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T lymphocyte (T cell):
Type of lymphocyte responsible for cell-mediated immunity; includes
both cytotoxic T cells and helper T cells.
TATA box:
Consensus sequence in the promoter region of many eucaryotic genes
that binds a general transcription factor and hence specifies
the position where transcription is initiated.
telomere:
End of a chromosome, associated with a characteristic DNA sequence
that is replicated in a special way. Counteracts the tendency
of the chromosome otherwise to shorten with each round of replication.
(From Greek telos, end.)
telophase:
Final stage of mitosis in which the two sets of separated chromosomes
decondense and become enclosed by nuclear envelopes.
temperature sensitive (ts) mutant:
Organism or cell carrying a genetically altered protein (or RNA
molecule) that performs normally at one temperature but is abnormal
at another (usually higher) temperature.
tertiary structure:
Complex three-dimensional form of a macromolecule, especially
a protein.
Tetrahymena:
Genus of ciliated protozoa used in studies of ciliary axonemes,
self-splicing RNA, and telomere reproduction.
thioester
bond:
High-energy bond formed by a condensation reaction between
an acid (acyl) group and a thiol group ( - SH); seen, for
example, in acetyl CoA and in many enzyme-substrate complexes.
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thiol:
see sulfhydryl
thylakoid:
Flattened sac of membrane in a chloroplast that contains
pigment and carries out the light-gathering reactions of
photosynthesis. Stacks of thylakoids form the grana of chloroplasts.
tight junction:
Cell-cell junction that seals adjacent epithelial cells
together, preventing the passage of most dissolved molecules
from one side of the epithelial sheet to the other.
topoisomerase (DNA topoisomerase):
Enzyme that makes reversible cuts in a double helical DNA
molecule for the purpose of removing knots or unwinding
excessive twists.
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