Correct Option: D

Alpha, Beta, and Gamma are the three subunits of the G-protein. The active form is the Alpha-GTP complex. The intrinsic GTPase activity converts the bound GTP to GDP in the a - subunit, returning it to its original conformation. This results in the a - subunit diffusing from the adenylate cyclase and reassociating with the b & g subunits. Adenylate cyclase catalyses the conversion of ATP to cAMP which is then used to activate another, initially inactive, enzyme. The mutant G alpha protein with increased GTPase activity shows decreased signaling because of the group of proteins present which are specific to G alpha subunit called the regulator of G protein signaling.