Final answer:
GTP-binding proteins, or G-Proteins, are vital in signal transduction, interacting with cell membrane receptors to transmit external signals into cellular responses. These proteins go through a cycle of activation and deactivation regulated by GDP and GTP interactions with the alpha subunit, ultimately controlling various cellular processes.
Step-by-step explanation:
GTP-binding proteins (G-Proteins) are molecular switches involved in transmitting signals from various stimuli outside a cell to its interior. When a hormone or signaling molecule binds to a receptor on the plasma membrane, an allosteric change allows the receptor to interact with a G-protein on the inner plasma membrane surface. G-Proteins consist of three subunits: alpha (α), beta (β), and gamma (γ). This heterotrimeric protein complex functions in a cyclic series of events in cell signaling using G-protein-linked receptors.
Initially, the G-protein is inactive with GDP bound to its α subunit. The binding of a signaling molecule to the G-protein-coupled receptor induces a replacement of GDP with GTP on the α subunit. This exchange causes the β and γ subunits to dissociate from the α subunit, which activates other proteins in the cell and triggers a cellular response. The termination of the signal occurs when GTP is hydrolyzed back to GDP, rendering the α subunit inactive, and allowing the β and γ subunits to reassociate and restore the G-protein to its resting state.