T cellOne type of white blood cell that attacks virus-infected cells, foreign cells, and cancer cells.
T cell receptorAn antigen -binding protein, located on the surface of mammalian killer T cells, which mediates the cellular immune response.
T lymphocyteOne type of white blood cell that attacks virus-infected cells, foreign cells, and cancer cells.
T-cell-mediated (cellular) immune responseThe synthesis of antigen-specific T cell receptors and the development of killer T cells in response to an encounter of immune system cells with an…
T-DNAThe DNA segment of the Ti plasmid, present in pathogenic Agrobacterium tumefaciens, that is transferred to plant cells and inserted into the plant's DNA…
T0, T1 and T2Successive generations of plants following a transformation event. The parent transformed plant is T0, its immediate progeny is T1, and the progeny of the…
T4 DNA ligaseAn enzyme, present in bacteria infected with bacteriophage T4, which catalyses the joining (ligation ) of, and repairs nicks in, duplex DNA molecules.
tailingThe in vitro addition, to the 3'-hydroxyl ends of a double-stranded DNA molecule, of multiple copies of a single nucleotide by the enzyme terminal…
tandem repeatTwo (or more) contiguous identical DNA sequences. The orientation can be either head-to-tail, or head-to-head.
tank bioreactorA fermentation vessel designed to grow large scale quantities of a micro-organism (bacteria, yeast or fungi).
tap rootRoot system in which the primary root has a much larger diameter than any lateral roots (e.g. carrot). Opposite: fibrous root.
Taq polymeraseA heat-stable DNA polymerase isolated from the bacterium Therrnus aquaticus, used in PCR. (See Polymerase.)
TargetIn diagnostic tests, the molecule or nucleic acid sequence assayed in a sample.
target site duplicationA short sequence of DNA duplicated when a transposable element inserts at a new locus; usually found at each end of the insertion.
targeted drug deliveryA method of delivering the activated form of a drug molecule to the site in the body where it is needed, rather than allowing it reach the target by…
targeting vectorA cloning vector carrying a DNA sequence capable of participating in a recombinational event at a specified chromosomal location in the host cell.
TATA boxAn adenine- and thymine-rich promoter sequence located 25-30 bp upstream of a gene, which is the binding site of RNA polymerase.
tautomeric shiftThe transfer of a hydrogen atom from one position in an organic molecule to another position.
tautomerismA type of isomerism in which the two isomers arising from a tautomeric shift are in equilibrium.
TelomeraseAn enzyme that maintains the structure of the telomere by adding the required repetitive sequences to the ends of eukaryotic chromosomes.
terminal budA branch tip, an undeveloped shoot containing rudimentary floral buds or leaves, enclosed within protective bud scales.
terminal transferaseAn enzyme that catalyses the addition of nucleotides to the 3' end of a DNA molecule.
terminalizationRepelling movement of the centromeres of bivalents in the diplotene stage of the meiotic prophase, that appears to move visible chiasmata toward the ends…
Termination codonAny of three mRNA sequences (UGA, UAG, UAA) that do not code for an amino acid and thus signal the end of protein synthesis. Also known as stop codon.
termination signalIn transcription, a nucleotide sequence that specifies RNA chain termination.
terminator1. A DNA sequence just downstream of the coding segment of a gene, which is recognized by RNA polymerase as a signal to stop synthesizing mRNA. 2.
terminator geneA specific variety-level genetic use restriction technology. A patented technique.
Terminator regionA DNA sequence that signals the end of transcription.
tertiary structureThe three-dimensional conformation taken up by complete macromolecules as a result of intramolecular interactions, such as hydrogen-bonding.
testcrossA cross between a genetically unknown individual and a recessive tester to determine whether the individual in question is heterozygous or homozygous for…
testis(TES-tis) One of two egg-shaped glands inside the scrotum that produce sperm and male hormones. Also called testicle.
testosterone(tes-TOS-ter-own) A hormone that promotes the development and maintenance of male sex characteristics.
TetracyclineAn antibiotic drug used to treat infection.
tetradThe four haploid cells formed after the second meiotic division in plants (pollen tetrads) or fungi (ascospores).
tetraploidAn organism, or a tissue whose cells contain four haploid sets of chromosome s.
tetrasomic(Noun: tetrasome). Pertaining to a nucleus or an organism with four members of one of its chromosomes, whereas the remainder of its chromosome complement…
tetratypeIn fungi, a tetrad of spores that contains four different types; e.g. AB, aB, Ab and ab.
