Rho family Family of monomeric GTPases within the Ras superfamily involved in signaling the rearrangement of the cytoskeleton. Includes Rho, Rac, and Cdc42. (Table 15–5, p. 854) rhodopsin   Seven-span membrane protein of the GPCR family that acts as a light sensor in rod photoreceptor cells in the vertebrate retina. Contains the light-sensitive prosthetic group retinol. (Figure 15–39) ribosomal RNA (rRNA) Any one of a number of specific RNA molecules that form part of the structure of a ribosome and participate in the synthesis of proteins. Often distinguished by their sedimentation coefficient (e.g., 28S rRNA, 5S rRNA).
ribosome Particle composed of rRNAs and ribosomal proteins that catalyzes the synthesis of protein using information provided by mRNA. (Figure 6–64) ribozyme   An RNA molecule with catalytic activity.
RNA (ribonucleic acid) Polymer formed from covalently linked ribonucleotide monomers. See also messenger RNA, ribosomal RNA, transfer RNA. (Figure 6–4)
RNA editing   Type of RNA processing that alters the nucleotide sequence of an RNA transcript after it is synthesized by inserting, deleting, or altering individual nucleotides.
RNA interference (RNAi) As originally described, mechanism by which an experimentally introduced double-stranded RNA induces sequence-specific destruction of complementary mRNAs. The term RNAi is often used to include the inhibition of gene expression by microRNAs (miRNAs) and piwi RNAs (piRNAs), which are encoded in the cell’s own genome.
RNA polymerase Enzyme that catalyzes the synthesis of an RNA molecule on a DNA template from ribonucleoside triphosphate precursors. (Figure 6–9)
RNA primer   Short stretch of RNA synthesized on a DNA template. It is required by DNA polymerases to start their DNA synthesis.
RNA processing control Regulation by a cell of gene expression by controlling the processing of RNA transcripts, which includes their splicing.
RNA splicing   Process in which intron sequences are excised from RNA transcripts. A major process in the nucleus of eukaryotic cells leading to formation of messenger RNAs (mRNAs).
RNA transport and localization control Regulation by a cell of gene expression by selecting which completed mRNAs are exported from the nucleus to the cytosol and determining where in the cytosol they are localized.
RNA world Hypothesis that early life on Earth was based primarily on RNA molecules that both stored genetic information and catalyzed biochemical reactions.
RNA-seq   Sequencing the entire repertoire of RNA from a cell or tissue; also known as deep RNA sequencing.
robustness   The ability of biological regulatory systems to function normally in the face of perturbations such as exposure to frequent and/or extreme variations in external conditions or the concentrations or activities of key components.
rod photoreceptor (rod) Photoreceptor cell in the vertebrate retina that is responsible for noncolor vision in dim light.
rough endoplasmic reticulum (rough ER) Endoplasmic reticulum with ribosomes on its cytosolic surface. Involved in the synthesis of secreted and membrane-bound proteins.
rRNA gene Gene that specifies a ribosomal RNA (rRNA).
ryanodine receptor   A regulated Ca2+ channel in the ER membrane that opens in response to rising Ca2+ levels and thus amplifies the Ca2+ signal.
SAM complex   Protein translocator that helps β-barrel proteins to fold properly in the outer mitochondrial membrane.
Sar1 protein   Monomeric GTPase responsible for regulating COPII coat assembly at the endoplasmic reticulum membrane.
sarcoma Cancer of connective tissue.