Final answer:
A G-protein coupled receptor is associated with a G protein that contains three subunits, namely alpha, beta, and gamma. Activation of this complex occurs through the exchange of GDP for GTP and results in the dissociation of the subunits, which triggers cellular responses.
Step-by-step explanation:
A G-protein coupled receptor associates with a G protein that contains three subunits: alpha (α), beta (ß), and gamma (γ). This heterotrimeric G-protein becomes activated when a signaling molecule binds to the G-protein-coupled receptor embedded in the plasma membrane. Upon activation, the GDP molecule associated with the alpha subunit is exchanged for a GTP molecule, leading to the dissociation of the beta and gamma subunits from the alpha subunit. Subsequently, a cellular response is triggered either by the activated alpha subunit or by the dissociated beta-gamma pair. Eventually, the hydrolysis of GTP back to GDP on the alpha subunit terminates the signaling event, and the subunits reassociate to return to the inactive state, ready for a new cycle.