Final answer:
G proteins activate enzymes such as adenylyl cyclase to increase the concentrations of small intracellular signaling molecules. This occurs through a series of steps involving the conversion of ATP to cAMP and the activation of protein kinases.
Step-by-step explanation:
Enzymes activated by G proteins can increase the concentrations of small intracellular signaling molecules through a series of steps. When a ligand binds to a G-protein linked receptor, the G-protein becomes activated and interacts with a membrane-bound enzyme called adenylyl cyclase. Adenylyl cyclase then catalyzes the conversion of ATP to cAMP, which is a small intracellular signaling molecule. cAMP activates a group of proteins called protein kinases, which transfer a phosphate group from ATP to a substrate molecule in a process called phosphorylation, leading to changes in cellular processes.