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Reaction rate constant (first-order).Slope of the logarithm of product concentration (log S) versus time.


The dissociation equilibrium constant for an agonist. It is difficult to determine experimentally, since it does not necessarily equal the concentration which produces half-maximal response nor the concentration which occupies 50% of the receptors (see efficacy). It may be measured by Furchgott analysis; alternatively, if assay conditions are identical, it may equal the Ki value determined in a binding assay. The reciprocal is called the affinity constant or association constant. Do not confuse with the physicochemical use of the same symbol. For more detailed information, see Jenkinson (1989)

Kallmann's syndrome

A form of hypogonadism that is caused by congenital gonadotropin-releasing hormone (GnRH) deficiency. More common in males.

K antigen

Any of many antigens that are part of a bacterial capsule or form on the outer portion of a cell wall.

Karl Fischer titration

Titration method for determining the water content of samples using a pair of platinum electrode and a reagent containing iodine, sulfur dioxide, pyridine, and methanol. A polarizing current is applied to the electrodes and the resultant potential is measured. Most pH/mv meters are equipped on the rear panel with a pair of connectors which provide a 10 microampere current continuously during the titration.

Karvonen Formula

A formula to measure the maximum heart rate to be used in determining a target heart rate for exercise intensity for a specific subject. The Karvonen is used as a measure of heart rate reserve for calculating a target
One of the most effective methods used to calculate target heart rate for an exercise bout. It factors in resting heart rate (RHR), a quite reliable indicator of state of fitness.

  1. 220 - (Age) = Maximum Heart Rate (MaxHR)
  2. MaxHR - (resting heart rate) = Heart Rate Reserve (HRR)

To calculate target heart rate for an exercise bout it is then necessary to factor the required intensity of exercise generally based on a ranking of exercise fitness such as:
Beginners - 50-60% of HRR
Intermediate or average - 60-70% of HRR
Advanced - 75-85% of HRR


A process of fusion of the nuclei of two cells; the second step in syngamy.


Division of the nucleus during the cell cycle.


The condition of a cell's nucleus being abnormally enlarged (i.e., for reasons other than it being polyploid).


Another word for Nucleus.


A method of organizing the chromosomal characteristics of a cell in relation to number, size, and type; The number and ordering of eukaryotic chromosomes according to size and appearance.
Displayed as a photomicrograph of an individuals chromosomes arranged in a standard format showing the number, size, and shape of each chromosome type; used in low- resolution physical mapping to correlate gross chromosomal abnormalities with the characteristics of specific diseases.
The karyotype of an organism is a conserved feature and any changes in number and size of chromosomes are mutations that cause severe diseases and birth defects and are commonly lethal. The importance of chromosome structure is found in the spatial organization of genes on chromosomes, which has been found to be influencing when genes can be expressed, i.e., used to make a protein or functional RNA (see also 'epigenetics').

Kawasaki disease (mucocutaneous lymph node syndrome)

A children's illness characterized by fever, rash, swelling of the hands and feet, irritation and redness of the whites of the eyes, swollen lymph glands in the neck, and irritation and inflammation of the mouth, lips and throat. These immediate effects of Kawasaki disease are rarely serious; however, long-term heart complications result in some cases and can be seen as early as two weeks after onset of the disease.
The heart may be affected in as many as one of five children who develop Kawasaki disease. Damage sometimes occurs to the blood vessels that supply the heart muscle (the coronary arteries) and to the heart muscle itself. A weakening of a coronary artery can result in an enlargement or swelling of the blood vessel wall (an aneurysm). Infants less than 1 year old are usually the most seriously ill and are at greatest risk for heart involvement. The acute phase of Kawasaki disease commonly lasts 10 to 14 days or more. Most children recover fully. The likelihood of developing coronary artery disease later in life is not known, and remains the subject of medical investigation.


The dissociation equilibrium constant for a competitive antagonist; the concentration which would occupy 50% of the receptors at equilibrium. The reciprocal is called the affinity constant or the association constant.


The dissociation constant for a radiolabelled drug determined by saturation analysis. The units are moles per litre, and it is the concentration of drug which, at equilibrium, occupies 50% of the receptors. Its reciprocal is called the affinity constant, sometimes abbreviated to Kaff. (See kinetics of binding).

k1 or k+1

The rate constant for association of a drug with its receptor. (See kinetics of binding). The units are M-1 sec-1.


The rate constant for dissociation of a drug from its receptor. (See kinetics of binding). The units are sec-1.


A fibrous protein that fills mature keratinocytes near the skin's surface. One of a group of tough, fibrous proteins formed by certain epidermal tissues and especially abundant in skin, claws, hair, feathers, and hooves.


The basic cell type of the epidermis. Produced by basal cells in the inner layer of the epidermis


Deposition of bilirubin in the brain.  May cause damage to the basal ganglia and hippocampus. The associated diagnosis with hernicterus is athetoid cerebral palsy.


A diabetic condition that results in dehydration, vomiting, drowsiness, labored breathing, and frequent urination. Results from the accumulation of ketones in the body.


