Final answer:
Cell signaling using G-protein-linked receptors involves the activation and disassociation of subunits, specifically the alpha (a) subunit and the By subunit. Once activated, the alpha subunit can activate other proteins before being deactivated through GTP hydrolysis.
Step-by-step explanation:
Cell signaling using G-protein-linked receptors occurs as a cyclic series of events. Before the ligand binds, the inactive G-protein can bind to a newly revealed site on the receptor specific for its binding. Once the G-protein binds to the receptor, the resulting change in shape activates the G-protein, which releases GDP and picks up GTP.
The subunits of the G-protein then split into the subunit and the By subunit. One or both of these G-protein fragments may be able to activate other proteins as a result. After a while, the GTP on the active subunit of the G-protein is hydrolyzed to GDP and the By subunit is deactivated. The subunits reassociate to form the inactive G-protein and the cycle begins anew.