heterozygote as a result of crossing over between a normal and an inverted segment that does not include the centromere.

Acentric fragment

A chromosomal piece without a centromere.


A class of artificial sweeteners derived from oxathiazinone; some varieties are over a hundred times sweeter than table sugar (sucrose).


A term used to describe a molecule which, in a given configuration, is superimposible on its mirror image.
This is in contrast to chiral molecules which cannot be superimposed on their mirror images.


Pertaining to substances that increase the relative number of hydrogen ions (H+) in a solution.
Having a pH less than 7; acidic; opposite of alkaline/basic.

Acid-base reaction

A reaction between an acid and a base, resulting in the generation of a conjugate base and a conjugate acid.

Acid ionization constant (Ka)

The degree to which an acid ionizes; Ka = ( [H3O+] [Ac¯] ) / [HAc]

Acid phosphatase

An enzyme found primarily in the prostate and semen.
Increased blood serum levels may indicate cancer of the prostate or may follow prostatic massage.


An abnormal increase in acidity of body fluids caused by acid buildup or bicarbonate depletion; A condition in which blood is more acidic than usual

Acidic oxide

An oxide that reacts with water to produce an acid.
Nonmetal oxides are acidic, e.g. CO2 + H2O → H2CO3

Acinar cells

Spindle shaped cells of the pancreas that secrete hydrolase enzymes which break down peptidesdisaccharides and triglycerides


The small gas exchange regions of the lung.

AC Linearity

A dynamic measurement of how well an A/D (analog-to-digital converter) performs.
In an ideal A/D converter, a pure sine wave on the analog input appears at the digital output as a pure (sampled) sine wave. In the real world, however, spurious signals due to nonlinear distortion within the A/D appear in the digital output. These anomalies are usually combinations of harmonics of the fundamental and intermodulation products, produced when the fundamental and its harmonics beat with the sampled frequency.


A skin inflammation affecting approximately 80% of those between the ages of 12 and 24.
Located in each hair follicle or tiny pit in the skin is a gland that lubricates the skin. If some oil gets trapped in the gland, bacteria multiply in the pit and the skin becomes inflamed.


Animals that lack a coelom (body cavity)


Greater than normal hearing sensitivity

Acoupedic method

A technique of teaching hearing impaired children to speak and use their hearing.
It emphasizes auditory training begun early and used alone rather than combined with visual training.


The nature, cause, and phenomena of the vibrations of elastic bodies; which vibrations create compressional waves or wave fronts which are transmitted through various media, such as air, water, wood, steel, etc.


Acequias are gravity-driven waterways, similar in concept to a flume. Most are simple ditches with dirt banks, but they can be lined with concrete. They were important forms of irrigation in the development of agriculture in the American Southwest. The proliferation of cotton, pecans and green chile as major agricultual staples owe their progress to the acequia system.

Acquired immunodeficiency syndrome (AIDS)  

A collection of disorders that develop during the late stages of infection by the human immunodeficiency virus (HIV), defined by a specified reduction of T cells and the appearance of characteristic secondary infections.
The HIV attacks helper T cells, crippling the immune system and greatly reducing the body's ability to fight infection. Thus AIDS generally results in premature death brought about by various diseases that overwhelm the compromised immune system

Acquisition time

This term relates to sampling A/Ds (analog-to-digital converters) which utilize a track/hold amplifier on the input to acquire and hold the analog input signal. Acquisition time is the time required by the T/H amplifier to settle to its final value after it is placed in the track module.

Acre foot

The volume of water required to cover 1 acre of land (43,560 square feet) to a depth of 1 foot. Equal to 325,851 gallons or 1,233 cubic meters.


A chromosome whose centromere divides the chromosome into a long arm and a short arm.


Excessive growth.
Occurs due to the production of excessive growth hormone by the pituitary gland

Acromioclavicular Dislocation

Disruption of shoulder ligaments of the normal joint between the acromion and the clavicle.

Acrosomal vesicle

Membrane-bound organelle in the head of a sperm that is derived from the golgi apparatus.
The vesicle contains enzymes that digest proteins and complex sugars in the outer coverings of an egg. Fusion of the acrosomal vesicle with the plasma membrane of the sperm (in the "acrosome reaction") exposes receptors that bind to the egg surface and is necessary for fertilization.


A protrusion like a cap on the anterior end of a sperm cell. Contains digestive enzymes that enable the sperm to penetrate layers around the oocyte.

Acrosome reaction

The exposing of the acrosome as the sperm reaches the zona pellucida of the ovum so that enzymes may be released in order for the walls of the ovum to be penetrated and fertilization to be accomplished

Acrylamide gels

A polysaccharide gel used to measure the size of nucleic acids (in bases or base pairs).
This is the gel of choice for DNA or RNA in the range of thousands of bases in length, or even up to 1 megabase if you are using pulsed field gel electrophoresis.


A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.
Hence: Actin Filaments - thin filaments; form part of the contractile filaments in muscle


Group of gram-positive bacteria containing the actinomycetes and their high G 1 C relatives.


Aerobic, gram-positive bacterium that forms branching filaments (hyphae) and asexual spores.

Action Potential

A rapid series of changes in the resting membrane potential (RMP) of a neuron or muscle cell, caused by stimulus-triggered, selective opening and closing of voltage-sensitive gates in Sodium and Potassium ion channels and, in some cells, involving other ions such as Calcium.
The AP is produced in response to a stimulus or input that causes the RMP to reach a threshold level. If this is reached, the Action Potential (AP) occurs, commencing with a depolarization phase when the RMP becomes progressively less negative and eventually goes past (overshoots) 0 milliVolts to reach a positive value (i.e., the inside of that point of the cell membrane now becomes positively charged compared to the outside).  This is followed by a repolarization phase where the membrane potential returns to its resting value (i.e.,  the inside of that point of the cell membrane once again is negatively charged compared to the outside), an undershoot phase  when the membrane potential may transiently become more negative than the resting level, and finally by a gradual return of the membrane potential to the resting level.
As noted above the AP is produced if the RMP reaches a threshold level. At this threshold level, voltage-gated Na+ channels open allowing an influx of Na+ ions down its electrochemical gradient, thereby causing the depolarization phase. Repolarisation occurs when these channels close and voltage-gated K+ channels open to allow the efflux of K+ down its electrochemical gradient and (generally) this is also responsible for the undershoot. An active Na+/K+ ion pump (see Primary Active transport systems: ATPase-ion pumps) is responsible for re=establishing the resting membrane potential by re-establishing the resting ionic concentrations.
Note that there are many nuances of this basic description of the factors underlying an AP, e.g., in cardiac cells Ca++ ions play a role in maintaining a plateau of depolarisation, etc.

Action Potential propagation

The process by which an action potentialspreads throughout a neuron

Activated support

A support matrix capable of covalently binding a molecule.

Activation energy

Energy needed to initiate a chemical reaction.

Activation energy constant, E

Temperature coefficient determined from the slope of a ln (k) versus 1/TA plot.

Activation volume constant, V

Pressure coefficient obtained from the slope of the ln (k) versus a pressure difference (PPR) plot.


In biological terms, this means that energy is required for the specific process under consideration

Active expiration

The forceful expelling of the air from the lungs (such as during coughing)

Active filter

An active filter is one that uses active devices such as operational amplifiers to synthesize the filter response function.
This technique has an advantage at high speeds because the need for inductors is eliminated.

Active immunity

Immunity generated by an organism's production of antibodies and cytokines

Active site

The part of a protein that must be maintained in a specific shape if the protein is to be functional, for example, the part to which the substrate binds in an enzyme.
e.g., The part of the receptor for a chemical; The part of an enzyme where the actual enzymatic function is performed; The specific portion of an enzyme that attaches to the substrate by means of weak chemical bonds..

Active transport

Systems to move substances across the cell membrane, with the expenditure of energy to overcome an unfavourable thermodynamic potential (i.e., to move substances against concentration or electrochemical gradients, with the help of energy input and specific transport proteins).
See Primary (Direct) Active Transport and Secondary Active Transport.

Active zones

Specialized areas in the presynaptic nerve terminal (the terminal of the nerve fibre arriving at a synapse) critically involved in release of neurotransmitter.
Active zones are the sites where calcium enters the nerve terminal and the presynaptic vesicles containing neurotransmitter fuse with membrane to release neurotransmitter

Active immunity

Immunity generated by production of antibodies and cytokines.

Activity based proteomics (or Activity based protein profiling)

A functional proteomic technology that uses specially designed chemical probes that react with mechanistically-related classes of enzymes.
The basic unit of ABPP is the probe which typically consists of two elements: a reactive group (RG) and a tag. Additionally, some probes may contain a binding group which enhances selectivity. The reactive group usually contains an electrophile that gets covalently-linked to a nucleophilic residue in the active site of an active enzyme. An enzyme that is inhibited by enzyme inhibitors or post-translational modifications will not react with an activity-based probe. The tag may be either a reporter such as a fluorophore or a handle such as biotin or an alkyne or azide for use with the Huisgen 1,3-dipolar cycloaddition (also known as click chemistry).

A major advantage of ABPP is the ability to monitor enzyme activity directly, rather than being limited to protein or mRNA abundance. With classes of enzymes such as the serine proteases and metalloproteases that often interact with endogenous inhibitors or that exist as inactive zymogens, this technique offers a valuable advantage over traditional techniques that rely on abundance rather than activity.

Finally, in recent years ABPP has been combined with tandem mass spectrometry enabling the identification of hundreds of active enzymes from a single sample. This technique, known as ABPP-MudPIT is especially useful for profiling inhibitor selectivity as the potency of an inhibitor can be tested against hundreds of targets simultaneously.

Activity group therapy

A group-oriented approach used for treatment of young people with behavior disorders.


Of abrupt onset, in reference to a disease. Acute often also connotes an illness that is of short duration, rapidly progressive, and in need of urgent care.

Acute angle

A positive angle that measures less than 90 degrees.

Acute exposure

An intense exposure over a relatively short period of time.

Acute Lymphocytic Leukemia (ALL)

A disorder of blood-cell production in which abnormal white blood cells accumulate in the blood and bone marrow.

Acute / Adult Respiratory Distress Syndrome (ARDS)

A life threatening problem in which the lungs are severely injured. Inflammation occurs throughout the lungs. In the lung tissue small blood vessels leak fluid and the alveoli collapse or fill with fluid, disrupting lung function.
The causes of ARDS are not well understood. It develops from a sudden injury, either direct or indirect. Examples of common direct injuries include: pneumonia, inhaling one’s vomit, breathing in harmful fumes or smoke, and chest trauma, for example, a severe blow to the chest or other accident that bruises the lungs. Examples of common injuries that are “indirect” (associated with problems occurring in other parts of the body) include: sepsis (severe and widespread bacterial infection in the body), severe injury to the body that causes a low blood pressure, bleeding that requires blood transfusions, and pancreatitis (inflammation of the pancreas).
(Source: American Thoracic Society, Patient Information Series: Acute Respiratory Distress Syndrome (ARDS))

Acute triangle

A triangle each of whose angles measures less than 90 degrees.

Acute schizophrenia

A type of schizophrenia characterized by the sudden onset of symptoms, often associated with confusion, perplexity, ideas of reference, emotional turmoil, excitement, depression, fear of dreamlike dissociation.


Describing a state in which the female is not experiencing ovarian cycles


A product of fatty acid activation.
Acyl-CoA is subsequently carried by carnitine into the mitochondria for beta-oxidation. All of this is done in the context of fat breakdown for energy usage.


Change in a organism resulting from natural selection; a structure which is the result of such selection; A genetically determined characteristic that enhances the ability of an organism to cope with its environment.
A process in biological evolution as the result of natural selection where a species becomes better adjusted to the living conditions of its environment (temperature, food sources, and predators). In adaptation, individuals that have the most offspring contribute more of their genetic makeup to the next generation. Beneficial traits are favored in this editing process and the next generation of a species or population (for instance a smaller geographical subset of a species) is better adapted to new environmental conditions that caused certain individuals to have fewer offspring. Thus genes that are not optimal for certain conditions will become rarer as a result. Adaptation, as evolution in general, is studied at the level of a population of interbreeding individuals.

Adaptation traits

Complex of traits related to reproduction and survival of the individual in a particular production environment.
Adaptation traits contribute to individual fitness and to the evolution of animal genetic resources. By definition, these traits are also important to the ability of the animal genetic resource to be sustained in the production environment.

Adaptive / assistive equipment

A special device which assists in the performance of self-care, work or play/leisure activities or physical exercise.

Adaptive fit

Compatibility between demands of a task or setting and a person's needs and abilities.

Adaptive landscape or Adaptive surface

The surface plotted in a three-dimensional graph, with all possible combinations of allele frequencies for different loci plotted in the plane, and mean fitness for each combination plotted in the third dimension.

Adaptive peak

An equilibrium state in a population when the gene pool has allele frequencies that maximize the average fitness of a population's members.

Adaptive radiation

The divergence of several new types of organisms from a single ancestral type.

A/D Converter (Also A/D or ADC)

Short for analog-to-digital converter. Converts real-world analog signals into a digital format that can be processed by a computer.

Addison’s disease

A rare disease where the adrenal glands do not make enough cortisol and/or aldosterone (adrenal hormones).
There are different causes of Addison’s disease, but in many cases your body’s immune system may not recognize the adrenal gland and try destroy it.

Addition line

A line of individuals or cells carrying additional chromosomes or parts of chromosomes.
Hence: Alien addition line = Addition line with foreign additional chromosomes

Additive genetic effects

When the combined effects of alleles at different loci are equal to the sum of their individual effects.

Additive genetic variance

Genetic variance associated with the average effects of substituting one allele for another.

Additive identity

The number zero is called the additive identity because when you add it  to a number, N, the result you get is the same number, N.

Additive inverse

The additive inverse of a number, N, is the number that when you add it to N, the result that you get is zero.  The additive inverse of 7 is -7. The additive inverse of -3 is 3.

Additive model (in genetics)

A mechanism of quantitative inheritance in which alleles at different loci either add a fixed amount to the phenotype or add nothing.

Address (in computing)

The label or number identifying the memory location where a unit of information is stored.


Movement of a bone, and the limb of which it is a part, towards the mid-line of the body.
Hence, Adductor: Any muscle that moves one part of the body towards another - or towards the midline of the body.


