juvenile hormoneA hormone secreted by insects from a pair of endocrine glands close to the brain.
juvenile in vitro embryo technology(Abbreviation: JIVT or JIVET). A technology involving collection of immature eggs from young animals, their in vitro maturation and fertilization, and the…
juvenilityEarly phase of development in which an organism is incapable of sexual reproduction.
KanamycinAn antibiotic of the aminoglycoside family that poisons translation by binding to the ribosomes.
kanrKanamycin resistance gene. (See Selectable marker.)
kappa chainOne of two classes of antibody light chains. The other is a lambda chain.
karyogamyThe fusion of nuclei or nuclear material that occurs at fertilization during sexual reproduction.
karyogramA diagrammatic representation of the full chromosome set of a species, highlighting characteristic physical features of individual chromosomes.
karyokinesisThe division of a cell nucleus. See: meiosis; mitosis.
KaryotypeAll of the chromosomes in a cell or an individual organism, visible through a microsope during cell division.
KBAbbreviation for kilobase (of single-stranded nucleic acid).
kbpAbbreviation for kilobase pairs (of double-stranded DNA ).
kcatThe catalytic rate constant that characterizes an enzyme-catalysed reaction. The larger the kcat value, the faster the conversion of substrate into…
kcat/KmThe catalytic efficiency of an enzyme-catalysed reaction. The greater the value of kcat/Km, the more rapidly and efficiently the substrate is converted…
KdAbbreviation for dissociation constant. Describes the strength of binding (or affinity) between molecules and their ligands . See: avidity.
kDaAbbreviation for kiloDalton. A unit of molecular mass equal to 1000 Dalton.
killer T cellT cells that kill cells displaying recognized antigens.
kilobase(Abbreviation: kb). A length of single-stranded nucleic acid composed of 1000 bases.
kilobase pairs(Abbreviation: kbp). A length of double-stranded DNA composed of 1000 base pairs.
kinaseAn enzyme that catalyses the transfer of a phosphate group from a high energy state (as in ATP) to another molecule.
kineticsDynamic processes involving motion. Often used as a suffix to indicate studies involving movement or rates of reactions.
kinetochoreStructure at the centromere of eukaryotic chromosomes. The kinetochore consists of inner and outer electron dense plates and a central zone containing…
kinetosomeGranular cytoplasmic structure which forms the base of a cilium or flagellum. Synonym: basal body.
kininA substance promoting cell division. In plant systems, the prefix cyto- has been added (cytokinin ) to distinguish it from kinin in animal systems.
Klenow fragmentA truncated form of DNA polymerase I from E. coli, used extensively for the production of synthetic DNA molecules as it retains polymerase and…
KmA dissociation constant that characterizes the binding of an enzyme to a substrate.
Knock InReplacement of a gene by a mutant version of the same gene using homologous recombination.
Knock OutInactivation of a gene by homologous recombination following transfection with a suitable DNA construct.
knockoutA mutant individual, in which a single functional gene has been replaced by a non-functional form of the gene.
labelThe FDA approved label is the official description of a drug product which includes indication (what the drug is used for); who should take it; adverse…
Labeling of foodsThe process of developing a list of ingredients contained in foods. Labels imply that the list of ingredients can be verified. The U.S.
labellingThe process of attaching or inserting a label into a molecule. Most often in the context of nucleic acids or protein s.
lactoseA type of sugar found in milk and milk products.
Lag phaseThe initial growth phase, during which cell number remains relatively constant prior to rapid growth. See growth phase.
lagging strandThe strand of DNA that is synthesized discontinuously during replication (because DNA synthesis can proceed only in the 5'?3' direction).
lambda chainOne of two classes of antibody light chains. The other is a kappa chain.
lambda phageA bacteriophage that infects E. coli, commonly used as a cloning vector. See: integration-excision region.
lamellaA structure, plate or vesicle that is formed by two membranes lying parallel to each other.
laminar air-flow cabinetCabinet designed for cell or tissue culture manipulations requiring a sterile environment.
laminarinA storage polysaccharide of the brown algae.
lampbrush chromosomeLarge diplotene chromosomes present in oocyte nuclei, and particularly conspicuous in amphibians.
landraceIn plant genetic resources, an early, cultivated form of a crop species, evolved from a wild population, and generally composed of a heterogeneous mixture…
latent agentA pathogen, usually a virus, present in a host organism without producing any symptoms.
latent budAn inactive bud not held back by rest or dormant period, but which may start growth if stimulated.
leader sequenceA variable length sequence of nucleotides at the 5' end of an mRNA molecule that precedes the AUG initiation codon where translation begins and is not…
leading strandThe strand of DNA that is synthesized continuously during replication.
leaf bladeThe usually flattened portion of the leaf.
leaf bud cuttingA cutting that includes a short section of stem with attached leaf.
leaf primordiumA lateral outgrowth from the apical meristem, which will become a leaf when fully developed and expanded.
leaf rollA symptom of some virus diseases, characterized by curling of the leaves. Can also occur as a response to water stress.
leaf scarMark left on a stem after leaf abscission.
leafletExpanded leaf-like part of a compound leaf.
leaky mutantA mutant in which the gene product still retains some biological activity.
lectinA complex molecule that has both protein and sugars. Lectins are able to bind to the outside of a cell and cause biochemical changes in it.
LegumeA member of the pea family that possesses root nodules containing nitrogen-fixing bacteria.
leptonemaStage in meiosis immediately preceding synapsis and post DNA replication, in which the chromosomes appear as single, fine, threadlike structures.
Leukocyte(LOO-koh-site) A white blood cell. Refers to a blood cell that does not contain hemoglobin.
libraryA collection of cells, usually bacteria or yeast, that have been transformed with recombinant vectors carrying DNA inserts from a single species.
life cycleThe sequence of events from a given developmental stage in one generation to the same stage in the following generation.
ligandA small molecule (e.g. activators, substrates and inhibitors of enzyme activity) bound to a protein by non-covalent forces; an ion or a molecule that…
Ligase (DNA ligase)An enzyme that catalyzes a condensation reaction that links two DNA molecules via the formation of a phosphodiester bond between the 3' hydroxyl and 5'…
ligase chain reaction(Abbreviation: LCR). A technique for the detection and amplification of target DNA sequences.
LigateThe process of joining two or more DNA fragments.
ligate, ligationThe joining of two linear double-stranded DNA fragments by the formation of phosphodiester bonds.
lignificationThe thickening and strengthening of a plant cell wall with lignin.
ligninA group of high-molecular-weight amorphous polymers of phenylpropanoid compounds, giving strength to certain tissues. A major component of wood.
lignocelluloseThe combination of lignin, hemicellulose and cellulose that forms the structural framework of plant cell walls.
LineageA chart that traces the flow of genetic information from generation to generation.
linear phaseThe growth phase during cell culture when cell number increases arithmetically. The linear phase follows a period of exponential growth.
linearized vectorA covalently closed circular DNA vector (typically a plasmid ) which has been opened by restriction digestion to convert it to a linear molecule.