An activated G protein-coupled receptor activates a G protein inside the cell, which involves the release of GDP and the binding of GTP. The activated G protein then activates an associated enzyme, leading to a cellular response.Many signal molecules, such as neurotransmitters and many hormones, act through G-protein-linked receptors. This kind of receptor spans the cell membrane, and as you might guess, it works through a protein called a G protein. When the signal molecule binds to the receptor, the receptor becomes activated. It is now able to activate a specific G protein by causing GTP to displace GDP on the G protein. The activated G protein then binds to another protein, usually an enzyme, and alters its activity. Then the G proteinhydrolyzes its GTP and reverts to its inactive form— ready to respond to another signal.