G-protein subunits

• A. Alpha, Beta, and Gamma
• B. Only Alpha
• C. Gamma only
• D. Delta and Epsilon

Answer: (A)

G proteins in GPCR signaling are heterotrimers, made up of three subunits: alpha, beta, and gamma. The alpha subunit binds GDP or GTP and has intrinsic GTPase activity, while the beta and gamma subunits form a beta-gamma dimer that helps regulate downstream effectors and channels. When the receptor is activated, GDP on Gα is exchanged for GTP and Gα-GTP dissociates from the beta-gamma dimer to propagate signals. The option listing all three subunits—alpha, beta, and gamma—captures this canonical structure. The other options omit one or more essential components (or refer to subunits not recognized as the standard trio in this context), so they don’t describe the functional G protein complex.