One of the four nitrogen-containing bases occurring in nucleotides (which are used to make up DNA and RNA).
Adenine is also the base in the energy carrying molecule ATP (adenosine triphosphate) which is the energy store of cells.


A form of cancer that develops from a malignant abnormality in the cells lining a glandular organ such as the prostate.
Almost all prostate cancers are adenocarcinomas

Adenosine deaminase deficiency

A severe immunodeficiency disease that results from a lack of the enzyme adenosine deaminase.
It usually leads to death within the first few months of life.

Adenosine mono- / di- / tri- phosphate (AMP / ADP / ATP)

A nucleotide consisting of adenine, ribose, and one (mono), two (di) or three (tri) phosphate groups.
ATP releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.
ADP formed by the removal of one phosphate from an ATP molecule.
AMP, in its cyclic form (cyclic AMP, cAMP) functions as a "second messenger" for a number of vertebrate hormones and neurotransmitters.

Adenosine diphosphate (ADP)

A lower energy store in living systems; consists of a nucleotide (with ribose sugar) with two phosphate groups with energy stored in the phosphate bonds
ADP (adenosine diphosphate) is the product after breaking down ATP to ADP, releasing energy for cellular processes.

Adenosine triphosphate (ATP)

A common form in which energy is stored in living systems; consists of a nucleotide (with ribose sugar) with three phosphate groups, with energy stored in the phosphate bonds.
ATP (adenosine triphosphate) is the energy store of cells. The energy is stored in the phosphate bonds so that breaking down ATP to ADP (adenosine diphosphate) releases energy for cellular processes and then breaking down ADP to AMP (adenosine monophosphate) releases some more energy. Almost all caloric content of food is converted into ATP before it can be utilized for tissue growth, muscle work and other physiological processes.
ATP synthase = An enzyme that allows protons to move through the mitochondrial membrane and trigger phosphorylation of ADP to ATP.


A group of DNA-containing viruses of the Adenoviridae family.
This group of viruses can cause infections in the eye and upper respiratory tract. Conditions caused by the virus include the common cold, pneumonia and bronchitis. Adenoviruses used in gene therapy are altered to carry a specific tumor-fighting gene.
Adenoviruses can also be genetically modified and used in gene therapy to treat cystic fibrosis, cancer, and potentially other diseases.

Adenylyl cyclise

An enzyme that converts ATP to cyclic AMP in response to a chemical signal.

Adhesion molecule

A glycoprotein molecular "chain" that protrudes from the surface membrane of certain cells, and causes cells (possessing "matching" adhesion molecules) to adhere to each other.
From the Latin adhaerere = "to stick to".
Adhesion molecules also play a crucial role in guiding monocytes to sources of infection (e.g., pathogens) because adhesion molecules in the walls of blood vessels (after activation caused by pathogen invasion of adjacent tissue) adhere to like adhesion molecules in the membranes of monocytes in the blood. The monocytes pass through the blood vessel walls, become macrophages, and fight the pathogen infection (e.g., triggering tissue inflammation, etc.).

Adiabatic system

A system that neither gains or loses heat.

Adiabatic compression

Compression or decompression processes occurring without heat transfer.


Cell laden with fat.


A chemical substance produced by fat cells that signals to other cell types in the body.

Adipose tissue

Tissue consisting of cells laden with lipid.
Tissue composed predominantly of fat cells (adipocytes)


The amount of a person’s body mass that is made up of fat


Absence of drinking or abnormal avoidance of drinking.

Adjacent angles

Two angles that share both a side and a vertex.

Adjacent segregation

In a reciprocal translocation heterozygote during meiosis the segregation of a translocated and a normal chromosome together, giving unbalanced gametes with duplications and deficiencies leading to non-viable zygotes.
Adjacent segregation is of two kinds depending on whether non-homologous (adjacent-1) or homologous (adjacent-2) centromeres segregate together.
Adjacent-1 segregation is the usual type of adjacent segregation, consisting of segregation of non-homologous centromeres during meiosis in a reciprocal translocation heterozygote such that unbalanced gametes with duplications and deficiencies are produced.
Adjacent-2 segregation is rare, consisting of the segregation of homologous centromeres during meiosis in a translocation heterozygote such that unbalanced gametes with duplications and deficiencies are produced.


Substance or treatment given after the primary treatment to increase the chances of a cure.
Adjuvant therapy may include chemotherapy, radiation therapy, hormone therapy, or biological therapy. One common example is the use of agents given with a vaccine which then boost the effects of the vaccine, either through its own effects on the innate immune system or by assisting in the delivery of the vaccine to the target.

Adjusted age

Age in weeks from conception. Computed by adding number of weeks from conception to birth and number of weeks from birth to date of computation.
Used with premature infants.

Adjusted coefficient of variation (CV)

The adjusted CV is the coefficient of variation (standard deviation/mean) of the adjusted responses from replicate samples.

Adjusted response (in assasys)

The raw response of a sample, adjusted to remove signal variation. It is a measurement of the total ligand binding of the sample.
The adjusted response is obtained by multiplying the raw response times the multiplying factor for that assay run. The multiplying factor is calculated by dividing the relative activity entered in Test Method Setup by the average of the tracer activity raw responses. By adjusting the tracer activity (sometimes termed total count in isotopic assays) to the relative activity, signal variation (differences from assay run to assay run due to decay, enzyme/substrate deterioration, instrument drift, etc.) can be factored out from binding variation, (differences from assay run to assay run due to binder deterioration, incubation differences, buffer changes, etc.). An arbitrary value (relative activity) is entered to which the average tracer activity's response will be adjusted. This value is defaulted to 100,000 CPM for isotopic and chemiluminescent assays, and to 2 for colorimetric test methods.  If tracer activity samples are assayed, StatLIA will adjust all raw responses to this value to remove signal variation. These adjusted responses will then be used for all computations.. If tracer activity samples are not assayed, no adjustment will be performed and the raw responses will be used for all computations.

Adjusted variance

The variance of the mean of the adjusted responses from replicate samples.

Adjustment disorder

Maladaptive reaction in adolescents to an identifiable source.


The form of DNA at high humidity.
It has tilted base pairs and more base pairs per turn than does B DNA.


Relating to position: toward the mouth

ADP Kinase

An enzyme that catalyzes the first step of the pathway for histidine biosynthesis in Salmonella typhimurium.
ATP reacts reversibly with 5-phosphoribosyl-1-pyrophosphate to yield N-1-(5'-phosphoribosyl)-ATP and pyrophosphate.

Adrenal cortex

The outer portion of the adrenal gland.
The adrenal cortex produces steroid hormones, which regulate carbohydrate and fat metabolism, and mineralocorticoid hormones, which regulate salt and water balance in the body.

Adrenal glands

Paired two-part glands that sit atop the kidneys in mammals.
Composed of two glandular portions: an outer cortex, which responds to endocrine signals in reacting to stress and effecting salt and water balance, and a central medulla, which responds to nervous inputs resulting from stress.
Produces catecholamines, mineralocorticoids, glucocorticoids, and sex hormones.


A hormone, produced by the medulla of the adrenal gland.
It increases the concentration of glucose in the blood, raises blood pressure and heartbeat rate, and increases muscular power and resistance to fatigue; also a neurotransmitter across synaptic junctions.

Adrenal insufficiency

A condition where the adrenal glands do not make enough cortisol and/or aldosterone (adrenal hormones).

Adrenal medulla

The inner portion of the adrenal gland.
The adrenal medulla produces adrenaline and noradrenaline, as part of the stress response of the body.

Adrenocorticotropin (ACTH)

Hormone produced by the anterior pituitary gland.
Stimulates the production of cortisol by the adrenal cortex.

Adsorption (of water vapor)

Retention (of water vapor) as a surface layer on a material


The mature stage of an organism, usually recognized by the organism's attaining the ability to reproduce.

Adult stem cell

A specialized cell that is needed for growth, wound healing and tissue regeneration. Adult stem cells are found in all tissues and organs of animals and plants.


Organism, especially a Gram E bacterium that requires oxygen to live.
Such organisms are capable of growing in normal air, equivalent to 20% oxygen, or in aerated liquids containing dissolved oxygen. Many aerobes are equally able to grow in the absence of oxygen. These are termed facultative anaerobes.


Containing oxygen.
Referring to an organism, environment, or cellular process that requires oxygen.

Aerobic plate count

Method for determining the presence and concentration of aerobic bacteria in food products.

Aerobic respiration or aerobic metabolism

A chemical process in which oxygen is used to make energy from carbohydrates.
Glucose is converted into CO2 and H2O in the presence of oxygen, releasing large amounts of ATP. This process includes the Krebs cycle, electron transport chain, and oxidative phosphorylation.

Aestivation (or aestivate, estivate, estivation)

In animals: a state of dormancy/inactivity during the summer.
In plants: the arrangement of sepals and petals or their lobes in an unexpanded flower bud.

A factor

A protein which is found in the bacterial genus Streptomyces that helps start the production of streptomycin and the process of morphological differentiation.
It is used in biotechnology to induce these functions in mutant strains of Streptomyces that can't produce it themselves.

Affect (as in affective disorders)

The observable emotional condition of an individual at any given time. An immediately expressed and observed emotion. A feeling state becomes an affect when it is observable, for example, as overall demeanor or tone and modulation of voice.
Affect is to be distinguished from mood, which refers to a pervasive and sustained emotion. Common examples of affect are euphoria, anger and sadness.
Hence affective = Related to or arising from feelings, emotions, or attitudes.

Affected relative pair

Individuals related by blood, each of whom is affected with the same trait.
Examples are affected sibling, cousin, and avuncular pairs.

Affective disorder

A disorder of mood (feeling, emotion).
Refers to a disturbance of mood and other symptoms that occur together for minimal duration of time and are not due to other physical or mental illness.
affective = Related to or arising from feelings, emotions, or attitudes.
(see Affect)


Bringing inward to a central part or region.
Term applied to nerves and to blood vessels to describe the direction in which the contents of the structure (nerves / blood vessels) are being carried relative to another (centrally located) structure.

Afferent arteriole

Branches of the renal artery that approach the proximal portion of a nephron.


A measure of the intrinsic binding strength of the ligand binding reaction.
he intrinsic attractiveness of the binder for the ligand is typically expressed as the equilibrium constant (Ka) of the reaction. The equilibrium constant Ka = [Ligand-Binder]/[Ligand][Binder], where [ ] represents the molar concentration of the material at equilibrium.


Dangerous poisons produced by moulds of the Aspergillus species, found in cereals, oilseeds and nuts when incorrectly dried and stored.


A gelatinous material prepared from certain red algae that is used to solidify nutrient media for growing microorganisms.
Used as a medium to grow microorganisms.

Agarose gels

A polysaccharide gel used to measure the size of nucleic acids (in bases or base pairs).
This is the gel of choice for DNA or RNA in the range of thousands of bases in length, or even up to 1 megabase if you are using pulsed field gel electrophoresis.

Aggregated data

Data that have been combined from smaller units into a larger unit.
Often carried out to preserve confidentiality, e.g., in the case of a census data from individuals are aggregated to give population values from which individuals cannot be identified.

Aggregation technique

A technique used in model organism studies in which embryos at the 8-cell stage of development are pushed together to yield a single embryo (used as an alternative to microinjection).


A region of the cell where protein aggregates collect.


The process of becoming older, a process that is genetically determined and environmentally modulated.


A drug which binds to a receptor and activates it, producing a pharmacological response (contraction, relaxation, secretion, enzyme activation, etc.).


Failure to recognize familiar objects although the sensory mechanism is intact.
May occur for any sensory modality.


Inability to express thoughts in writing.


Inability to recognize letters traced on the skin.


Natural bacterium often used for gene transfer in plants such as soy, tobacco or tomatoes. Agrobacterium tumefaciensA common soil bacterium that causes crown gall disease by transferring some of its DNA to the plant host. Scientists alter Agrobacterium so that it no longer causes the disease but is still able to transfer DNA. They then use this altered Agrobacterium to ferry desirable genes into plants.

AIDS-related complex

A condition in which antibody tests for AIDS virus are positive and patients may exhibit enlarged lymph nodes, fatigue, fever, night sweats, weight loss, and unexplained diarrhea, but do not have any of the more serious complications of AIDS.

Air-bone gap (in hearing thresholds)

The number of deciBels by which air-conduction thresholds in an ear exceed bone conduction thresholds in the same ear.
Generally measured using pure tones. When the difference averages 10 or more dB it indicates conductive pathology (i.e., problems with the external or middle ears that conduct sound energy to the inner ear).

Air embolism

Blockage of a blood vessel by a bubble of air that has entered the bloodstream


Advanced Interactive Executive: IBM's version of UNIX.


Motor restlessness ranging from a feeling of inner disquiet (often localized in the muscles) to an inability to sit still or lie quietly; a side effect of some antipsychotic drugs.


Absence of movement.

Akinetic seizure

A seizure that is evidenced by an absence or poverty of repetitive or clonic movements.

Alagille Syndrome

A rare inherited liver disorder seen in infants and young children.
The disease is characterized by a buildup of bile in the liver due to a deficiency or absence of normal bile ducts inside the liver and a narrowing of bile ducts outside the liver. Symptoms of the disorder can include jaundice, stunted growth, fatty deposits in the skin, facial deformities, and abnormalities in the heart, eyes, vertebrae, and kidneys.


A recently-proposed term to describe a group of structurally diverse multifunctional host proteins that are rapidly released following pathogen challenge or cell injury and, most importantly, are able to both chemotactically recruit and activate dendritic antigen-presenting cells.
These potent immunostimulants, including defensins, cathelicidin (LL37), eosinophil-derived neurotoxin (EDN), lactoferrin (LF), granulysin, high-mobility group box protein 1 (HMGB1) and HMGN1 serve as early warning signals to activate innate and adaptive immune systems. They interact with chemokine-like receptors and activating receptors on host cells. For example, some beta defensins, LL37, HMGB1 and EDN mimic chemokine and cytokine activities by interacting with CCR6, FPRL-1, RAGE and Toll-like receptors (TLR2) respectively. These proteins also are antimicrobial peptides (AMP's) and are constitutively produced and released by leukocytes, but can also be induced by injurious stimulants and cytokines. In addition they are produced by keratinocytes and epithelial cells lining the gastro-intestinal, genito-urinary and tracheobronchial tree. These AMP's all induce the maturation of myeloid dendritic cells and have in vivo immunoadjuvant effects.


