Final answer:
After activation by the G protein alpha subunit, the enzyme adenylate cyclase converts ATP to cAMP, which in turn activates protein kinases leading to various cellular responses. The GTP bound to the alpha subunit is subsequently hydrolyzed, inactivating it, and the G protein complex is reassembled for reuse.
Step-by-step explanation:
After an enzyme is activated by an alpha subunit of the G protein, a series of events are set in motion within the cell, which leads to a cellular response.
The activated alpha subunit can interact with different effectors, such as adenylate cyclase, which converts ATP to cyclic AMP (cAMP). The cAMP then acts as a secondary messenger, activating protein kinases that phosphorylate proteins, thereby altering their activity and causing changes in gene transcription, or in some cases, triggering the release of Ca2+ ions that serve as another type of secondary messenger.
Eventually, the GTP bound to the activated alpha subunit is hydrolyzed back to GDP, returning the alpha subunit to its inactive form. The alpha subunit then reassociates with the beta and gamma subunits to complete the cycle, allowing the G protein to be ready for another round of signaling. The entire process is a cyclic event that controls various physiological responses depending on the type of cell and the signaling pathway involved.