type III secretion system   One of several secretion systems in Gram negative bacteria; delivers effector proteins into host cells in a contact-dependent manner. (Figure 23–7) type IV collagen   An essential component of mature basal laminae consisting of three long protein chains twisted into a ropelike superhelix with multiple bends. Separate molecules assemble into a flexible, felt-like network that gives the basal lamina tensile strength.
tyrosine kinase Enzyme that phosphorylates specific proteins on tyrosines. See also cytoplasmic tyrosine kinase.
tyrosine-kinase-associated receptor   Cell-surface receptor that functions similarly to RTKs, except that the kinase domain is encoded by a separate gene and is noncovalently associated with the receptor polypeptide chain.
ubiquitin   Small, highly conserved protein present in all eukaryotic cells that becomes covalently attached to lysines of other proteins. Attachment of a short chain of ubiquitins to such a lysine can tag a protein for intracellular proteolytic destruction by a proteasome. (Figure 3–69) ubiquitin ligase Any one of a large number of enzymes that attach ubiquitin to a protein, often marking it for destruction in a proteasome. The process catalyzed by a ubiquitin ligase is called ubiquitylation. (Figure 3–71) unfolded protein response   Cellular response triggered by an accumulation of misfolded proteins in the endoplasmic reticulum. Involves expansion of the ER and increased transcription of genes that code for endoplasmic reticulum chaperones and degradative enzymes. (Figure 12–51) uniporter   Carrier protein that transports a single solute from one side of the membrane to the other. (Figure 11–8)
V(D)J recombination   Somatic recombination process by which gene segments are brought together to form a functional gene for a polypeptide chain of an immunoglobulin or T cell receptor. (Figure 24–28) vacuole Large fluid-filled compartment found in most plant and fungal cells, typically occupying more than a third of the cell volume. (Figure 13–41) van der Waals attraction   Type of (individually weak) noncovalent bond that is formed at close range between nonpolar atoms. (Table 2–1, p. 45 and Panel 2–3, pp. 94–95) variable region Region of an immunoglobulin or T cell receptor polypeptide chain that is the most variable and contributes to the antigen-binding site. (Figures 24–25 and 24–32) vascular endothelial growth factor (VEGF) Secreted protein that stimulates the growth of blood vessels.  (Table 15–4, p. 850, and Figure 22–26) vesicle transport model One hypothesis for how the Golgi apparatus achieves and maintains its polarized structure and how molecules move from one cisterna to another. This model holds that Golgi cisternae are long-lived structures that retain their characteristic set of Golgi-resident proteins firmly in place, and cargo proteins are transported from one cisterna to the next by transport vesicles.
vesicular transport   Transport of proteins from one cell compartment to another by means of membrane-bounded intermediaries such as vesicles or organelle fragments.
V gene segment A DNA sequence encoding most of the variable region of an immunoglobulin or T cell receptor polypeptide chain. There are many different V gene segments, one of which becomes joined to a D or J gene segment by somatic recombination when an individual lymphoid progenitor cell begins to differentiate into a B or T lymphocyte.  (Figure 24–28) virulence factor   Protein, encoded by a virulence gene, that contributes to an organism’s ability to cause disease.
virulence gene   Gene that contributes to an organism’s ability to cause disease.