RecA (RecA protein) Prototype for a class of DNA-binding proteins that catalyze synapsis of DNA strands during genetic recombination. (Figure 5–49) receptor   Any protein that binds a specific signal molecule (ligand) and initiates a response in the cell. Some are on the cell surface, while others are inside the cell. (Figure 15–3) receptor editing   Process by which a developing B cell that recognizes a self molecule changes its antigen receptors so that the cell no longer does so.
receptor serine/threonine kinase   Cell-surface receptor with an extracellular ligand-binding domain and an intracellular kinase domain that phosphorylates signaling proteins on serine or threonine residues in response to ligand binding. The TGFβ receptor is an example. (Figure 15–57) receptor tyrosine kinase (RTK) Cell-surface receptor with an extracellular ligand-binding domain and an intracellular kinase domain that phosphorylates signaling proteins on tyrosine residues in response to ligand binding. (Figure 15–43 and Table 15–4, p. 850) receptor-mediated endocytosis   Internalization of receptor– ligand complexes from the plasma membrane by endocytosis. (Figure 13–52) recombinant DNA technology Collection of techniques by which DNA segments from different sources are combined to make a new DNA, often called a recombinant DNA. Recombinant DNAs are widely used in the cloning of genes, in the genetic modification of organisms, and in the production of large amounts of rare proteins.
recycling endosome   Organelle that provides an intermediate stage on the passage of recycled receptors back to the cell membrane. Regulates plasma membrane insertion of some proteins. (Figure 13–58) red blood cell Small hemoglobin-containing blood cell of vertebrates that transports oxygen to, and carbon dioxide from, tissues. Also called an erythrocyte.
redox pair   Pair of molecules in which one acts as an electron donor and one as an electron acceptor in an oxidation– reduction reaction: for example, NADH (electron donor) and NAD+ (electron acceptor). (Panel 14–1, p. 765) redox potential   The affinity of a redox pair for electrons, generally measured as the voltage difference between an equimolar mixture of the pair and a standard reference. NADH/ NAD+ has a low redox potential and O2/H2 has a high redox potential (high affinity for electrons). (Panel 14–1, p. 765) redox reaction Reaction in which one component becomes oxidized and the other reduced; an oxidation–reduction reaction. (Panel 14–1, p. 765) reduction (verb reduce) Addition of electrons to an atom, as occurs during the addition of hydrogen to a biological molecule or the removal of oxygen from it. Opposite of oxidation.  (Figure 2–20) regulated nuclear transport   Mechanisms controlling export of mRNAs from the nucleus to the cytosol that can be used to regulate gene expression. Also includes the selective import of proteins and RNA molecules into the nucleus.
regulated secretory pathway   A second secretory pathway found mainly in cells specialized for secreting products rapidly on demand—such as hormones, neurotransmitters, or digestive enzymes—in which soluble proteins and other substances are initially stored in secretory vesicles for later release. (Figure 13–62) regulator of G protein signaling (RGS) A GAP protein that binds to a trimeric G protein and enhances its GTPase activity, thus helping to limit G-protein-mediated signaling. (Figure 15–8) regulatory site Region of an enzyme surface to which a regulatory molecule binds and thereby influences the catalytic events at the separate active site.