Which event marks the end of the G-protein cycle and allows reassembly of the heterotrimer?

Which event marks the end of the G-protein cycle and allows reassembly of the heterotrimer?

• A. The alpha subunit dissociates from the beta-gamma to activate the effector
• B. GTP is hydrolyzed to GDP, enabling reassembly of the heterotrimer
• C. The receptor is internalized
• D. A second messenger is produced

Answer: (B)

When a G protein is activated, the alpha subunit binds GTP and dissociates from the beta-gamma complex to regulate an effector. The event that ends this signaling turn and allows reassembly of the inactive heterotrimer is the hydrolysis of GTP to GDP on the alpha subunit. Once GDP is bound, the alpha subunit returns to a high affinity for beta-gamma, reassociates with it, and the heterotrimer is reformed, resetting the system. Internalization of the receptor can dampen further activation but doesn’t directly drive reassembly of the heterotrimer. Production of a second messenger reflects downstream signaling, not the termination and reset of the G protein cycle.

When a G protein is activated, the alpha subunit binds GTP and dissociates from the beta-gamma complex to regulate an effector. The event that ends this signaling turn and allows reassembly of the inactive heterotrimer is the hydrolysis of GTP to GDP on the alpha subunit. Once GDP is bound, the alpha subunit returns to a high affinity for beta-gamma, reassociates with it, and the heterotrimer is reformed, resetting the system.

Internalization of the receptor can dampen further activation but doesn’t directly drive reassembly of the heterotrimer. Production of a second messenger reflects downstream signaling, not the termination and reset of the G protein cycle.