AP BIOLOGY

Detailed explanation-1: -Slow intrisinc GTP ase activity results in an inactivation of the alpha-i subunit by hydrolyzing GTP to GDP .

Detailed explanation-2: -The G-protein has three subunits, alpha, beta and gamma. Activation of the receptor by the neurotransmitter dopamine causes the alpha subunit to exchange its GDP for a GTP. The G protein then disassociates. The alpha subunit, with GTP, pulls away leaving behind the beta and gamma subunits.

Detailed explanation-3: -Whereas G proteins are activated by G protein-coupled receptors, they are inactivated by RGS proteins (for “Regulator of G protein signalling"). Receptors stimulate GTP binding (turning the G protein on). RGS proteins stimulate GTP hydrolysis (creating GDP, thus turning the G protein off).

Detailed explanation-4: -G proteins carry lipid modifications on one or more of their subunits to target them to the plasma membrane and to contribute to protein interactions. This family consists of the G protein alpha subunit, which acts as a weak GTPase.

Detailed explanation-5: -As for Ras GTPases, G is “activated” for interaction with effectors when bound to GTP, and deactivated by its intrinsic GTPase activity – which, for most G proteins, is accelerated by GTPase activating proteins or protein domains (GAPs).