Final answer:
After GTP is hydrolyzed to GDP by the GTPase activity of the alpha subunit, the inactive alpha subunit re-associates with the beta and gamma subunits, resetting the G protein complex for the next signaling event.
Step-by-step explanation:
After the GTPase activity of the alpha subunit hydrolyzes GTP to GDP, the now inactive alpha subunit will re-associate with the beta and gamma subunits. This reassociation occurs as part of a larger cycle involving G-protein-coupled receptors (GPCRs). Initially, when a signaling molecule binds to a GPCR, it causes the GDP bound to the alpha subunit to be exchanged for GTP. This exchange activates the G protein, and the beta and gamma subunits dissociate from the alpha subunit.
Subsequently, the activated alpha subunit, carrying GTP, can trigger a cellular response. Eventually, GTP is hydrolyzed to GDP through the inherent GTPase activity of the alpha subunit, which in turn deactivates the alpha subunit. After hydrolysis, the deactivated alpha subunit reconnects with the beta and gamma subunits to form the inactive G protein, preparing the system for the next signaling event.