A pigmentless white phenotype, determined by a mutation in a gene coding for a pigment-synthesizing enzyme.


A group of relatively small proteins that are soluble in water and readily coagulated by heat.

Alcoholic fermentation

An anaerobic step that yeast use after glycolysis that breaks down pyruvic acid to ethanol and carbon dioxide.


A steroid (mineralocorticoid) released from the adrenal cortex that maintains salt and fluid balance in the body.
It acts on the distal tubules of the kidney to stimulate the reabsorption of sodium (Na+) and the passive flow of water from the filtrate. The end result of its release is an increase in blood pressure.


See:Naproxen .


Inability to read.


Unicellular or multicellular photosynthetic eukaryotes that generally lack roots, stems, leaves, conducting vessels, and complex sex organs.
A polyphyletic grouping of organisms with chloroplasts. Now divided into blue-green algae (eubacteria), cryptomonads, chlorarachniophytes, glaucophytes, dinoflagellates and other alveolates, euglenids (a group of Euglenozoa), various stramenopiles (also referred to as chromophytes, chrysophytes, heterokonts - including the diatoms and brown algae), haptophytes (= prasinophytes), green algae (green plants), and red algae.


Compound which is extracted from algae and used in puddings, milk shakes and ice cream to make these foods creamier and thicker and to extend shelf life.


A step-by-step problem-solving procedure, especially an established, recursive (repetitive) computational procedure for solving a problem in a finite number of steps.


Used in the context of processing digitized signals (e.g. audio) and images (e.g. video), aliasing describes the effect of undersampling during digitization which can generate a false (apparent) low frequency for signals, or staircase steps along edges (jaggies) in images.
In a sampled data system, the analog input must be sampled at a rate of at least twice the bandwidth of the signal in order to avoid loss of data (Nyquist Theorem). Adhering to the Nyquist Theorem prevents in-band "alias" signals, which are beat frequencies between the analog signal and the sampling clock that inherently occur. Aliasing can be avoided by an antialiasing (analogue) low-pass filter, before sampling. The term antialiasing is also in use for a posteriori signal smoothing intended to remove the effect.

Aliased Imaging

This is a technique, commonly applied to Direct Digital Synthesis, for using intentional aliasing as a source of high-frequency signals.


Anterior lumbar interbody fusion. An operation for stabilization of the spine using an anterior approach. This is the standard approach for inserting cages in the lumbar disc spaces.


Pertaining to substances that increase the relative number of hydroxide ions (OH–) in a solution.
Having a pH greater than 7; opposite of acidic.


Alkali (also known as a base) has less free hydrogen ions (H+) than hydroxyl ions (OH-). a substance having marked basic properties (i.e. substance with properties of a base).

Alkaline phosphatase

An enzyme found mainly in liver and bone.
Blood serum alkaline phosphatase is usually measured to detect liver or bone disease.


A condition in which blood is more basic than usual.

Alkylating agent

A chemical agent that can add alkyl groups (for example, ethyl or methyl groups) to another molecule.
Many mutagens act through alkylation.


Extra-embryonic membrane emerging as a sac from the hindgut's ventral wall; formed from the splanchnopleure (combination of endoderm and splanchnic mesoderm).
Found in amniotes, it is one of the four extraembryonic membranes (chorion, amnion, allantois and yolk sac) that are adaptations of the terrestrial egg. It collects waste materials from the embryo, and as a part of the chorio-allantoic membrane can be a site of gas exchange.


The genetic variant of a gene; Alternative form of a genetic locus. One of the different forms of a gene that can exist at a single locus.
One of two or more alternative nucleotide sequences at a single gene locus which occurs on either of two homologous chromosomes in a diploid organism. A gene can be found in different variants in a population, even in the same individual. Alleles are responsible for the different traits of certain characteristics, such as eye and hair color in animals, and flower and seed color in plants. Example: at a locus for eye color the allele might result in blue or brown eyes. Alleles are also responsible for genetic diseases

Allele frequency

A measure of how common an allele is in a population; the proportion of all alleles at one gene locus that are of one specific type in a population.
Often called gene frequency.

Allele specific hybridization

Usually refering to when probes anneal specifically to a certain allele.

Allele specific polymerase chain reaction (AS-PCR)

Amplification of specific alleles, or DNA sequence variants, at the same locus.
Specificity is achieved by designing one or both PCR primers so that they partially overlap the site of sequence difference between the amplified alleles.

Allelic exclusion

A process whereby only one immunoglobulin light chain and one heavy chain gene are transcribed in any one cell; the other genes are repressed.


Part of a food (a protein) that stimulates the immune system of food allergic individuals.
A single food can contain multiple food allergens. Carbohydrates or fats are not allergens. Most common food allergens are nuts (especially peanuts), egg, milk, histamine, etc.

Allergenic reaction

An inflammatory response triggered by a weak antigen (an allergen) to which most individuals do not react.
Involves the release of large amounts of histamine from mast cells.

Allergy mediator

Biochemical, such as histamine and heparin, that mast cells release when contacting an allergen, causing allergy symptoms.


1. Variation in alleles among members of the same species. 2. Taken from different individuals of the same species.
e.g., Allogeneic antigen: Genetic variations of the same antigens within the same species.
Allogeneic graft: Grafts between two or more people allogeneic at one or more loci (usually with reference to histocompatibility loci).
Allogeneic bone marrow transplantation: A procedure in which a person receives stem cells (cells from which all blood cells develop) from a genetically similar, but not identical, donor.
Allogeneic stem cell transplantation: A procedure in which a person receives blood-forming stem cells from a genetically similar, but not identical, donor. This is often a sister or brother, but could be an unrelated donor.

Allometry or Allomteric growth

Phenomenon whereby parts of the same organism grow at different rates.
The variation in the relative rates of growth of various parts of the body, which helps shape the organism.

Allopathic medicine

A system in which medical doctors and other healthcare professionals treat symptoms and diseases using drugs, radiation, or surgery.

Allopatric speciation

Speciation in which the evolution of reproductive isolating mechanisms occurs during physical separation of the populations.


Polyploid produced by the hybridization of two species.
A common type of polyploid species resulting from two different species interbreeding and combining their chromosomes.

All-or-none event

An action that occurs either completely or not at all, such as the generation of an action potential by a neuron.

Allosteric transition or Allosteric change

Alteration of a protein conformation resulting in alteration of function (e.g. non-competitive receptor inhibition).

Allosteric protein

A protein whose shape is changed when it binds a particular molecule.
In the new shape the protein's ability to react to a second molecule is altered.

Allosteric site

A specific receptor site on an enzyme molecule remote from the active site.
Molecules bind to the allosteric site and change the shape of the active site, making it either more or less receptive to the substrate.


Element with more than one natural form


The protein product (or the result of its activity) of an allele which may be detected as an antigen in another member of the same species.(eg histocompatibility antigens, immunoglobulins), obeying the rules of simple Mendelian inheritance.


A substance formed by the combination of two or more elements, at least one of which must be a metal.
Alloy 11: A compensating alloy used in conjunction with pure copper as the negative leg to form extension wire for platinum-platinum rhodium thermocouples Types R and S.


Deposits of clay, silt, sand, gravel, or other particulate material that has been deposited by a stream or other body of running water in a streambed, on a flood plain, on a delta, or at the base of a mountain.


Homozygosity in which the two alleles are alike but unrelated.


Form of an enzyme that differ in amino acid sequence from other forms of the same enzyme, and all encoded by one allele at a single locus.
The differences are shown by electrophoretic mobility or some other property.

Ally methyl trisulfide, dithiolthiones

Type of sulfide/thiol found in cruciferous vegetables which may provide the health benefits of lowering LDL cholesterol and of maintaining a healthy immune system.


Type of carotenoid found in carrots which provides the health benefit of neutralizing free radicals that may cause damage to cells.

Alpha-fetoprotein (AFP)

A substance produced by the fetus that is found in fetal serum, amniotic fluid, and the mother's bloodstream.
Elevated levels of AFP may indicate that the baby has a neural tube defect such as spina bifida (incomplete closure of the spinal column) which can lead to paralysis of the lower limbs, repeated urinary tract infections, mental retardation or hydrocephalus ("water on the brain"). It is also a useful nonspecific tumor-associated antigen (tumor marker).

Alpha helix

A spiral shape constituting one form of the secondary structure of proteins, arising from a specific hydrogen-bonding structure.
This helical, usually right-handed, arrangement of a polypeptide chain is a common secondary structure in proteins. It has maximal intra-chain hydrogen bonding.

Alpha spasticity

A tonic contraction of one muscle or a group of synergistic muscles at a joint caused by excitation of alpha motoneurons innervating the muscle.


Chemical name for the vitamin E form with the highest biological activity. Several other tocopherols
and tocotrienols also have vitamin E activity.

Altered specificity or Relaxed specificity or Star activity

Under extreme non-standard conditions, restriction endonucleases are capable of cleaving sequences which are similar but not identical to their defined recognition sequence.
This activity may be a general property of restriction endonucleases and any restriction endonuclease may be made to cleave noncanonical sites under certain extreme conditions. The manner in which an enzyme's specificity is altered depends on the enzyme and on the conditions employed to induce the star activity. The most common types of altered activity are single base substitutions, truncation of the outer bases in the recognition sequence, and single-strand nicking.

Alternate segregation

At meiosis in a reciprocal translocation heterozygote, the passage (segregation) of both normal chromosomes to one pole and both translocated chromosomes to the other pole, giving genetically balanced gametes.
Segregation of centromeres during meiosis in a reciprocal translocation heterozygote such that genetically balanced gametes are produced.

Alternative splicing

Various ways of splicing out introns in eukaryotic pre-mRNAs resulting in one gene producing several different mRNAs and protein products.
The same pre-mRNA molecule, which consists of introns and exons, is spliced in different ways to produce mature mRNAs of different lengths and different functionality.


The perpendicular distance from the base of a figure to the highest point of the  figure.

Alu family

A dispersed intermediately repetitive DNA sequence found in the human genome in about three hundred thousand copies.
The sequence is about 300 bp long. The name Alu comes from the restriction endonuclease AluI that cleaves it.

Alveolus (pl. Alveoli)

1. One of the dead-end, multilobed air sacs that constitute the gas exchange surface of the lungs.
2. One of the milk-secreting sacs of epithelial tissue in the mammary glands.

Alzheimer’s Disease

A neurodegenerative disease that causes progressive memory loss and severe dementia in advanced cases. Alzheimer’s Disease is associated with certain abnormalities in brain tissue, involving a particular protein, beta-amyloid. The gene encoding amyloid has been located and cloned from chromosome 21.AD) is a devastating neurodegenerative disease which shows the clinical symptoms of memory loss, cognitive decline, and behavioural changes. AD is an age-associated disease; the prevalence of AD increases with age, from 6% of the population aged 65 years and over, to over 40% of individuals aged 85 years and over. Diagnosis of AD is confirmed post mortem by neuropathological examination. The main neuropathological features of AD are: neurofibrillary tangles (NFT) caused by a hyperphosphorylation of the microtubule-associated protein tau, formation of extracellular deposits of β-amyloid termed senile plaques, reactive astrocytosis, granulovacuolar degeneration, and neuronal loss. The last-mentioned is related to the clinical symptoms of memory loss, cognitive decline, and behavioural changes through the disruption of synaptic connectivity. No cure has yet been found, and current treatment is associated with modest symptomatic improvement in some patients. Alzheimer pathology is not distributed uniformly throughout the brain. Certain areas are more susceptible to the proteinaceous aggregations of β-amyloid in extracellular plaques and hyperphosphorylated tau in intraneuronal neurofibrillary tangles (NFTs), the loss of synapses and neurones, and the reactive proliferation of astrocytes. These major hallmarks of Alzheimer pathology are progressive in severity, but not all are in synchrony with the advance of clinical symptoms. Loss of synapses and synaptic proteins measured post mortem show the closest correlation with declining ante mortem cognitive test scores. Accumulating NFT pathology correlates with cognitive decline but β-amyloid (Aβ) plaque load does not. A major aim of this project is to contrast different aspects of Alzheimer pathologies in both spared and susceptible regions of the brain and to compare the severity of the pathologies with cognitive test scores and the rates of decline. The region-specific loss of synapses could be the substrate for the cognitive decline and neuropsychiatric symptoms of AD.

Glutamate is the predominant excitatory neurotransmitter in the brain and operates in more than
70% of synapses, including afferents to hippocampal and neocortical pyramidal neurons, the major neurone classes lost in AD 7. Three vesicular glutamate transporter isoforms (VGLUT1–3) have been cloned and characterised; specific antibodies are available. VGLUT1 and 2 divide distinct subpopulations of excitatory synapses 8. VGLUT3 overlaps in distribution with the other two isoforms, and colocalises with markers of cholinergic and serotonergic synapses in some areas. The VGLUTs are ideal choices as markers of glutamatergic terminals. Significantly lower VGLUT1, but not VGLUT2, immunoreactivity has been reported in parietal and occipital cortical regions of AD brain that correlated with NFT load, a marker of pathological severity 10. The decline in VGLUT1 and 2 was also correlated with Clinical Dementia Rating (CDR) score in the prefrontal dorsolateral cortex in AD cases 11. There was a further reduction of VGLUT1 levels in cases with comorbid depression. Immunohistochemical (IHC) studies of the VGLUTs will help to determine whether these proteins are lost from otherwise intact glutamatergic terminals.
The major inhibitory neurotransmitter in the brain, γ-amino butyric acid (GABA), is packaged into presynaptic vesicles by the vesicular inhibitory amino acid transporter (VIAAT). This transporter has not been studied in AD, but Aβ1–40 was found to reduce the levels of VIAAT in hippocampal cell culture, reflecting the decrease in GABAergic input despite more, albeit shorter, dendrites. VIAAT complements the VGLUTs and serves as an excellent marker of presynaptic inhibitory terminals.

Excitatory synapse formation and maintenance may be of particular importance to the clinical symptoms, damage, and/or regrowth of synapses in AD. N-cadherin belongs to a large family of cell adhesion proteins. It is implicated in neurite outgrowth, synaptic junctional complex formation, and maintenance of the synapse. It is located both in the presynaptic terminal and on the postsynaptic membrane, and colocalises with synaptophysin, synapsin I, PSD95, and GluR1.

