What occurs when a receptor activates a G-protein?

What occurs when a receptor activates a G-protein?

• A. The alpha unit exchanges GDP for GTP, the beta-gamma subunit dissociates from the alpha, and the effector is activated
• B. The alpha-Beta-Gamma complex hydrolyzes GTP to GDP and reassembles
• C. The receptor directly opens an ion channel without G-protein involvement
• D. Beta-gamma subunit inhibits the alpha subunit

Answer: (A)

When a receptor activates a G-protein, the alpha subunit swaps GDP for GTP, which turns it on. This causes the alpha subunit to separate from the beta-gamma pair, and both parts can then regulate downstream effectors to propagate the signal. After signaling, the alpha subunit hydrolyzes GTP to GDP and reassembles with the beta-gamma complex to reset the system. The other options don’t fit the initial activation step: hydrolysis and reassembly happen after activation, not during the initial signal; directly opening an ion channel without G-protein involvement describes a different (ligand-gated) mechanism; and beta-gamma doesn't simply inhibit the alpha subunit—instead, the dissociated subunits go on to regulate various targets.

When a receptor activates a G-protein, the alpha subunit swaps GDP for GTP, which turns it on. This causes the alpha subunit to separate from the beta-gamma pair, and both parts can then regulate downstream effectors to propagate the signal. After signaling, the alpha subunit hydrolyzes GTP to GDP and reassembles with the beta-gamma complex to reset the system.

The other options don’t fit the initial activation step: hydrolysis and reassembly happen after activation, not during the initial signal; directly opening an ion channel without G-protein involvement describes a different (ligand-gated) mechanism; and beta-gamma doesn't simply inhibit the alpha subunit—instead, the dissociated subunits go on to regulate various targets.