Practice question

Seven-transmembrane receptor family also termed heptahelical receptors or G protein-coupled receptors comprises largest receptor superfamily in human genome over eight hundred members including rhodopsin-like class A, secretin class B and glutamate class C. Architecture consists of extracellular N-terminal domain ligand binding, seven hydrophobic alpha-helices TM1 through TM7 each nineteen to twenty seven residues traversing membrane with three extracellular loops ECL1-3 and three intracellular loops ICL1-3 and intracellular helix eight parallel to membrane interacting with heterotrimeric G proteins alpha beta gamma. Agonist binding in orthosteric pocket between helices induces conformational change outward movement of transmembrane helix six about six angstroms opening cavity accommodating C-terminal alpha five helix of G-alpha triggering GDP release GTP binding dissociation of beta gamma dimer activating adenylyl cyclase generating cAMP, phospholipase C beta generating inositol trisphosphate and diacylglycerol calcium mobilization, RhoGEFs activating cytoskeleton. Band 3 anion transporter, aquaporin water channel tetramer, spectrin filamentous cytoskeletal spectrin repeat protein contrast with seven-pass signaling architecture.