Immunological staining of N- (“neural”) and E- (“epithelial”) cadherin is mutually exclusive; some synapses are negative for both. In cultured hippocampal cells, N-cadherin segregates from general to excitatory synapses during maturation, suggesting that it would be a good candidate as an excitatory synaptic marker. In AD, N-cadherin is associated at the synaptic junction with presenilin1 (PS1), a protein encoded by the most commonly mutated gene in familial AD. In cultured cells, mutant forms of PS1 suppress N-cadherin-based cell-cell adhesion by subcellular misplacement. β-catenin binds to N-cadherin and mediates its interaction with the cytoskeleton. β-catenin has a multifaceted rôle not only in synapse formation but also in activation of transcription factors through the Wnt signaling pathway. β-catenin is reportedly associated with PS1 and GSK3, a kinase involved in the putative hyper-phosphorylation of tau to form NFTs. N-cadherin and β-catenin levels were higher in AD than controls. Excitatory synaptic terminals in adult mammalian CNS are held in place by an asymmetric junctional complex. The protein PSD–95 (SAP90) binds to the NR1 subunit of the glutamate-NMDA receptor. It has been implicated in the assembly of some of the components of the postsynaptic density (PSD) and in receptor targeting and localization. PSD95 levels are reportedly lower in AD superior temporal cortex than in controls, a finding replicated in our laboratory (see results to date). EAAT3 is a glutamate transporter located on the postsynaptic membrane. Reports on the levels of EAAT3 in AD are conflicting. One study reported no loss of EAAT3 in AD frontal cortex, while another study showed an accumulation of detergent-insoluble EAAT3 in AD hippocampus. Together with the following markers of excitatory postsynaptic terminals, EAAT3 is a good candidate for study. A tubulin binding protein, gephyrin, is associated with glycine and GABA receptors and anchors them in clusters at the postsynaptic membrane. Gephyrin levels are significantly reduced in AD. Aberrant levels of these proteins could alter the glutamate and/or GABA receptor populations at the postsynaptic terminal.

Amber codon

The codon UAG, a nonsense codon.

Amber suppressor

A mutant allele coding for a tRNA whose anticodon is altered in such a way that the suppressor tRNA inserts an amino acid at an amber codon in translation suppressing (preventing) termination.

Ambiguous Genitalia

A birth defect that causes a baby’s genitals to look different from a typical boy or girl making it hard to tell the sex of the baby. X
Additional lab and/or xray testing will be needed to confirm if baby is a boy or a girl.


Loss of vision due to an imbalance of eye muscles.


To walk.


The lack of menstrual cycles in females.
There are two types:
Primary Amenorrhea: lack of first cycle or period after age 16 years.
Secondary Amenorrhea: missed cycles or periods for longer than 6 months for girls of any age.
Idiopathic Hypothalamic Amenorrhea: Thought to be due to an aberration at the level of the hypothalamus, but the exact cause is unknown.

American Academy of Orthopaedic Surgeons

The professional organization of American orthopaedists. Literally, the practice of child straightening, orthopaedics is the branch of surgery that is broadly concerned with the skeletal system (bones).

American Sign Language (ASL) (nickname = Ameslan)

A visual language (uses hand gestures) for persons who are deaf or hearing impaired.
It contains its own vocabulary, grammar, idioms, and syntax It's vocabulary and grammar differ from the English language. ASL is the most common form of sign language used in the United States. Also referred to as "sign language".

Ames test

A widely used test to detect possible chemical carcinogens; based on mutagenicity in the bacterium Salmonella.

Amino acids

Any of a class of 20 small, nitrogen-containing molecules that are linked together to form proteins; Building block of proteins and enzymes.  
These are the building blocks of proteins. They themselves are relatively small molecules (normally less than 10 carbon atoms) characterized by possession of an amino group (- NH2) and a carboxylic acid group (-COOH) and a side chain (R - of a number of different kinds) attached to the same carbon atom. They are soluble in water.
Dietary proteins need to be broken into their amino acid components before they can be used by the body. Note that there are 20 amino acids found in proteins. Many nutritional lists describe only 18 occluding glutamine and asparagine. Their values are included in those reported for the acidic forms glutamate and aspartate.


Transfer RNA (tRNA) molecule with its cognate amino acid attached.
Aminoacyl-tRNA synthetase is the enzyme that attaches an amino acid to its cognate tRNA(s).


A class of antibiotics specific for gram negative bacteria.

Amino group

A functional group that consists of a nitrogen atom bonded to two hydrogen atoms; can act as a base in solution, accepting a hydrogen ion and acquiring a charge of +1.

Aminoacyl—tRNA synthetases

A family of enzymes, at least one for each amino acid, that catalyze the attachment of an amino acid to its specific tRNA molecule.


A device used to measure electrical current, which is measured in amperes (A, or amps)


The process by which decomposers break down proteins and amino acids, releasing the excess nitrogen in the form of ammonia (NH3) or ammonium ion (NH4+).


Partial or complete loss of memory; Lack of memory about events occurring during a particular period of time.


A method of prenatal testing in which amniotic fluid is withdrawn from the uterus through a needle.
The fluid and the fetal cells contained in the amniotic fluid are analyzed to detect biochemical or chromosomal disorders.


A prenatal diagnostic procedure in which X-ray of the mother's uterus, after injection of a radiopaque substance, allows visualization of the fetus, the placenta, and the uterine lining.
This may be used to confirm a diagnosis of neural tube defects.


Tthe innermost membranous sac enclosing the embryo of an amniote.
One of the four amniote extraembryonic membranes, derived from the somatopleure (combination of ectoderm and somatic mesoderm). It becomes filled with amniotic fluid in which the embryo is suspended.


A prenatal diagnostic procedure in which the fetus is seen by use of a fibre optic light.

Amniotic fluid

Fluid that surrounds and protects the developing fetus.


Any organism in a polyphyletic grouping of organisms which move and feed using pseudopodia.


Like an amoeba; Having no definite shape to the cell, able to change shape.
Usually means that the organism has the capacity to produce pseudopodia.


A mutant showing the complete lack of some normal substance or structure.


An allopolyploid; a polyploid formed from the union of two separate chromosome sets and their subsequent doubling.
An organism produced by hybridization of two species followed by chromosome doubling. An allotetraploid that appears to be a normal diploid.


Containing both polar and nonpolar domains.
Thus the molecule has both a hydrophilic region and a hydrophobic region.


Organisms capable of gaining energy and nutrients by both autotrophic and heterotrophic means. (Same as amphizoic).


Capable of donating and accepting protons, thus able to serve as an acid or a base


The product of PCR or LCR; a piece of DNA that has been synthesized using amplification techniques.


Amplification is the use of substances which directly increase the amount of signal measured in proportion to the quantity of analyte.

Amplification (of DNA)

The production of many DNA copies from one or a few copies.
An increase in the number of copies of a specific DNA fragment; can be in vivo or in vitro.

Amplified fragment length polymorphism (AFLP)

A highly sensitive method for detecting polymorphisms in DNA.
Following restriction enzyme digestion of DNA, a subset of DNA fragments is selected for PCR amplification and visualisation.


A piece of electronic equipment that increases (amplifies) the signal by an adjustable factor.
The amount by which an amplifier boosts the signal is called the gain of the amplifier.


Upper region of the mammalian oviduct, near the ovary.
Fertilization typically takes place in this region.


The enlarged bases of the semicircular canals in the inner ear, lined with hair cells that detect fluid movement and convert it into action potentials.


An almond-shaped complex of many nuclei located in the middle of the brain.
Connected to the hippocampus, it plays a role in emotionally laden memories. It contains a huge number of opiate receptor sites implicated in rage, fear and sexual feelings. It is part of the limbic system.


A digestive enzyme produced largely by the pancreas and salivary glands that converts starches to sugars.
Abnormally high levels of amylase in the blood or urine may be found in patients with inflammation of the pancreas or salivary glands (mumps)


A protein that tends to accumulate and aggregate to form plaques in the brain cells of patients with Alzheimer's disease.
See Amyloidosis.


A group of diseases in which protein is deposited in specific organs (localized amyloidosis) or throughout the body (systemic amyloidosis).
May be either primary (with no known cause) or secondary (caused by another disease, including some types of cancer). Generally, primary amyloidosis affects the nerves, skin, tongue, joints, heart, and liver; secondary amyloidosis often affects the spleen, kidneys, liver, and adrenal glands.

Amyotrophic Lateral Sclerosis (ALS)

A disease condition with selective death of large caliber axons in the spinal cord.
Neurofilament accumulation occurs. 2% of cases have SOD1 mutations that probably act through a toxic property, not loss of activity. It maybe due to misfolding of SOD1.

Anabolic reactions  

Reactions in cells in which new chemical bonds are formed and new molecules are made.
Generally require energy, involve reduction, and lead to an increase in atomic order.

Anabolic steroids

Synthetic chemical variants of the male sex hormone testosterone.
They produce increased muscle mass but also suppress testosterone production, leading to shrinkage of the testes, growth of the breasts, and premature baldness; long-term use increases the risk of kidney and liver damage and of liver cancer.


Biosynthesis of molecules in cells and part of metabolism.
Within a cell or organism, the sum of all biosynthetic reactions (that is, chemical reactions in which larger molecules are formed from smaller ones).


Organism, especially a bacterium that does not require oxygen or free oxygen to live.
Some of these organisms may also be able to grow in oxygenated conditions (facultative aerobes), whereas others cannot tolerate oxygen and are killed when exposed to air. Such organisms are termed obligate anaerobes.


Lacking oxygen.
Referring to an organism, environment, or cellular process that lacks oxygen and may be poisoned by it.
Hence Anaerobic respiration = Cellular respiration in the absence of oxygen.


Evolutionary change along an unbranching lineage; change without speciation.

Analogous structure

Body part in different species that is similar in function but not in structure that evolved in response to a similar environmental challenge.


An analyte is the compound being measured.
In immunoassays, the analyte can be either the ligand or the binder


The third stage of meiosis and mitosis in which sister chromatids (meiosis II) or homologous chromosomes (mitosis and meiosis I) are separated by spindle fibers, and ending when a complete set of daughter chromosomes are located at each of the two poles of the cell.
An intermediate stage of nuclear division during which chromosomes or chromatids are pulled to the poles of the spindle.
Anaphase I = Anaphase of meiosis I, when homologs separate.
Anaphase II = Anaphase of meiosis II, when chromatids separate.

Anaphylactic shock

A severe and sometimes life-threatening immune system reaction to an antigen to which a person has been previously exposed.
The reaction is caused by the release of a flood of histamine into the circulatory system to produce widespread effects which may include itchy skin, oedema, collapsed blood vessels, fainting, difficulty in breathing, and death.


Substance capable of releasing histamine from mast cells.


A term used to describe cancer cells that divide rapidly and have little or no resemblance to normal cells.


local - Anesthesia confined to one part of the body.

Anesthetic (epidural) - An anesthetic injected in the fluid-filled sac (the dura) around the spine, which partially numbs the abdomen and legs.

Anaxonal neuron

Neuron that has no neurites or extremely short ones.
Typically found in sensory systems, such as the vertebrate visual and auditory systems.

Anchondroplastic dwarfism

An inherited form of dwarfism or arrested growth.
It results in overall smallness and especially short upper arms and thighs.


Any organism, population, or species from which some other organism, population, or species is descended by reproduction.


The principal male steroid hormones, such as testosterone, which stimulate the development and maintenance of the male reproductive system and secondary sex characteristics.

Androgen receptor (AR)

Receptors that have binding sites for the steroid androgen.
Androgen receptors are altered in people with spinobulbar muscular atrophy (SBMA)


A biological change characterized by a gradual decline in androgens.
Experienced by men during and after their midlife


Below normal levels of red blood cells or hemoglobin, or both.
It can be caused by many different conditions, including iron deficiency. Symptoms may include fatigue, weakness, headache, and dizziness. Appropriate blood tests will confirm the diagnosis of anemia and shed light on its etiology.


Having an abnormal number of chromosomes.
Aneuploid cells may also have an abnormal DNA content.


A condition in which there is an abnormally low number of red blood cells present in the blood.


A condition in which the person has a partial or complete absence of cerebral tissue.
This condition of forebrain degeneration is caused by failure of anterior neuropore closure and consequent prolonged contact of the forebrain with amniotic fluid. Although infants with this neural tube defect are sometimes born alive, the condition is invariably fatal within a few hours or days.


The condition of a cell or of an organism that has additions or deletions of a small number of whole chromosomes from the expected balanced diploid number of chromosomes.


An abnormal dilation of a blood vessel; A balloon-like deformity in the wall of a blood vessel. The wall weakens as the balloon grows larger, and may eventually burst, causing a hemorrhage.
While the mechanical pressure of an aneurysm on surrounding tissue can lead to a number of difficulties, the greatest risk to health is due to an aneurysm`s potential to rupture, thrombose, or embolize. A ruptured aneurysm can cause a stroke, or even death.

Angel dust or Phencyclidine hydrochloride (PCP)

An anesthetic agent used in veterinary medicine.
Also an illegal hallucinogenic street drug, "angel dust." Its presence may be detected by urine testing.


The formation of new blood vessels.

Angiogenetic clusters (Also known as “Blood islands”)

Masses of splanchnic mesodermal cells found in the yolk sac of amniotes.
The first blood forming tissue of the embryo, responsible for red blood cells and vitelline blood vessels.


A procedure to enlarge the opening in a blood vessel that has become narrowed or blocked by plaque.
Examples of angioplasty are balloon angioplasty and laser angioplasty.


The union of two rays with a common endpoint.


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

Angiotensin II

A hormone that acts to increase blood pressure.


An abnormal deficiency of sweat.

Ankle sprain

Stretching and slight or partial tearing of one or more ligaments in the ankle.

Ankylosing / ankylosis

Undergoing ankylosis (stiffening or fusion of a joint ).

Ankylosing spondylitis

A type of arthritis that causes chronic inflammation of the spine and the sacroiliac joints. Chronic inflammation in these areas causes pain and stiffness in and around the spine. Over time, chronic spinal inflammation (spondylitis) can lead to a complete cementing together (fusion) of the vertebrae, a process called ankylosis. Ankylosis causes total loss of mobility of the spine.


Embryonic primordium from which a specific part of the organism develops.
The rudimentary basis of an organ in an embryo.


