Cell Biology Terms Starting With T

Telophase is a late stage of cell division; two new nuclei form around the separated sets of chromosomes.

During telophase, the separated sets of chromosomes reach opposite poles of the cell and begin to decondense back into chromatin while nuclear envelope proteins reassemble around each chromosome set from vesicles derived from the endoplasmic reticulum. Nucleoli reappear as ribosomal RNA synthesis resumes in the nucleolar organizing regions of specific chromosomes. The spindle fiber apparatus begins to disassemble as tubulin subunits are recycled.

Telophase overlaps with cytokinesis, the physical division of the cytoplasm, which occurs through different mechanisms in animal and plant cells.

Tight Junction tight junction is a seal between neighboring cells that controls which substances can pass through the space between them.

Tight junctions consist of claudin and occludin proteins that form seals between adjacent epithelial cells by binding to homologous proteins on neighboring cells, creating a barrier that prevents paracellular transport between cells. These junctions are anchored to the cytoskeleton through zonula occludens proteins and are particularly abundant in epithelia that require selective permeability such as the intestinal lining and blood-brain barrier. The tightness of junctions can be modulated by signaling pathways, allowing cells to regulate which substances leak between cells based on physiological demands.

Different claudin subtypes in different tissues create tight junctions with varying degrees of selectivity.

Tonoplast tonoplast is the membrane surrounding the large central vacuole of a plant cell that controls the movement of substances into and out of the vacuole.

The tonoplast is a selectively permeable membrane that contains aquaporins, ion transporters, and antiporters that regulate osmotic potential and ionic balance within the plant cell vacuole. Major tonoplast transporters pump protons into the vacuole to maintain a pH of approximately 4 to 6, and secondary transporters use this proton gradient to accumulate sugars, amino acids, and other nutrients. The tonoplast also contains channels that allow calcium to be released from vacuolar stores during cell signaling.

Water moves across the tonoplast in response to osmotic gradients, controlling turgor pressure that maintains cell rigidity and shape.

Tubulin is a protein that forms long, hollow tube-shaped structures called microtubules by linking together in chains, which helps move chromosomes during cell division in organisms like fruit flies and humans.

Tubulin proteins pair up as alpha-tubulin and beta-tubulin heterodimers that polymerize end-to-end to form hollow microtubule cylinders 25 nm in diameter. GTP hydrolysis drives a dynamic instability cycle in which microtubule ends switch between growth and rapid shrinkage. Cells regulate tubulin polymerization through post-translational modifications such as acetylation, tyrosination, and polyglutamylation, which alter how motor proteins recognize different microtubule populations.