Break down product of fat that accumulates in the blood as a result of inadequate insulin or inadequate calorie intake.

Keystone predator

A predatory species that helps maintain species richness in a community by reducing the density of populations of the best competitors so that populations of less competitive species are maintained.

Keystone species

A species that is of exceptional importance in maintaining the species diversity of a community; when a keystone species is lost, the diversity of the community decreases and its structure is significantly altered.


The inhibition constant for a drug; the concentration of competing ligand in a competition assay which would occupy 50% of the receptors if no radioligand were present. Whereas the IC50 value for a compound may vary between experiments depending on radioligand concentration, the Ki is an absolute value. It is calculated from the IC50 using the Cheng-Prusoff equation:

               Ki =   ------------
                      1 + ([L]/KD)

where [L] = the concentration of free radioligand used in the assay, and KD = the dissociation constant of the radioligand for the receptor. The Ki value for an antagonist should theoretically equal the KB value determined in an in vitro experiment where a functional response is measured, provided that assay conditions are similar.


In vertebrates, the organ that regulates the balance of water and solutes in the blood and the excretion of nitrogenous wastes in the form of urine.

Kidney (or renal) cortex

The outer part of the kidney

Kidney (or renal) medulla

The inner part of the kidney

Kidney stone

Hard pebble-like mass commonly composed of calcium oxalate that forms within the kidney. Some kidney stones cause pain and must be removed using surgery or ultrasound techniques.


one thousand grams.

Kilowatthour (KWH)

a power demand of 1,000 watts for one hour. Power company utility rates are typically expressed in cents per kilowatt-hour.

Kilobase (kb)

Unit of length for DNA fragments equal to 1000 nucleotides.

Kilocalorie (kc)

A thousand calories; the amount of heat energy required to raise the temperature of 1 kg of water 1°C.


A protein which phosphorilates (adds phosphorous) to a wide variety of substances.
In molecular biology, it has acquired the more specific verbal usage for the transfer onto DNA of a radiolabeled phosphate group. This would be done in order to use the resultant "hot" DNA as a probe. There are two broad classes of kinases: serine/threonine-specific and tyrosine-specific.


An experimentally induced process in which a repeated focal application of an initially subconvulsive electrical stimulus ultimately results in a partial or generalised seizure. A technique used to study the generation and progression of epilepsy and spreading cortical depression.

Kinetics of binding

The simplest assumption about the nature of the binding of drugs to receptors is that one molecule of drug (D) binds reversibly to one receptor molecule (R) to form a drug-receptor complex (DR):

D + R <=====> DR

The rate of the forward reaction is equal to k1[D][R], where k1 is the association rate constant. (The square brackets signify the concentration of the terms they enclose). The rate of the reverse reaction equals k-1[DR], where k-1 is the dissociation rate constant. At equilibrium, the rate of association equals the rate of dissociation, i.e.

                      k1[D][R] = k-1[DR]

or, rearranging,

                      k-1         [D][R]
                     ____  = KD = ______
                      k1           [DR]

KD, the dissociation constant, may thus be defined either as the ratio of the dissociation and association rate constants, or as the concentration of drug which, at equilibrium, occupies 50% of the receptors (i.e. [DR] = [R], so KD = [D]).

Kinesin - 1

A mechanochemical protein capable of utilizing chemical energy from ATP hydrolysis to generate mechanical force. In the presence of ATP, Kinesin-1 can bind to and move on microtubules
Previously referred to as conventional kinesin, kinesin heavy chain or KHC.
The ability to translocate along the microtubule lattice has led to the classification of Kinesin-1 as a microtubule motor protein. Kinesin-1 is unrelated in sequence to the other known class of microtubule motor proteins, the dyneins, and is thought to perform functions in the cell distinct from the dyneins.

Kinesin related proteins (KRPs)

The KRPs are related to kinesin by sequence similarity to the motor domain, a region of ~340 residues that consists of an ATP-binding site and an adjacent microtubule-binding site.
Proteins related to kinesin were first reported in early 1990, soon after the entry into the databases of the first kinesin protein to be cloned, kinesin heavy chain of Drosophila. The KRPs are related to kinesin by sequence similarity to the motor domain, a region of ~340 residues that consists of an ATP-binding site and an adjacent microtubule-binding site. The proteins typically show >35% sequence identity to the kinesin heavy chain motor domain but differ in amino acid sequence outside the motor domain. The sequence difference outside the motor domain is attributed to differences in function of the KRPs compared to kinesin.
Kinesin superfamily proteins (KIFs) are well known to be involved in intracellular transport and cytokinesis. Several of the KRPs have been demonstrated to be microtubule motor proteins that bind to and move on microtubules in in vitro motility assays. The motility characteristics of many of the proteins differ significantly from kinesin: the proteins differ from kinesin in velocity, and some of them have been found to move on microtubules with the opposite polarity as kinesin, toward microtubule minus instead of plus ends. Reversed polarity has been reported for members of the C-terminal motor subfamily.
The cellular functions of the KRPs differ from those of kinesin, based on mutant analysis and localization. Several of the kinesin subfamilies, including KHC, Unc-104 and KRP85/95, have roles in vesicle/organelle transport. Evidence for transport of different types of vesicles/organelles by different classes of kinesin proteins is beginning to emerge. Strikingly, a large number of the KRPs are involved in spindle function and chromosome motility in mitosis and meiosis. These proteins could account for many of the movements of the spindle and chromosomes during cell division.
A new member of this family, KIF26A, has a novel function in that it controls proliferation of enteric neural precursor cells by directly modulating GDNF-Ret signaling. Instead of playing a role in transport, this atypical kinesin regulates a cell growth signaling pathway.