Spontaneous alignment of two complementary single polynucleotide (RNA, or DNA, or RNA and DNA) strands to form a double helix.


A ringlike structure, or any body part that is shaped like a ring. Applied to many small ring-shaped structures.


A positively charged electrode. Attracts negatively charged ions.


Inability to recall names of objects.
Persons with this problem often can speak fluently but have to use other words to describe familiar objects.


An absence of the eyeball.


An abnormal loss of the appetite for food.
Anorexia can be caused by cancer, AIDS, a mental disorder (i.e., anorexia nervosa), or other diseases.
Anorexia nervosa: An eating disorder marked by an intense fear of gaining weight, a refusal to maintain a healthy weight, and a distorted body image. People with anorexia nervosa have an abnormal loss of appetite for food, try to avoid eating, and eat as little as possible.


Loss of sense of smell.

ANOVA (Analysis of variance)

A statistical test to examine the effect of more than one independent variable on more than one dependent variable, and to see if there are any interactions between the independent variables.
Analysis of variance (ANOVA) is a statistical test which compares the distribution of two or more sample groups to determine if one or more of the groups are significantly different from the others. The sample groups must be gaussian in distribution. In an analysis of variation, the average variance within each of the sample groups is factored out from the variance between each of the sample groups before computing the probability of significant differences between the groups.


A lack of oxygen.
Cells of the brain need oxygen to stay alive. When blood flow to the brain is reduced or when oxygen in the blood is too low, brain cells are damaged.

Antagonist (drug or chemical)

A drug which attenuates the effects of an agonist.
Antagonism can be competitive and reversible (i.e. it binds reversibly to a region of the receptor in common with the agonist.) or competitve and irreversible (i.e.antagonist binds covalently to the agonist binding site, and no amount of agonist can overcome the inhibition). Other types of antagonism are non-competitive antagonism where the antagonist binds to an allosteric site on the receptor or an associated ion channel.

Antagonistic muscles  

A pair of muscles that work to produce opposite effects.
One contracts as the other relaxes, e.g., the bicep and tricep muscles on opposite sides of the upper arm


The hypothesis of conditional statement.  The "if" part of an "if-then" statement.
What precedes.

Anterior fontanelle

The membrane-covered space on the top of the head; also called the soft spot.
It generally closes over by 18 months of age.

Anterograde Amnesia

Inability to consolidate information about ongoing events. Difficulty with new learning.


Type of flavonoid found in various fruits which provides the health benefits of neutralizing free radicals and possibly reducing the risk of cancer.


A disease caused by the bacterium Bacillus anthracis, which can be used as a lethal biological weapon.
Anthrax may occur in three forms:

  1. Cutaneous (skin) - occurs when the bacterium enters a cut or abrasion on the skin, e.g., when handling the infected animals.
  2. Gastrointestinal - occurs after eating contaminated food.
  3. Inhalation - occurs by inhaling the bacterial spores.

Bacillus anthracis is a Gram-positive bacterium which contains two major virulence factors: poly-D-glutamic acid capsule and anthrax toxin.  The poly-D-glutamic acid capsule is nontoxic by itself, but plays an important role in protecting the organism from being killed by phagocytes.  Anthrax toxin consists of three distinct proteins: lethal factor, oedema factor, and protective antigen.  The lethal factor is a protease that cleaves members of the mitogen-activated protein kinase kinase (MAPKK) family, thereby interrupting the signaling pathways. The edema factor is an adenylate cyclise.  The protective antigen mediates the delivery of these two enzymatic components by binding to a cellular receptor.

The Bacillus anthracis spore is quite stable and can exist in soil for many years. However, naturally occurring anthrax is very rare.  The bacterial spores usually clump together and are hard to suspend in air.  To make them deadly, they have to be separated and combined with fine dust particles to increase the time of floating in air.


Caused by, or as a result of, human activity


A higher primate; includes monkeys, apes, and humans.


Substance produced by bacteria or fungi that destroys or prevents the growth of other bacteria and fungi.
An antimicrobial compound produced by living micro-organisms, used therapeutically or sometimes prophylactically in the control of infectious diseases. Over 4,000 antibiotics have been isolated, but only about 50 have achieved wide use. Antibiotics are not effective against viruses.

Antibiotic resistance

The ability of a microorganism to produce a protein that disables an antibiotic or prevents transport of the antibiotic into the cell.
Plasmids generally contain genes which confer on the host bacterium the ability to survive a given antibiotic. If the plasmid pBR322 is present in a host, that host will not be killed by (moderate levels of) ampicillin or tetracycline. By using plasmids containing antibiotic resistance genes, the researcher can kill off all the bacteria which have not taken up his plasmid, thus ensuring that the plasmid will be propagated as the surviving cells divide.


An immunological protein which binds to a specific antigen (ligand); Inducible immunoglobulin proteins produced by the B lymphocyte cells of the immune system of the body in response to an antigen.
Recognizes and binds to a specific antigen molecule of a foreign substance introduced into the organism, such as bacteria, viruses, molds, infections, and pollen (which causes hay fever and other allergic reactions)
When antibodies bind to corresponding antigens they set in motion a process to eliminate the antigens.

Antibody-mediated immunity  

Immune reaction that protects primarily against invading viruses and bacteria through antibodies produced by plasma cells.
It is also known as humoral immunity.


A sequence o f three nucleotides on the transfer RNA (tRNA) molecule that recognizes and pairs with a specific complememntary codon on a messenger RNA molecule.
A nucleotide triplet in a tRNA molecule that aligns with a particular codon in mRNA under the influence of the ribosome, so that the amino acid carried by the tRNA is added to a growing protein chain.
An anticodon helps control the sequence of amino acids in a growing polypeptide chain.


A group of medications which are prescribed to control seizures (e.g., Dilantin, Phenobarbital, Mysoline, Tegretol).
There are many different types of anti-convulsant, and most work by preventing the abnormal electrical outbursts in the brain which lead to the seizure.


Medication used to treat depression.


The antiderivative of a function, f(x), is a function, F(x), whose derivative is f(x).   
Also called the indefinite integral.

Antidiuretic hormone (ADH)

Hypothalamic hormone secreted by the posterior pituitary gland.
It regulates the amount of water excreted by the kidneys.


A ligand that contains a region or epitope which is specifically recognized by an antibody binding site; Any of a class of biochemical substances that stimulate the immune system to produce antibodies.

Antigen binding site

Specialized ends of antibodies that bind specific antigens.

Antigenic determinant 

The site on an antigen to which an antibody binds, forming an antigen-antibody complex.

Antigenic switching

The altering of a microorganism's surface antigens through genetic rearrangement, to escape detection by the host's immune system.

Antiglobulin test

A laboratory test to identify antibodies that can bind to the surface of red blood cells or platelets and destroy them.
This test is used to diagnose certain blood disorders in which patients make antibodies to their own red blood cells or platelets. It is also used to determine blood type.


A hardware construct that uses weight bearing to provide dynamic compression of a fracture. It is usually employed for oblique fractures of the fibula. A plate with screws is affixed to the proximal fibula such that the tip of the distal fracture fragment is wedged between the plate and the proximal fragment. It is not necessary to place screws in the plate distal to the fracture, although an "anti-glide" screw can be placed at the apex of the fracture.


Drugs which antagonize (or counteract) the action of histamine.
Used in the treatment of certain allergic conditions such as hay fever, nettlerash and certain forms of eczema

Anti-inflammatory Agent

(non-steroidal)Anti-inflammatory agents that are not steroids.They have painkiller and fever reducing actions.

(steroidal)Agents capable of suppressing or counteracting the inflammatory process by acting on body mechanisms. They are used primarily in the treatment of chronic arthritic conditions and certain soft tissue disorders associated with pain and inflammation.


A chemical agent that kills microorganisms or inhibits their growth.


A mutant expressing some agent that antagonizes a normal gene product.

Antinuclear antibodies

Antibodies that attack cell nuclei.
Associated with systemic autoimmune diseases involving connective tissue disorders such as systemic lupus erythematosus, Sjögren’s syndrome, etc.


1. A substance that protects cells from damage caused by free radicals (unstable molecules made by the process of oxidation during normal metabolism).
2. A molecule that protects cells from oxidative damage of oxygen and free radical molecules that are chemically unstable and cause random reactions damaging proteins, nucleic acids, and cell membranes. Chemicals approved for the control of oxidation (rancidity) in food products.
1. Free radicals may play a part in cancer, heart disease, stroke, and other diseases of aging. Antioxidants include beta-carotene, lycopene, vitamins A, C, and E, and other natural and manufactured substances.
2. Examples of dietary antioxidants are vitamins C, E, and K, and diverse plant products such as lycopene, a nutraceutical found in tomatoes.Approved antioxidants include: BHT, BHA, propyl-gallate. Regulations limit concentration to 0.003% for individual chemicals, 0.006% for combinations.


A term used to describe the opposite orientations of the two strands of a DNA double helix; the 5' end of one strand aligns with the 3' end of the other strand.


A mechanism for transporting two small molecules and/or ions in opposite directions.
In antiport systems the transported molecules/ions are moved in opposite directions across a cell membrane (see Symport)

Antiretroviral agents

An agent that inhibits the activity of a retrovirus.
A retrovirus is a particular virus characterized by a reversing of the transfer of genetic code information from one type to another.

Anti-Rh gamma globulin (RhoGAM)

A medication used to combat incompatibility in blood type between a mother and her fetus.


Blood serum which contains antibodies.

Antisense DNA or RNA

A DNA or RNA sequence that is complementary to mRNA and can hybridise with it.
They may be used to block the production of proteins needed for cell growth.
Antisense DNA: Small pieces of DNA that can bind to specific molecules of RNA and block the cell’s ability to use the RNA to make a protein.
Antisense RNA: Small pieces of RNA that can bind to specific molecules of RNA and block the cell’s ability to use the RNA to make a protein.

Anti-sense technology

The use of an RNA molecule to block gene expression by interfering with protein production.

Antisocial personality disorder

A lack of socialization along with behaviour patterns that bring a person repeatedly into conflict with society.
The behaviours include incapacity for significant loyalty to others or to social values, callousness, irresponsibility, impulsiveness and an inability to feel guilt or learn from experience or punishment Frustration tolerance is low and such people tend to blame others or give plausible rationalizations for their behavior. Characteristic behavior appears before age 15, although the diagnosis may not be apparent until adulthood.

Antiterminator protein A

Protein that, when bound at its normal attachment sites in DNA, lets RNA polymerase read through normal terminator sequences (eg the N- and Q- gene products of phage lambda).

Anxiety disorders

Conditions that are characterized by excessive fears or anxieties about persons, places, or events.
Persons with anxiety disorders display exaggerated or inappropriate responses to the perception of internal or external dangers.


A category of behavior disorder.
Involves over-anxiety, social withdrawal, seclusiveness, shyness, sensitivity, and other behaviors implying a retreat from the environment.


Arbeitsgemeinschaft fur Osteosynthesfragen/Association for the Study of Internal Fixation. An association founded in Germany to study and promote the use of internal fracture fixation. The association has an education program for teaching surgical methods. There are national branches of the association in several countries. In the United States, it is the Association for the Study of Internal Fixation. Several types of orthopedic hardware have been developed by AO, and they are given AO designations, e.g. an AO screw.


The major artery that conveys blood from the heart to the major organs


Pertaining to the aorta , the largest artery in the body.

Aortic valve

One of the four valves in the heart, this valve is situated at exit of the left ventricle of the heart where the aorta (the largest of all arteries) begins.


Inflammation of the aorta . The causes of aortitis include syphilis or rheumatic fever .

Aortocoronary bypass (or coronary artery bypass, CAB)

Surgery in which a healthy blood vessel taken from another part of the body is used to make a new path for blood around a blocked artery to the heart.
This restores the flow of oxygen and nutrients to the heart.


A transcription factor that enhances the production of inflammatory mediators.
Association of this transcription factor with the GR complex results in decreased transcription of COX-2 genes.
AP-1 site = The binding site on DNA at which the transcription "factor" AP-1 binds, thereby altering the rate of transcription for the adjacent gene. AP-1 is actually a complex between c-fos protein and c-jun protein, or sometimes is just c-jun dimers. The AP-1 site consensus sequence is (C/G)TGACT(C/A)A. Also known as the TPA-response element (TRE). [TPA is a phorbol ester, tetradecanoyl phorbol acetate, which is a chemical tumor promoter]

AP endonuclease

Endonuclease that initiates excision repair at apurinic and apyrimidinic sites on DNA.


Refers to the lack of symmetry in molecular structures or functions.
An important insight into the mechanism of biological structures is their aperiodic composition and distribution of atoms causing the extraordinary complexity of cells.


Small opening

APGAR score

An evaluation of a newborn's physical condition after birth that enables quick identification of the infant at risk.
It is the sum of ratings (0, 1, & 2) on five criteria; appearance or coloring, pulse (heart rate), grimace (responsiveness to stimuli), activity (muscle tone), and respiration. (The first letter in each word combines to make the acronym APGAR.) Ratings are taken at one minute and again at five minutes after birth.


Loss of speech: Loss of the ability to express oneself and/or to understand language.
An acquired language disorder in which there is a loss of speech and language ability resulting from a stroke, disease, or head injury. This loss of impairment results in the ability to use words to understand language symbols in reading, writing, or speaking. Several classifications are used, including expressive and receptive, congenital, developmental, and acquired aphasia.


A procedure in which blood is collected, part of the blood such as platelets or white blood cells is taken out, and the rest of the blood is returned to the donor.


Relating to the apex, the anterior pole.


A period of time during which breathing stops or is markedly reduced.
There are two types of apneas, the more common obstructive sleep apnea and the less common central sleep apnea. Apneas usually occur during sleep, and when they do occur, sleep is usually disrupted. Sometimes the person wakes up completely, but sometimes the person comes out of a deep level of sleep and into a more shallow level of sleep. Apneas are usually measured during sleep (preferably in all stages of sleep). An estimate of the severity of apnea is calculated by dividing the number of apneas by the number of hours of sleep, giving an apnea index (AI). The greater the apnea index, the more severe the apnea.   (see Sleep apnea)

Apocrine glands

Sweat glands that are located primarily in the armpits and groin area; larger than the more widely distributed eccrine glands.


The inactive protein portion of an enzyme that requires the attachment of a cofactor to form an active enzyme.

