Final answer:
G-protein coupled receptors are integral membrane proteins involved in cell signaling. They activate G-proteins upon ligand binding, leading to a series of intracellular events. GPCRs are characterized by seven transmembrane domains and are vital for various physiological functions.
Step-by-step explanation:
G-protein coupled receptors (GPCRs) play a critical role in cell signaling. When a signaling molecule, also known as a ligand, binds to a GPCR, it causes the receptor to undergo a structural change. This change allows the GPCR to activate an associated G-protein by facilitating the exchange of guanosine diphosphate (GDP) for guanosine triphosphate (GTP) on the G protein's alpha (α) subunit. The activated G-protein can then interact with other membrane proteins such as ion channels or enzymes, triggering a cascade of intracellular events.
GPCRs are characterized by their seven transmembrane domains, distinct extracellular ligand-binding domains, and intracellular G-protein-binding sites. After the activation event, the GTP on the G-protein's α subunit is hydrolyzed back to GDP, which leads to the deactivation of the G-protein. The deactivated subunits reassociate, and the GPCR is ready to initiate the cycle again. This process is used in numerous physiological functions, including vision, taste, immune regulation, and inflammation. Notable examples of G-protein involvement include the reception of peptide hormones, where the interaction leads to the production of intracellular second messengers like cyclic AMP (cAMP), inositol 1,4,5-triphosphate (IP3), and the calcium-calmodulin system.