TGGEAbbreviation for thermal gel gradient electrophoresis.
thallusPlant body without true roots, stems, or leaves.
therapeutic agentA compound used for the treatment of a disease or for improving the well-being of an organism. Synonyms: pharmaceutical agent, drug.
Therapeutic cloningThe potential use of stem cells to grow, in vitro, tissue or organs for use in transplantation.
thermal gel gradient electrophoresis(Abbreviation: TGGE). A method for separating DNA fragments according to their mobility under increasingly denaturing conditions imposed by heat.
thermal shockExposure to reduced or increased temperature for a significant period.
thermolabileNot resistant to heat, often in the context of a molecule which is unstable upon heating. Opposite: thermostable.
thermophileAn organism which is adapted to high temperatures, such as in hot springs and geysers, smoker vents on the sea floor, and domestic hot water pipes.
thermosensitivityLoss of biological activity of a molecule at high temperature.
thermostableA molecule which retains its biological activity at some specified higher temperature. Opposite: thermolabile.
thermotherapy(THER-moh-THAYR-uh-pee) Treatment of disease using heat.
thinning1. Removal of older stems to promote new growth. 2. Removal of excess fruits to improve the size and quality of the remaining fruits. 3.
thymidineA chemical compound found in DNA. Also used as treatment for mucositis.
thymidine kinase(Abbreviation: tk). An enzyme that allows a cell to utilize an alternate metabolic pathway for incorporating thymidine into DNA.
Thymidine kinase (tk)An enzyme that allows a cell to utilize an alternate metabolic pathway for incorporating thymidine into DNA.
thymidylic acid(Abbreviation: TMP or dTMP). Synonym for thymidine 5'-monophosphate, a deoxyribonucleotide containing the nucleoside thymidine.
thymine(Abbreviation: T). One the bases found in DNA. See: thymidine.
Ti (tumor-inducing) plasmidA giant plasmid of Agrobac- terium tumefaciens that is responsible for tumor formation in infected plants.
Ti plasmidTumour-inducing plasmid. A large plasmid present in pathogenic Agrobacterium tumefaciens, responsible for the induction of tumours in plant with crown…
Tissue(TISH-oo) A group or layer of cells that work together to perform a specific function.
Tissue cultureThe in vitro culture of cell s, tissue s or organ s in a nutrient medium under sterile conditions.
titre1. The concentration of infectious virus particles present in a suspension. 2. A measure of antibody concentration, given by the highest dilution of the…
TMPAbbreviation for the deoxyribonucleotide thymidine 5'-monophosphate. See: thymidylic acid.
ToleranceA condition in which higher doses of a drug are required to produce the same effect achieved during initial use; often associated with physical dependence.
tonoplastThe cytoplasmic membrane bordering the vacuole of plant cells. It plays a prominent role in regulating the osmotic pressure exerted by the cell sap.
totipotencyThe ability of a cell or tissue to be induced to regenerate into a complete organism.
TotipotentHaving to do with cells that are able to develop into any type of cell found in the body.
Toxic Substances Control Act (TSCA)The Toxic Substances Control Act (TSCA), passed in 1976, requires tests of chemicals that may harm human health or the environment; reviews of new…
toxicity(tok-SIH-sih-tee) The extent to which something is poisonous or harmful.
toxin(TOK-sin) A poison produced by certain animals, plants, or bacteria.
tracerA substance (such as a radioisotope) used in imaging procedures.
tracheidAn elongated, tapering xylem cell, with lignified pitted walls, adapted for solute conduction and physical support.
Traditional breedingModification of plants and animals through selective breeding. Practices used in traditional plant breeding may include aspects of biotechnology such as…
trans-acting1. A term describing substances that are diffusable and that can affect spatially separated entities within cells. 2. A genetic element (e.g.
trans-acting factorAny of the multiple ancillary DNA -binding proteins that interact with the cis-regulatory DNA sequences to control gene expression.
TranscapsidationThe partial of full coating of the nucleic acid of one virus with a coat protein of a differing virus. See Coat protein.
Transcripta written copy of spoken or recorded material which is the official or legal copy of a court hearing, also called a court reporter’s transcript.
TranscriptionIn biology, the process by which a cell makes an RNA copy of a sequence of DNA that is a gene.
transcription unitA segment of DNA that contains signals for the initiation and termination of transcription, and is transcribed into one RNA molecule.
transcriptional anti-terminatorA protein that prevents RNA polymerase from terminating transcription at specific transcription termination sequences.
transcriptional roadblockA DNA -binding protein which affects the rate at which RNA polymerases transcribe genes.