Apolipoprotein E

A protein whose main function is to transport cholesterol.
The gene for this protein is located on chromosome 19 and is referred to as APOE. There are three forms of APO: ε2, ε3, and ε4. The latter form is associated with about 60% of late-onset Alzheimer’s disease cases and is considered to be a risk factor for the disease.

Apomorphic character

A derived phenotypic character, or homology, that evolved after a branch diverged from a phylogenetic tree;
A character state derived by evolution from an ancestral state (plesiomorphy). A novel evolutionary trait.
See Autapomorphy


Collagenous sheets or ribbons that resemble flat, broad tendons.
May cover the surface of a muscle and assist in attaching superficial muscles to another muscle or structure.


Programmed cell death, the body's normal method of ending the life cycle of cells through cellular self destruction.
It is brought about by signals that trigger the activation of a cascade of "suicide" proteins in the cells destined to die.

Failure of apoptosis is one of the main contributions to tumour development and autoimmune diseases: when either heritable or somatic cell mutations cause malfunctions to occur in the apoptotic pathway, uncontrolled cell growth may proceed unchecked and cancer may result.


The perpendicular distance from the center to a side of a regular polygon.

Appropriation doctrine

The system for allocating water to private individuals used in most Western states. The doctrine of Prior Appropriation was in common use throughout the arid west as early settlers and miners began to develop the land. The prior appropriation doctrine is based on the concept of "First in Time, First in Right." The first person to take a quantity of water and put it to Beneficial Use has a higher priority of right than a subsequent user. Under drought conditions, higher priority users are satisfied before junior users receive water. Appropriative rights can be lost through nonuse; they can also be sold or transferred apart from the land. Contrasts with Riparian Water Rights.

Appetitive behaviours

Behaviours that establish, maintain, or promote sexual interaction.
Females engaging in such behaviours are said to be proceptive and proceptive behaviours often include movements, postures, and vocalizations. Male appetitive behaviour is most often maintaining proximity


Inability to carry out motor acts on command in the absence of paralysis.
Not due to paralysis, sensory changes, or deficiencies in understanding.


A condition in which there is a loss of production or comprehension of the meaning of different tones of voice.

A protein

A protein found in the cell wall of the bacterium Staphylococcus aureus which binds to the Fc section of immunoglobulins and is therefore used to collect antigen-antibody complexes.


Farming of plants and animals that live in water, such as fish, shellfish, and algae.


A pipe, conduit, or channel designed to transport water from a remote source, usually by gravity.


A geologic formation(s) that is water bearing. A geological formation or structure that stores and/or transmits water, such as to wells and springs. Use of the term is usually restricted to those water-bearing formations capable of yielding water in sufficient quantity to constitute a usable supply for people's uses.


Soil or rock below the land surface that is saturated with water. There are layers of impermeable material both above and below it and it is under pressure so that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer.

Aquifer (unconfined)

An aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall.


A transport protein in the plasma membranes of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis).
It forms a pore / channel that allows for much faster movement of water from one side to the other of the cell membrane.

Aqueous humor

In the eye, a nutritive, watery fluid between the cornea and the lens that focuses incoming light rays and maintains the shape of the eyeball.


prokaryotic form of life that forms a domain in the tree of life.
There are three domains: bacteria, archaea, and eukarya. Bacteria are also prokaryotic organisms. Eukaryotes include animals, plants, fungi, and protozoan and have very different cell structures, bigger and with internal membrane bound structures (organelles). While bacteria and archaea look similar in structure, they have very different metabolic and genetic activity. One defining physiological characteristic of archaea is their ability to live in extreme environments. They are often called extremophiles and unlike bacteria and eukarya depend on either high salt, high or low temperature, high pressure, or high or low pH.

Arachidonic acid

An omega-6 fatty acid.
It is the compound from which inflammatory mediators such as leukotrienes, thromboxanes, and prostaglandins are produced.

Arachnoid mater

The middle of the three connective tissue membranes (the meninges) that cover and protect the brain and spinal cord. Arachnid means spider, and the name comes from fine threads of arachnoid tissue spreading across the subarachnoid space.
A thin transparent avascular membrane with trabeculae that communicate with the pia mater and in places pierces the dura mater to form arachnoid villi projecting into the dural sinuses.  The villi are important in absorption of cerebrospinal fluid as they transport the CSF from the subarachnoid space to the dural sinuses.

There are two cavities bordering the arachnoid:
The subdural space occurs between the arachnoid and the dura mater, the outermost menynx (singular formeninges).
The subarachnoid space lies inside the arachnoid. This space contains blood vessels and circulates CSF. The fine threads of tissue that spread across this space resemble the web of a spider and give the arachnoid layer its name.
(see Dura Mater, MeningesPia Mater)


Organisms living on or in trees, fequenting trees, or a part of an organism resembling a tree in form and branching structure.


The set of points on a circle that lie in the interior of a central angle.


The inverse of various trigonometric functions.
arc length:  s = integral (sqrt (1 + (dy/dx)2)) dx.

arccos:  If x = cos y, then y = arccos x.  The inverse of the cosine function.

arccsc:  If x = csc y, then y = arccsc x.  The inverse of the cosecant function.

arccot:  If x = cot y, then y = arccot x.  The inverse of the cotangent function.

arcsec:  If x = sec y, then y = arcsec x.  The inverse of the secant function.

arcsin:   If x = sin y, then y = arcsin x.  The inverse of the sine function.

arctan:   If x = tan y, then y = arctan x.  The inverse of the tangent function.


Endoderm-lined cavity formed during gastrulation by invagination of the vegetal plate cells (in sea urchin) or involution of cells at the blastoporal lip (in amphibians);.
It will become the interior of the primitive gut.

Arginine Clonidine Growth Hormone Stimulation Tests

A laboratory test used to diagnose growth hormone deficiency.


The independent variable in a function.

Arithmetic sequence

A sequence of numbers of the form  a, a + b, a + 2b, a + 3b, ... , a + (n - 1)b

Arithmetic series

The sum of an arithmetic sequence.

Arm fat area

Calculation based on arm muscle circumference and upper arm area.
An indice of an individual's fat stores.

Arm muscle area

Calculation based on upper arm area and arm muscle area.
An indice of an individual's muscle stores.

Arm span

A measurement of the distance between the middle fingertips of the left and the right hands when arms are spread out as far as possible used to help identify growth disorders.


Being awake. Primitive state of alertness managed by the reticular activating system (extending from medulla to the thalamus in the core of the brain stem) activating the cortex.
Cognition is not possible without some degree of arousal.

Arrayed library

Individual primary recombinant clones (hosted in phage, cosmid, YAC, or other vector) that are placed in two-dimensional arrays in microtiter dishes.
Each primary clone can be identified by the identity of the plate and the clone location (row and column) on that plate. Arrayed libraries of clones can be used for many applications, including screening for a specific gene or genomic region of interest as well as for physical mapping.
Information gathered on individual clones from physical map analyses is entered into a relational database and used to construct physical and genetic linkage maps simultaneously; clone identifiers serve to interrelate the multilevel maps.

Arrhenius acid

A substance which ionizes in aqueous solution to yield hydrogen ions (H+).
Lewis acid: a substance which acts as an electron pair donor.
Bronsted-Lowry acid: a substance which acts as a proton (H+) donor.
Arrhenius base: a substance which ionizes in aqueous solution to yield hydroxide ions (OH-)
Lewis base: a substance which acts as an electron pair acceptor.
Bronsted-Lowry base: a substance which acts as a proton (H+) acceptor.


Pertaining to the blood vessels that convey blood from the heart to other tissues.

Arterial embolization

The blocking of an artery by a clot of foreign material.
This can be done as treatment to block the flow of blood to a tumor.

Arteriographic examination

A visual examination of an artery or arteries, after injection of dyes and other matter that can be seen by x-rays.
Arteriogram: X-ray visualization of the arterial lining after injection of radiopaque dye into a specific artery or into the bloodstream.
It aids in the diagnosis of vascular occlusions and of athrosclerotic plaques, as well as of other cardiovascular abnormalities.


A cardiovascular disease caused by the formation of hard plaques within the arteries.

Artesian water

Ground water that is under pressure when tapped by a well and is able to rise above the level at which it is first encountered. It may or may not flow out at ground level. The pressure in such an aquifer commonly is called artesian pressure, and the formation containing artesian water is an artesian aquifer or confined aquifer. See flowing well


Pain in a joint.


A disease involving inflammation of the joints due to infections, metabolic, or genetic causes.
Joint injury can be caused by trauma or by the wear and tear of aging. The general term arthritis includes over 100 kinds of diseases, most of which last for life. In many forms of arthritis, injury is caused by the uncontrolled inflammation of autoimmune disease, in which the immune system attacks the body's own tissues. Common kinds of arthritis include osteoarthritis and rheumatoid arthritis.


A sterile needle and syringe are used to drain joint fluid out of the joint for study in the laboratory.


A procedure where by a needle in introduced into a joint space for the purpose of removing joint fluid. This procedure can also be therapeutic if an anesthetic or corticosteroid medication is injected into the joint during the procedure.


Any disease that affects joints.


A technique using a fibre optic instrument to visualize surfaces of bones entering into a joint, find tears in internal joint structures. Used to evaluate sources of inflammation in a joint cavity.

Arthroscopic Knee Repair

A fiber optic procedure, used in the surgical repair of any of several knee ligaments including the anterior cruciate ligament (ACL) or of the knee cartilages (meniscus). See Encyclopedia


A surgical incision into a joint.


An operation that restore as far as possible the integrity and function of a joint. In general, an arthroplasty involves prosthetic replacement of one or both sides of a joint. A hemiarthroplasty involves replacement of only one side of a joint. A total joint arthroplasty involves replacement of both sides of a joint. A hemiarthroplasty may be unipolar of bipolar.


Movement of the lips, tongue, teeth and palate into specific patterns for purposes of speech; The ability to make specific sounds: i.e., the "g" in gum, the "b" in bear, the "s" in snake.
Also, a movable joint.
Articulation is the component most often affected in children with speech disorders of unknown cause.
articulation disabilities: Speech problems such as omissions, substitutions, additions, and distortions.
articulation disorders: Difficulties with the way sounds are formed and strung together, usually characterized by substituting one sound for another (wabbit for rabbit), omitting a sound (han for hand), or distorting a sound (shlip for sip).
articulation errors: A speech problem seen in children, which may take one of the following forms: distortions, omissions, substitutions, and/or additions.

Artificial recharge

An process where water is put back into ground-water storage from surface-water supplies such as irrigation, or induced infiltration from streams or wells.

Artificial insemination

A breeding technique, most commonly used in domestic animals and sometimes in captive breeding of wild animals, in which semen is introduced into the female reproductive tract by artificial means


Any number of the six naturally occurring minerals, that readily separate into long, flexible fibres, traditionally used for insulation in industry, construction, and textile manufacturing,
The fibre was formerly widely used in brake linings, gaskets, and insulation; and in roofing shingles, floor and ceiling tiles, cement pipes, and other building materials. Asbestos fabrics were used for safety apparel and for such items as theatre curtains and fire stop hangings in public buildings.


A non-cancerous condition caused by asbestos exposure those results in severe fibrosis and destruction of lung tissue.

ASCII (American Standard Code for Information Interchange)

A character encoding scheme used by many computers.
The ASCII standard uses 7 of the 8 bitsbyte to define the codes for 128 characters. E.g., in ASCII, the number seven is a treated as a character and is encoded as: 00010111. Because a byte can have a total of 256 possible values, there are an additional 128 possible characters that can be encoded into a byte, but there is no formal ASCII standard for those additional 128 characters. Most IBM compatible personal computers do use an IBM "extended" character set that includes international characters, line and box drawing characters, Greek letters, and mathematical symbols.

Ascorbic acid or Ascorbate

Chemical name for vitamin C.
Lemon juice contains large quantities of ascorbic acid and is commonly used to prevent browning of peeled, light-coloured fruits and vegetables. Green peppers, broccoli, citrus fruits, tomatoes, strawberries, and other fresh fruits and vegetables are good sources of vitamin C.


Suffix used for the name of an enzyme.
Examples: polymerase, lipase, cellulase.


Describing a procedure that is conducted under sterile conditions.

Aseptic necrosis

Condition in which poor blood supply to an area of bone leads to bone death. Also called avascular necrosis and osteonecrosis

Asexual reproduction

Reproduction of a plant or animal without fusion of male and female gametes; A type of reproduction involving only one parent that usually produces genetically identical offspring.
Asexual reproduction occurs without meiosis or syngamy, and may happen though budding, by the division of a single cell, or the breakup of an entire organism into two or more parts. The reproduction involves only one parent and produces genetically identical offspring by budding or by the division of a single cell or the entire organism into two or more parts.
Includes vegetative propagation, cell and tissue culture.


A low-calorie sweetener used in a variety of foods and beverages and as a tabletop sweetener.
It is about 200 times sweeter than sugar. Aspartame is made by joining two protein components, aspartic acid and phenylalanine.


An impaired or absent exchange of oxygen and carbon dioxide.


A chemical (gas or vapor) that can cause death or unconsciousness by suffocation.


The entrance (through inhaling) of material (e.g., food, saliva) into the trachea or airway below the level of the true vocal cords.
Can cause a lung infection or pneumonia.

Aspiration pneumonia

A lung inflammation caused by inhaling a foreign body, such as food, into the lungs.

Aspirin or Acetylsalicylic acid

A compound that is part of a group of drugs called salicylates.
Aspirin is widely used for relieving pain and reducing fever in adults. It also relieves mild itching and reduces swelling and inflammation. Use of aspirin by children has been linked to the occurrence of a disorder known as Reye’s Syndrome.


A method for determining the presence or quantity or activity or concentration of a chemical.

Assay box

A selection box listing all of the assay runs and nonimmunoassay batches currently defined and awaiting computation or printing.
It is used to select an assay run to review, modify, or delete. Once a new assay run has been successfully computed and saved in the test data file, the assay run is deleted from the assay box.

Assay data file

Temporary files which contain all of the data necessary to compute a new assay run.
All assay runs listed in the Assay Table (accessed from the main screen) or the assay box in Assay Run Setup (Modify) have corresponding assay data files. When a new assay run has been successfully computed and saved in the test data file, the assay data file is deleted.

Assay information table

An assay information table is a set of reference or current assays which contains fifteen items of information specific for each assay run.

