Final answer:
G-proteins are activated for a short duration, typically seconds to minutes, upon ligand binding to a G-protein-linked receptor and GTP binding to the G-protein. The active state allows cellular responses until GTP is hydrolyzed to GDP, turning the G-protein inactive.
Step-by-step explanation:
G-proteins remain active as long as they are bound to guanosine triphosphate (GTP), which typically occurs for a few seconds to minutes depending on the cell type and the G-protein involved. Once activated by a ligand binding to its associated G-protein-linked receptor, the G-protein undergoes a conformational change, releases guanosine diphosphate (GDP), and binds GTP instead.
This activated state allows the G-protein subunits, specifically the alpha (a) subunit and the beta-gamma (By) complex, to interact with downstream effectors such as enzymes or ion channels, leading to cellular responses. The activity of G-proteins is terminated when the GTP bound to the alpha subunit is hydrolyzed to GDP, making the G-protein inactive and ready to start the cycle anew once another ligand binds the receptor.
G-protein-coupled receptor (GPCR) signaling is crucial for numerous physiological processes, including vision, taste, immune response, and inflammation regulation. As GPCR-mediated signaling is a cyclic process, G-proteins' activation duration is brief but sufficient to propagate a signaling cascade inside the cell.