A change in activity rate in response to a stimulus.


The sensory awareness of body parts as they move.

Kinetic analysis

A kinetic analysis measures the change in concentration of the starting and end products in a ligand-binder reaction or an enzyme-substrate reaction over time.

Kinetic energy

Energy which results from a particle being in motion, which is directly related to the speed of that motion. Moving matter does work by transferring some of its kinetic energy to other matter. Contrast to Potential energy which a body possesses by virtue of being.

Kinetic molecular theory (KMT)

A theory used to explain the motion and closeness of particles to one another; used to explain states of matter.


A specialized region on the centromere that links each sister chromatid to the mitotic spindle.


Kinetics is the science of measuring changes, of assessing rates of movements and flow. In biology, kinetics is concerned with enzyme kinetics, the rate of how proteins help catalyze a chemical reactions. Another application of kinetics is the rate of flow of molecules in solution by diffusion or in an energy field (such as charges in an electric field, or mass in a gravitational field). Flux rates of molecules across biological membranes are also studied by kinetics.


The highest level of taxonomic classification containing one or more Phyla.

Kin selection

A phenomenon of inclusive fitness, used to explain altruistic behavior between related individuals.


Gram-negative rods occur in human feces and clinical specimens, soil, water, grain, fruits, and vegetables.  Some species are opportunistic pathogens.

Klinefelter's syndrome

The most common congenital abnormality in males causing primary hypogonadism.
Occurs in approximately 1 in 1000 live male births. This syndrome is the clinical manifestation of a male who has an extra X chromosome.


Gram-negative rods occur in food, soil, sewage, and human clinical specimens.
They are infrequently opportunistic pathogens.

Knock down

Usually associated with a technique used to knock out a gene's expression but does not knock out expression completely.
RNAi (Interfering RNA) is sometimes considered a knock down technique.

Knock out

In brief, the process of purposely removing (“knocking out”) a particular gene or trait from an organism; a technique for deleting, mutating or otherwise inactivating a gene in a mouse.
Refers to one of the following:

  • The engineered alteration of a particular gene within an organism, so that organism loses a (specific) function (e.g., the ability to produce a given needed clotting factor in its blood, the ability to produce a given allergen in its seeds, etc.).
  • The altered organism itself (i.e., in which the particular gene has been inactivated as detailed above).
  • The engineered alteration of a particular protein (e.g., within an organism's cell) so that protein loses its biological activity. That can enable detailed study of which proteins within a cell are responsible for particular diseases, etc.

This laborious method involves transfecting a crippled gene into cultured embryonic stem cells, searching through the thousands of resulting clones for one in which the crippled gene exactly replaced the normal one (by homologous recombination), and inserting that cell back into a mouse blastocyst. The resulting mouse will be chimaeric but, if lucky, its germ cells will carry the deleted gene. A few rounds of careful breeding can then produce progeny in which both copies of the gene are inactivated.
'Gene knockout' can be accomplished via any one of several different methods / technologies; such as gene silencing, cosuppression, site-directed mutagenesis (SDM), short interfering RNA (siRNA), etc.
'Protein knockout' can be accomplished via any one of several different methods/technologies; such as laser inactivation, etc.

Koch’s postulates

A set of four criteria for determining whether a specific pathogen is the cause of a disease.


A parasitoid that permits its host to continue to feed, grow, and function after parasitism. Compare to idiobiont.

Krebs cycle

A chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules to carbon dioxide; occurs within the mitochondrion; the second major stage in cellular respiration.


The Kruskal-Wallis test is a nonparametric analysis of variance which ranks the values of two or more sample groups from lowest to highest and then compares the distribution of these ranks to determine if one or more of the groups are significantly different from the others.

K selection

The concept that in certain (K-selected) populations, life history is centered around producing relatively few offspring that have a good chance of survival.


Gram-positive rods \widely distributed in the environment, and are common in animal feces and meat products.


Kurtosis is a measurement of the peakedness (broad or narrow) of a frequency distribution.

Kirschner wires- K wires

The commonly used designation for Kirschner wires. These are thin wires that used for a variety of purposes. They can act as fixation devices for small bones, as guide wires for insertion of cannulated nails, and as accessory components with external fixation devices.


An abnormal curvature of the spine in which both kyphosis and scoliosis are present


An abnormal curvature of the upper spine in which there is a greater posterior to anterior curve, resulting in a “”hump back”” appearance