Assay run

A set of standard samples, control samples, and unknown samples which are analyzed and computed together in a single batch.

Assay set

A group of assay runs comprising all of the reference assays (maximum 30 assay runs) or all of the current assays (maximum 30 assay runs).

Assay set table

A listing of all thirty reference assay runs and all thirty currrent assay runs.
The assay runs are identified by assay name and assay date.

Assay table

A table listing pertinent information about the newly defined assay runs awaiting computation.
Once a new assay run has been successfully computed and saved in the test data file, the assay run is deleted from the assay table. Some of the information in this table can be modified and the sequence of assay runs can also be changed.

Assay Worklist Report

A listing of the placement of the baseline standard samples, standard samples, control samples, and unknown samples.
The assay worklist report also includes unknown record information and other information relating to a specific assay run.

Assignment test

A test that determines whether a locus is on a specific human chromosome by observation of the concordance of the locus and the specific chromosome in a panel of human-mouse hybrid cell lines containing only one or a few of the normal set (22 autosomes, X and Y) of human chromosomes.

Associative or Association learning

The acquired ability to associate one stimulus with another; The principle that items experienced together enter into a connection, so that one tends to reinstate the other.
Also called classical conditioning.

Associative property of addition

(a + b) + c = a + (b + c)

Associative property of multiplication

(a * b) * c = a * (b * c)

Assortative mating

The mating of individuals with similar phenotypes.


Inability to recognize things by touch.


Clinical sign or symptom manifested as debility, or lack or loss of strength and energy.


Term generally used to describe complaints related to refractive error, ocular muscle imbalance, including pain or aching around the eyes, burning and itchiness of the eyelids, ocular fatigue, and headaches.


A chronic inflammatory lung disorder characterized by obstruction of airways.
A form of bronchial disorder associated with airway obstruction, marked by recurrent attacks of paroxysmal dyspnea, with wheezing due to spasmodic contraction of the bronchi.


A refractive problem that reduces the quality of vision, arising from unequal curvature of the refractive surfaces of the eye.

A point source of light cannot be brought to a point focus on the retina but is spread over a more or less diffuse area. This results from the radius of curvature in one plane being longer or shorter than the radius at right angles to it and occurs when the surface of the cornea is uneven or structurally defective, preventing the light rays from converging at a point.


Ability of substances to cause the surface of the mouth cavity to contract.


A class of large neuroglial (macroglial) cells in the central nervous system - the largest and most numerous neuroglial cells in the brain and spinal cord.
Astrocytes (from "star" cells) are irregularly shaped with many long processes, including those with "end feet" which form the glial (limiting) membrane and directly and indirectly contribute to the blood brain barrier. They have a number of important homeostatic and structural functions including regulating the extracellular ionic and chemical environment, and "reactive astrocytes" (along with microglia) respond to injury.


Neoplasms of the brain and spinal cord derived from glial cells which vary from histologically benign forms to highly anaplastic and malignant tumors.
Fibrillary astrocytomas are the most common type and may be classified in order of increasing malignancy (grades I through IV). In the first two decades of life, astrocytomas tend to originate in the cerebellar hemispheres; in adults, they most frequently arise in the cerebrum and frequently undergo malignant transformation.

Also known as Anaplastic Astrocytoma; Astrocytoma, Grade I; Astrocytoma, Grade II; Astrocytoma, Grade III; Astrocytoma, Protoplasmic; Astroglioma; Cerebral Astrocytoma; Childhood Cerebral Astrocytoma; Fibrillary Astrocytoma; Gemistocytic Astrocytoma.


A family of RNA viruses with one genus: ASTROVIRUS.
They cause gastroenteritis in humans and also infect other vertebrates.


A genus of small, circular RNA viruses in the family Astroviridae.
They cause gastroenteritis and are found in the stools of several vertebrates including human infants, calves, lambs, and piglets. Transmission is by the fecal-oral route. There are at least eight human serotypes and the type species is Human astrovirus 1.

Asymmetrical standard curve

A sigmoidal curve with one asymptote more elongated than the other asymptote when the response of each standard is plotted against the logarithm of its respective concentration.

Asymmetrical tonic neck reflex (ATNR)

Primitive reflex exhibited by stimulation of proprietors in the neck joint.
Arm and leg on same side as the back of the head remain partially flexed, while the arm and leg on the fore side extend almost fully.


The two ends of a sigmoid curve which plateau on the response axis as the curve approaches infinitely high and infinitely low x values.
A straight line that is a close approximation to a curve as the curve goes off to infinity.


A genus of adenoviridae that comprises viruses of several species of mammals and birds.
The type species is Ovine adenovirus D.


Impairment of the ability to perform smoothly coordinated voluntary movements; awkwardness and lack of fluidity in motor behaviour (extreme difficulties in controlling fine and gross motor movements and balance).
A problem of muscle coordination not due to apraxia, weakness, rigidity, spasticity or sensory loss. This condition may affect the limbs, trunk, eyes, pharynx, larynx, and other structures. Can interfere with a person's ability to walk, talk, eat, and to perform other self care tasks.
Generally associated with loss of control mechanisms resulting from damage to the cerebellum or basal ganglia, but ataxia may result from impaired sensory or motor function.
Sensory ataxia may result from posterior column injury or peripheral nerve diseases. Motor ataxia may be associated with cerebellar diseases, cerebral cortex diseases, thalamic diseases, basal ganglia diseases, injury to the red nucleus and other conditions.
ataxic syndrome: Imbalance and lack of coordination of voluntary movement


A disease (loss of muscle control, and reddening of the skin) in human beings caused by a defect in DNA repair mechanisms.
An autosomal recessive inherited disorder characterized by choreoathetosis beginning in childhood, progressive cerebellar ataxia, telangiectasis of conjunctiva and skin, dysarthria, B- and T-cell immunodeficiency, and radiosensitivity to ionizing radiations (X-rays, beta and alpha particles, gamma rays). Affected individuals are prone to recurrent sinobronchopulmonary infections, lymphoreticular neoplasms, and other malignancies. Serum Alpha-fetoproteins are usually elevated. The gene for this disorder (ATM) encodes a cell cycle checkpoint protein kinase and has been mapped to chromosome 11 (11q22-q23).


Collapse of the lung.
Collapsed or airless state of the lung, which may be acute or chronic and affect all or part of a lung. May be caused by obstruction

(A+T)/(G+C) ratio

A reference to the base composition of double-stranded DNA.
DNA from different sources has different ratios of the A-to-T and G-to-C base pairs, e.g. DNAs isolated from organisms that live in hot springs have a higher GC content, which takes advantage of the increased thermal stability of the GC base pair.


The codon for methionine; the translation initiation codon.
Usually, protein translation can only start at a methionine codon (although this codon may be found elsewhere within the protein sequence as well). In eukaryotic DNA, the sequence is ATG; in RNA it is AUG. Usually, the first AUG in the mRNA is the point at which translation starts, and an open reading frame follows - i.e. the nucleotides taken three at a time will code for the amino acids of the protein, and a stop codon will be found only when the protein coding region is complete.

Atherectomy, Coronary

Percutaneous transluminal procedure for removing atheromatous plaque from the coronary arteries.
Both directional (for removing focal atheromas) and rotational (for removing concentric atheromatous plaque) atherectomy devices have been used.


Literally, "hardening of the fatty stuff". Formation of fatty plaques lining blood vessels.
The fatty areas can become calcified and hard, leading to arteriosclerosis - hardening of the walls of the medium and large muscular arteries - due to thickening and loss of elasticity, with lesions in the innermost layer of the artery (Arterial intima).

When blood vessels become less stretchable, blood pressure rises and can result in heart and kidney damage and strokes.

This disease process of atherogenesis includes the retention of cholesterol-rich lipoproteins and their binding to proteoglycans in the arterial intima, generation of proinflammatory molecules that recruit macrophages to the subendothelial space, formation of foam cells, and eventual calcification of the arterial wall. These arterial plaques (atheromas) contain carbohydrates, blood and calcium.


1. A condition characterized by constant, contorted twisting motions in the
wrists and fingers. 2. Slow, smooth movements; mostly involving muscles of the arms and legs.
Also known as Hammond’s disease.
A dyskinesia characterized by an inability to maintain the fingers, toes, tongue, or other body parts in a stable position, resulting in continuous slow, sinusoidal, and flowing involuntary movements. This condition is frequently accompanied by chorea, where it is referred to as choreoathetosis. Athetosis may occur as a manifestation of basal ganglia diseases or drug toxicity.

AT Hook Motifs

DNA-binding motifs, first described in one of the HMGA proteins specifically HMG-I(Y) protein.
They consist of positively charged sequences of nine amino acids centered on the invariant tripeptide glycine-arginine-proline. They act to fasten the protein to an A-T rich sequence in the DNA.

Atlantoaxial joint

The joint involving the atlas and axis bones.

Atlantoaxial instability

A misalignment of the top two vertebrae of the neck, which is more commonly found in persons with Down Syndrome.
This condition makes these persons more prone to injury if they participate in activities which overextend or flex the neck. Proper diagnosis can help prevent serious injury.

Atmospheric Pressure

A force over a given area that is caused by the weight of an atmosphere.


The blanket of air that surrounds the Earth.  It is thickest near the ground and gradually fades away to nothing in outerspace.


The smallest unit of matter as recognized by chemical properties of molecules; The smallest part of a substance that can take part in a chemical reaction.Composite particles of protons, neutrons and electrons. The latter provide all properties described by molecular interactions and chemical reactions that are essential processes in biology. made up of protons and neutrons in a central nucleus surrounded by electrons.  The smallest particle of a chemical element that can take part in a chemical reaction without being permanently changed.

Atomic Absorption Spectrophotometry / Spectroscopy (AAS)

A quantitative, analytical technique used for determining the presence, and to measure  concentration, of a wide range of elements in materials such as metals, pottery and glass, in liquid samples.
A very small sample size (typically about 10 milligrams) is accurately weighed and then dissolved, often using strong acids. The resulting solution is sprayed into the flame of the instrument and atomised. Light of a suitable wavelength for a particular element is shone through the flame, and some of this light is absorbed by the atoms of the sample. The amount of light absorbed is proportional to the concentration of the element in the solution, and hence in the original object. Measurements are made separately for each element of interest in turn to achieve a complete analysis of an object, and thus the technique is relatively slow to use. However, it is very sensitive and it can measure trace elements down to the part per million level, as well as being able to measure elements present in minor and major amounts.

Although a destructive technique, the sample size needed is very small and its removal causes little damage.
(see Inductively Coupled Plasma Mass Spectrometry)

Atomic mass unit (amu)

1/12 the mass of a carbon-12 atom.

Atomic number

The number of protons in the nucleus of an atom.
Unique for each element and designated by a subscript to the left of the elemental symbol

Atomic symbol

The letters representing each of the elements.

Atomic weight

The average weight of an atom.


A condition evidenced by lack of muscle tone.


Loss of ability to correctly locate a sensation.


See Adenosine triphosphate

ATP Binding Cassette Transporters

A family of membrane transport proteins that require ATP hydrolysis for the transport of substrates across membranes.
The protein family derives its name from the ATP-binding domain found on the protein.
See ABC proteins.

ATPCitrate (pro-S)-Lyase

An enzyme that, in the presence of ATP and COENZYME A, catalyzes the cleavage of citrate to yield acetyl CoA, oxaloacetate, ADP, and Orthophosphate.
This reaction represents an important step in fatty acid biosynthesis. This enzyme was formerly listed as EC

ATP-Dependent Proteases

Proteases that contain proteolytic core domains and ATPase-containing regulatory domains.
They are usually comprised of large multi-subunit assemblies. The domains can occur within a single peptide chain or on distinct subunits.

ATP synthase

A cluster of several membrane proteins found in the mitochondrial cristae (and bacterial plasma membrane) that function in chemiosmosis with adjacent electron transport chains, using the energy of a hydrogen-ion concentration gradient to make ATP.
ATP synthases provide a port through which hydrogen ions diffuse into the matrix of a mitrochondrion.

ATP Synthetase Complexes

Multisubunit enzyme complexes that synthesize Adenosine Triphosphate from energy sources such as ions traveling through channels.


Absence of a normal body opening, such as atresia of the ear canal.

Atrial Appendage

Ear-shaped appendage of either atrium of the heart.

Atrial fibrillation

Disorder of cardiac rhythm characterized by rapid, irregular atrial impulses and ineffective atrial contractions: the most common cardiac arrhythmia.
The hallmarks of AF are irregular and rapid atrial activity, with an irregular ventricular response that results in compromised cardiac hemodynamics. AF is associated with serious morbidity and increased mortality risk, even in cases when symptoms are slight. AF is a risk for congestive heart failure (CHF), angina, cardiac remodeling, and embolic stroke.

Atrial flutter

Rapid, irregular atrial contractions due to an abnormality of atrial excitation.

Atrial Myosins

Atrial Myosin type II isoforms specifically found in the atrial muscle of the heart.

Atrial Natriuretic Factor

A potent natriuretic and vasodilatory peptide or mixture of different-sized low molecular weight peptides derived from a common precursor and secreted mainly by the heart’s atrium.
All these peptides share a sequence of about 20 amino acids.
The peptides include: ANF (1-126); ANF (1-28); ANF (99-126); ANF Precursors; ANP (1-126); ANP (1-28); ANP Prohormone (99-126); ANP-(99-126); Atrial Natriuretic Factor (1-126); Atrial Natriuretic Factor (1-28); Atrial Natriuretic Factor (99-126).

Atrial Premature Complexes

Premature contractions of the heart arising from an ectopic atrial focus.
With ventricular premature complexes, they represent one of the most common causes of irregular pulse. They are more apt to occur if there is atrial or conduction system disease such as left atrial enlargement in mitral stenosis. In community prospective studies, atrial premature complexes are not related to sudden death, as are ventricular premature beats in coronary disease.

Atrioventricular node

A small nodular mass of specialized muscle fibers located in the interatrial septum near the opening of the coronary sinus. It gives rise to the atrioventricular bundle of the conduction system of the heart.
A group of slow-conducting fibers in the atrium of the vertebrate heart that are stimulated by impulses originating in the sinoatrial node (the pacemaker) and that conduct impulses to the bundle of His, a group of fibers that stimulate contraction of the ventricles.

Atrioventricular valve

A valve in the heart between each atrium and ventricle that prevents a backflow of blood when the ventricles contract.


