kanamycin An antibiotic of the aminoglycoside family that poisons translation by binding to the ribosomes.
kanr Kanamycin-resistance gene. See selectable marker.
kappa chain One of two classes of antibody light chains. See lambda chain.
karyogamy The fusion of nuclei or nuclear material that occurs during sexual reproduction. See fertilization.
karyogram A diagram representing the characteristic features of the chromosomes of a species.
karyokinesis The division of a cell nucleus. See meiosis; mitosis.
karyotype The chromosome constitution of a cell, an individual, or of a related group of individuals, as defined both by the number and the morphology of the chromosomes, usually in mitotic metaphase; chromosomes arranged in order of length and according to position of centromere; also, the abbreviated formula for the chromosome constitution, such as 47, XX + 21 for human trisomy-21 (Down's syndrome).
kb Kilobase pairs. See base pair; kilobase.
kcat The catalytic rate constant that characterizes an enzyme-catalysed reaction. The larger the kcat value, the faster the conversion of substrate into product.
kcat /Km The catalytic efficiency of an enzyme-catalysed reaction. The greater the value of kcat/Km, the more rapidly and efficiently the substrate is converted into product.
killer T cells T cells that carry T-cell receptors and kill cells displaying the recognized antigens.
kilobase (kb) A length unit equal to 1 000 base pairs of a double-stranded nucleic acid molecule. One kilobase of double-stranded DNA has a mass of about 660 kilodalton.
kilobase pairs (kb) Used interchangeably with kilobase.
kilocalorie (kcal) It is equal to 1000 cal. See calorie.
kilodalton (kDa) A unit of atomic mass equal to 1 000 daltons. See dalton.
kilojoule (kJ) It is equal to 1 000 J; 1 kcal = 4.184 kJ. See joule.
kinase An enzyme that can transfer a phosphate from a high energy phosphate such as ATP, to an organic molecule.
kinetics Dynamic processes involving motion.
kinetin (Gr. kinetikos, causing motion) One of the cytokinins, a group of growth regulators that characteristically promote cell division in plants.
kinetochores Two parallel bushlike filaments situated in the centromere of a chromosome.
kinetosome Granular cytoplasmic structure which forms the base of a cilium or flagellum. cf basal body.
kinin A substance promoting cell division. In plant systems, the prefix cyto- has been added (cytokinin) to distinguish it from kinin in animal systems.
Klenow fragment A product of proteolytic digestion of the DNA polymerase I from E. coli; it has both polymerase and 3´-exonuclease activities but not 5´-exonuclease activity.
Km A dissociation constant that characterizes the binding of an enzyme to a substrate. The smaller the value of Km, the tighter the binding of the enzyme to the substrate. Also called the Michaelis constant.
knockout An animal resulting from an embryonic stem cell in which a normal functional gene has been replaced by a non-functional form of the gene. This technique is used extensively in mice - much can be learned about the function of a gene by studying the phenotype of animals that lack the peptide product of that gene.