Final answer:
Cell signaling using G-protein-linked receptors involves the binding of a ligand to the receptor, activation of the G-protein by the change in shape, and subsequent activation of other proteins before the cycle restarts.
Step-by-step explanation:
Cell signaling using G-protein-linked receptors occurs as a cyclic series of events.
1. Before the ligand binds, the inactive G-protein can bind to a newly revealed site on the receptor specific for its binding.
2. Once the G-protein binds to the receptor, the resulting change in shape activates the G-protein, which releases guanosine diposphate (GDP) and picks up guanosine 3-phosphate (GTP).
3. The subunits of the G-protein then split into the a subunit and the By subunit. One or both of these G-protein fragments may be able to activate other proteins as a result.
4. After a while, the GTP on the active a 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.