TATA box   Sequence in the promoter region of many eukaryotic genes that binds a general transcription factor (TFIID) and hence specifies the position at which transcription is initiated. (Figure 6–14)
T cell receptor (TCR) Transmembrane receptor for antigen on the surface of T lymphocytes, consisting of an immunoglobulin-like heterodimer. (Figure 24–32)
T-cell-mediated immune response Any adaptive immune response mediated by antigen-specific T cells.
telomerase   Enzyme that elongates telomere sequences in DNA, which occur at the ends of eukaryotic chromosomes.
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, and meros, portion.
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. (Panel 17–1, pp. 980–981) template Single strand of DNA or RNA whose nucleotide sequence acts as a guide for the synthesis of a complementary strand. (Figure 1–3) terminal differentiation The limit of cell determination when a cell forms one of the highly specialized cell types of the adult body.
terminally differentiated A cell at the limit of cell determination, being one of the highly specialized cell types of the adult body.
terminator Signal in bacterial DNA that halts transcription; in eukaryotes, transcription terminates after cleavage and polyadenylation of the newly synthesized RNA.
tertiary structure   Complex three-dimensional form of a folded polymer chain, especially a protein or RNA molecule.
TH1 cell   A type of effector helper T cell that secretes interferon-γ to help activate macrophages and induces B cells to switch the class of antibody they make. (Figure 24–44)
TH17 cell   A type of effector helper T cell that secretes IL17, which recruits neutrophils and stimulates an inflammatory response. (Figure 24–44)
TH2 cell   A type of effector helper T cell that helps activate  B cells to produce antibodies, to undergo somatic hypermutation, and switch the class of immunoglobulin produced. (Figure 24–44) thylakoid   Flattened sac of membrane in a chloroplast that contains chlorophyll and other pigments and carries out the light-trapping reactions of photosynthesis. Stacks of thylakoids form the grana of chloroplasts. (Figures 14–35 and 14–36) thylakoid membrane   Chloroplast membrane system that contains the large membrane protein complexes for photosynthesis and photophosphorylation.
thymocytes Developing T cells in the thymus.
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. (Figures 19–2 and 19–21)
TIM complexes   Protein translocators in the mitochondrial inner membrane. The TIM23 complex mediates the transport of proteins into the matrix and the insertion of some proteins into the inner membrane; the TIM22 complex mediates the insertion of a subgroup of proteins into the inner membrane.  (Figure 12–21)
Toll   A transmembrane receptor protein. On the ventral side of the Drosophila egg membrane, its activation controls the distribution of Dorsal, a transcription regulator of the NFκB family.