A wasting away or decrease in size of a cell, tissue, organ, or part of the body caused by lack of nourishment, inactivity or loss of nerve supply; Muscle degeneration resulting from lack of use or immobilization.

Attached X

A pair of Drosophila X chromosomes joined at one end and inherited as a single unit.


The attachment of muscle (by means of a tendon) to the bone.
Formerly described as Origin and Insertion, depending on which end of the muscle was being described. These terms have been replaced by Attachment.

Attachment site (microbiological)

Specific loci on both the bacterial DNA (attB) and the phage DNA (attP) which delineate the sites where recombination takes place between them, as the phage DNA becomes integrated (inserted) into the bacterial DNA during lysogeny
Also known as Att Attachment Sites; AttB Attachment Sites; AttP Attachment Sites; Attachment Site (Microbiology); Attachment Site, Bacterial; Attachment Sites, Bacterial; Bacterial Attachment Site; Microbiologic Attachment Site; Microbiologic Attachment Sites


The ability to focus on a given task or set of stimuli for an appropriate period of time.

Attention Deficit Disorder (ADD)

A condition characterized by when a person is easily distracted and has difficulty staying focused on an individual activity for any period of time.
ADD affects 3-5% of all students, and is not recognized as a separate category of disability under US federal educational legislation.
See also Attention Deficit Hyperactivity Disorder as these terms are often used interchangeably.

Attention deficit hyperactivity disorder (ADHD)

A behavior disorder originating in childhood in which a child exhibits signs of developmentally inappropriate hyperactivity, impulsivity, and inattention. Although most individuals have symptoms of both inattention and hyperactivity-impulsivity, one or the other pattern may be predominant. These characteristics are usually present before the age of 7. ADHD is similar to "Attention Deficit Disorder", except emphasis is placed on the hyperactivity. Believed to be a condition which affects those parts of the brain which control attention, impulses and concentration.
Argued to affect 3 to 7% of school age children; the disorder is more frequent in males than females.. A  child who suffers from this condition shows disruptive behaviours, which cannot be explained by any other psychiatric condition and are not in keeping with those of the same-aged people with similar intelligence and development.

Children with ADHD have difficulty focussing their attention to complete a specific task. Additionally they can be hyperactive and impulsive and can suffer from mood swings and “social clumsiness”. They are believed to tend to display the following behaviours: -
Impulsive behaviour
Social clumsiness
Poor coordination
Mood swings
Specific learning disabilities such as dyslexia, language problems, difficulties with handwriting / written work.
Children with ADHD are restless and cannot sit still or do any one thing for very long. They are easily distracted and, because they find it so hard to pay attention, they may often be criticised for being careless and making too many mistakes at school. They appear not to listen when someone is talking to them, they find it hard to wait their turn and they can be disruptive in play. In people with ADHD, behavioural problems are seen in several places i.e. not just at school. Some children with ADHD have significant problems with concentration and attention but are not necessarily overactive or impulsive.

These behaviours are usually first noticed in early childhood, and they are more extreme than simple “misbehaving”.

Symptoms often attenuate during late adolescence although a minority experience the full complement of symptoms into mid-adulthood.

Attenuator (in genetics)

A control region at the promoter end of repressible amino acid operons that exerts transcriptional control based on the translation of a small leader peptide gene.
A region adjacent to the structural genes of the trp (tryptophan) operon; in the presence of tryptophan this region acts to reduce the rate of transcription from the structural genes.

Attenuator stem (in genetics)

A configuration of the leader transcript that signals transcription termination in attenuator-controlled amino acid operons.

Atypical Bacterial Forms

Microorganisms that have undergone greater changes than normal in morphology, physiology, or cultural characteristics.


A plot of a person's hearing sensitivity, measured using pure tones, over a range of different frequencies (generally from 250 – 8000 Hz). The audiogram is the auditory equivalent of the Snellen Eye Chart that most of us would have encountered at the optometrist’s for measuring visual acuity.
Usually performed by an audiologist using an instrument called an audiometer.

In the audiogram hearing sensitivity is expressed not as some absolute level but as decibel Hearing Level (dB HL) in which the hearing of the person is measured relative to normal hearing sensitivity (determined previously from a large normative population).  Thus, on the audiometer a value of 0 dB HL represents not some absolute sound pressure level of 0 but rather the sound pressure level corresponding to mean hearing level at that frequency in the normal population.

Audiometers are pre-calibrated so that the value of 0 dB HL at each frequency is equal to the sound pressure level corresponding to mean hearing level at that frequency in the normal population.  Thgus it possible to immediately read off from the audiometer whether a test subject’s hearing is 10, or 20 or 30 etc dB worse than normal hearing sensitivity at a particular test frequency.


One who evaluates hearing defects and who aids in the rehabilitation of those who have such defects.


An electric device used to measure a person's response to sound stimuli.
Usually a pure-tone audiometer is used to generate an audiogram for a subject.

Auditory blending

The act of blending the parts of a word into an integrated whole
when speaking.

Auditory Brainstem Evoked Response (ABER) or ABR or BAER or AEP (auditory evoked potentials)

The electrical responses recorded from auditory brainstem and midbrain structures in response to sound, using electrodes placed over the scalp or forehead, and neck or behind the ears.
(see EEG and ECG for details of other surface recorded electrical responses in the body.)
A very reliable test used to complete an in-depth evaluation of hearing or the auditory system, or when other methods of evaluation have not given reliable results. Most commonly used with infants and other individuals who are hard to test and can be performed while they are sleeping.

Sounds are presented, usually through earphones, and the electrodes pick up the electrical responses of neurons of the auditory nerve and in various lower brain structures in response to the sound. A computer averages the responses and produces an averaged waveform of the brain response.

Careful analysis of the ABER pattern can help identify the presence of certain medical conditions that affect hearing, such as tumors along the auditory pathway or diseases like multiple sclerosis.

Auditory Brain Stem Implant

An electronic device with electrodes surgically inserted to contact the cochlear nucleus in the brain stem rather than to the inner ear as in cochlear implantation.

Auditory closure

The ability of the learner to formulate or recognize a word when one or more parts are not heard (ex: "andy bar" can be heard as candy bar) or when continuity of sound is interrupted by gaps (e.g., c-a-t can be heard as cat).

Auditory discrimination

The ability of the listener to distinguish likenesses and differences between sounds.

Auditory fatigue

Loss of sensitivity to sounds as a result of auditory stimulation, manifesting as a temporary shift in auditory threshold.
The temporary threshold shift, TTS, is expressed in decibels.

Auditory global method

A general term describing an approach to teaching deaf people communication where the main channel for speech and language development is auditory (although not always exclusive) and fluent; connected speech is the means of input.

Auditory perceptual disorders

Acquired or developmental cognitive disorders of auditory perception characterized by a reduced ability to perceive information contained in auditory stimuli despite intact auditory pathways. Affected individuals have difficulty with speech perception, sound localization, and comprehending the meaning of inflections of speech.
Also known as Auditory Comprehension Disorder; Auditory Inattention; Auditory Processing Disorder; Psychoacoustical Disorders; Acoustic Perceptual Disorders; Auditory Comprehension Disorders; or Auditory Inattentions.

Auditory processing disorder (APD) or Central APD (CAPD)

A group of mixed and poorly understood listening problems.
The major characteristic of CAPD is that the person has difficulty in understanding speech especially in difficult environments (such as degraded speech, or speech when there is background noise)

Auditory threshold

The audibility limit of discriminating sound intensity and pitch.

Augmentative and Alternative communication

Any approach designed to support, enhance, or supplement the communication of individuals who are not independent verbal communicators in all situations.
Use of forms of communication other than speaking, such as: sign language, "yes, no" signals, gestures, picture board, and computerized speech systems to compensate (either temporarily or permanently) for severe expressive communication disorders.

Austin-Moore prosthesis

A metallic unipolar femoral prosthesis used in hip hemiarthroplasties. It was one of the earliest prosthetic devices. Femoral prostheses are sometimes referred to as Moore or Austin-Moore prostheses.


A subjective sensation experienced by some individuals before the onset of a grand mal seizure.

Auropalpebral reflex (APR)

Response to sudden sound near the ear characterized by a wink or twitch at the corner of the eye.

Autism or Autism Spectrum Disorder

Autism spectrum disorder (also called autism) is a neurological and developmental disorder that usually appears during the first three years of life.
Autism (or ASD) is a wide-spectrum disorder. This means that no two people with autism will have exactly the same symptoms. As well as experiencing varying combinations of symptoms, some people will have mild symptoms while others will have severe ones.
A child with autism appears to have difficulty interacting with others, showing little interest in others, and a lack of social awareness. The focus of an autistic child is a consistent routine and includes an interest in repeating odd and peculiar behaviors. Autistic children often have problems in communication, avoid eye contact, and show limited attachment to others.
Autism can prevent a child from forming relationships with others (in part, due to an inability to interpret facial expressions or emotions). A child with autism may resist cuddling, play alone, be resistant to change, and/or have delayed speech development. Persons with autism may exhibit repeated body movements (such as flapping hands or rocking) and have unusual attachments to objects. However, many persons with autism may demonstrate proficiency in some areas (i.e., counting, measuring, art, music, memory).


A uniquely-derived character state. An apomorphy that is unique to a single terminal taxon.

Autocatalytic reaction

A reaction requiring no further additions or changes of environment to continue to completion.

Autogenesis model

A model proposing that eukaryotic cells evolved by the specialization of internal membranes originally derived from prokaryotic plasma membranes.

Autoimmune disease

A process in which the body's immune system causes illness by mistakenly attacking healthy cells, organs, or tissues in the body that are essential for good health.
Multiple sclerosis is believed to be an autoimmune disease, along with systematic lupis erythematosus, rheumatoid arthritis, scleroderma, and many others. The precise origin and pathophysiologic processes of these diseases are unknown.


Taken from an individual's own tissues, cells, or DNA.

Automatic phasic bite release pattern

A response to tactile input presented to the biting surfaces of the gums or teeth composed of a small, rhythmical series of up/down jaw movements.
Occurs until approximately 5 months of age.


Fusion of nuclei or cells derived from the same parent to yield homozygous offspring.

Autonomic nervous system

A subdivision of the nervous system of vertebrates that regulates the internal environment; consists of the sympathetic and parasympathetic divisions.

Autonomous replication sequence (ARS)

A segment of a DNA molecule necessary for the initiation of its replication.
Generally a site recognized and bound by the proteins of the replication system.

Autonomous specification

Determination of cell fate by cytoplasm acquired during cleavage, independent of interactions with neighboring cells.


polyploid formed from the doubling of a single genome.
A type of polyploid species resulting from one species doubling its chromosome number to become tetraploid, which may self-fertilize or mate with other tetraploids.


A technique that uses X- ray film to visualize radioactively labeled molecules or fragments of molecules.
A process by which radioactive materials, often though not exclusively incorporated into cell structures, are located by exposure to a photographic emulsion forming a pattern on the film corresponding to the location of the radioactive compounds within the cell.
Used in analyzing length and number of DNA fragments after they are separated by gel electrophoresis.

Autoregulation (in genetics)

The control of the transcription of a gene by its own gene product.

Autosomal dominant trait

A genetic trait carried on the autosomes.
The disorder appears when one of a pair of chromosomes contains the abnormal gene. Statistically, it is passed on from the affected parent to half of the children.

Autosomal recessive trait

A characteristic that originates from a chromosome other than the sex chromosome.
To be seen or expressed, such a trait would require the combining of two recessive genes; if paired with a dominant gene, the recessive trait would not appear. (For example, blue eyes result from the two recessive genes, but brown eyes may occur from one dominant (brown) and one recessive (blue) or two dominant genes.)


Any chromosome that is not a sex chromosome.
The diploid human genome consists of 46 chromosomes, 22 pairs of autosomes, and 1 pair of sex chromosomes (the X and Y chromosomes).
Hence Autosomal set = The non-sex chromosomes consisting of one from each homologous pair in a diploid species.


Organisms which trap energy from physical or chemical sources and use the energy to assemble the macromolecules of which they are made, through Chemosynthesis or Photosynthesis.
Photosynthesis is the only process by which this happens in eukaryotes, but additional chemosynthetic processes are found among prokaryote organisms.


Homozygosity in which the two alleles are identical by descent (ie they are copies of an ancestral gene)

Auxotrophic mutant

A nutritional mutant that is unable to synthesize and that cannot grow on media lacking certain essential molecules normally synthesized by wild-type strains of the same species.
A mutant strain of microorganism that will proliferate only when the medium is supplemented with some specific substance not required by wild-type organisms.


A measure of the association intensity of the reactions of the binder.
Avidity is influenced by all of the intrinsic ligand-binder affinities such as the multiple interactions found with polymeric antibodies and multivalent antigens binding at multiple contact points.


The mean value, which is the total amount divided by the number of data points..
The sum of a set of numbers divided by the number of numbers. Also called the arithmetic mean.

Aversion tests

Tests to determine whether and by how much a taste is rejected.

Avogadro's number (N)

The number of molecules in one mole of any compound (6.02 x 1023).

Avoidant disorder

Avoiding establishing new interpersonal contacts to the extent that social functioning is impaired.


A statement that is assumed to be true without proof; A postulate.


A vertical (ordinate) or horizontal (abscissa) dimension which intersects the other dimension at the origin of a plot.

Axis of symmetry

A line that passes through a figure in such a way that the part of the figure on one side of the line is a mirror reflection of the part of the figure on the other side of the line.


A typically long extension, or process, from a neuron that carries nerve impulses away from the cell body toward target cells.
The axon is a  filamentous process extending from the cell body of a neuron and that carries an electrical signal to synapses which are secreting chemical signaling molecules called neurotransmitters to stimulate/inhibit receiving cells. Some axons in the peripheral nervous system connecting to muscle cells or connecting sensory neurons from the skin, eye, or internal organs to the central nervous system can be quite long (measure in centimeters; 1 inch = 2.54 cm) compared to the size of an average cell (measured in micrometers).


A bundle of microtubules and other proteins forming the core of each cilium or flagellum.
A geometrically packed assemblage of microtubules (subcellular scaffolding) used to support flagella, the arms of Heliozoa, etc.

Azurophil-Derived Bactericidal Factor (ADBF)

Potent antimicrobial protein produced by neutrophils (a type of white blood cell).