Biotechnology Glossary

Biotechnology Glossary

T The thymine residue in DNA.

tag See label.

tailing The in vitro addition of the same nucleotide by the enzyme terminal transferase, to the 3´-hydroxyl ends of a duplex DNA molecule. a.k.a. homopolymeric trailing.

tandem array The existence of two or more identical DNA sequences in series, i.e., end -to-end.

tank bioreactor Vessel in which fermentation takes place. A tank bioreactor is a vessel in which a micro-organism is grown in a large volume of liquid. This contrasts with fibre or membrane bioreactors and immobilized cell reactors. The large majority of bioreactors used in biotechnology are tank bioreactors, and most tank bioreactors are stirred-tank bioreactors, because stirring helps to distribute effectively gas and nutrients to the growing organism.

tap root Root system in which the primary root has a much larger diameter than the lateral roots. Opposite: fibrous root.

Taq polymerase A heat-stable DNA polymerase isolated from the thermophilic bacterium Thermus aquaticus, and used in PCR. See polymerase.

target For diagnostic tests, the molecule or nucleic acid sequence that is being sought in a sample.

target site duplication A sequence of DNA that is duplicated when a transposable element inserts; usually found at each end the insertion.

targeted drug delivery A method of delivering a drug to the site in the body where it is needed, rather than allowing it to diffuse into many sites.

targeting vector A cloning vector carrying a DNA sequence capable of participating in a crossing-over event at a specified chromosomal location in the host cell.

TATA box A conserved adenine- and thymine-rich promoter sequence located 25-30 bp upstream of a gene, which is the binding site of RNA polymerase. See Pribnow box.

tautomeric shift The transfer of a hydrogen atom from one position in an organic molecule to another position.

tautomerism A type of isomerism in which the two isomes are in equilibrium.

T cells; T lymphocyte Lymphocyte that pass through the thymus gland during maturation. Different kinds of T cells play important roles in the immune response, being primarily responsible for the T cell-mediated response or cellular immune response.

T cell receptor An antigen-binding protein that is located on the surfaces of killer T cells and mediates the cellular immune response of mammals. The genes that encode T cell antigens are assembled from gene segments by somatic recombination processes that occur during T lymphocyte differentiation.

T-cell-mediated (cellular) immune response The synthesis of antigen-specific T cell receptors and the development of killer T cells in response to an encounter of immune system cells with a foreign immunogen.

T-DNA The segment of DNA in the Ti plasmid of Agrobacterium tumefaciens that is transferred to plant cells and inserted into the chromosomes of the plant.

T4 DNA ligase An enzyme from bacteriophage-T4-infected cells, and that catalyses the joining of duplex DNA molecules and repairs nicks in DNA molecules. The enzyme requires that one of the DNA molecules has a 5´-phosphate group and that the other has a free 3´-hydroxyl group.

tRNA; transfer RNA The class of small RNA molecules that transfer amino acids to the ribosome during protein synthesis. Transfer RNA molecules are folded into a 'clover-leaf' secondary structure by intrastrand base pairing. The anticodon loop contains a nucleotide-triplet complementary to a specific codon within the mRNA molecule. Each tRNA is 'charged' with the correct amino acid molecule, via its 3´ adenosine moiety, by an enzyme called aminoacyl-tRNA synthetase.

telomerase An enzyme that adds telomeric sequences to the ends of eukaryotic chromosomes.

telemeter The unique structure found at the end of eukaryotic chromosomes containing specialized sequences of DNA that assures the completion of a cycle of DNA replication.

telophase (Gr. telos, end + phase) The last stage in each mitotic or meiotic division, in which the chromosomes are assembled at the poles of the division spindle.

TEM See transmission electron microscope.

temperate phage A phage (virus) that invades but may not destroy (lyse) the host (bacterial cell). However, it may subsequently enter the lytic cycle.

temperature-sensitive mutant An organism that can grow at one temperature but not at another.

temperature-sensitive protein A protein that is functional at one temperature but loses function at another (usually higher) temperature.

template An RNA or single-stranded DNA molecule upon which a complementary nucleotide strand is synthesized. A pattern or mould. DNA stores coded information and acts as a model or template from which information is copied into complementary strands of DNA or transcribed into mRNA.

template strand The polynucleotide strand that a polymerase uses for determining the sequence of nucleotides during the synthesis of a new nucleic acid strand.

term finalization Repelling movement of the centromeres of bivalents in the diplotene stage of the meiotic prophase, that tends to move the visible chiasmata toward the ends of the bivalents.