Which step describes the alpha subunit dissociating from the beta-gamma to activate the effector?

Which step describes the alpha subunit dissociating from the beta-gamma to activate the effector?

• A. The alpha subunit dissociates from the beta-gamma subunit to activate the effector
• B. GDP is hydrolyzed to GTP
• C. The heterotrimer reassembles and recouples to the receptor
• D. GTP is hydrolyzed to GDP

Answer: (A)

Activation begins when the receptor acts as a guanine nucleotide exchange factor, causing the alpha subunit to swap GDP for GTP. This GTP binding changes the alpha subunit’s shape and drives it to dissociate from the beta-gamma dimer. The free alpha-GTP then interacts with and activates its effector, producing the cellular response. Later, the intrinsic GTPase activity hydrolyzes GTP to GDP, allowing the alpha to reassociate with beta-gamma and terminate signaling. So the step where the alpha subunit separates from beta-gamma to activate the effector is the dissociation that follows GTP binding. The other steps describe hydrolysis or reassembly, which do not account for the activation via dissociation.

Activation begins when the receptor acts as a guanine nucleotide exchange factor, causing the alpha subunit to swap GDP for GTP. This GTP binding changes the alpha subunit’s shape and drives it to dissociate from the beta-gamma dimer. The free alpha-GTP then interacts with and activates its effector, producing the cellular response. Later, the intrinsic GTPase activity hydrolyzes GTP to GDP, allowing the alpha to reassociate with beta-gamma and terminate signaling. So the step where the alpha subunit separates from beta-gamma to activate the effector is the dissociation that follows GTP binding. The other steps describe hydrolysis or reassembly, which do not account for the activation via dissociation.