20. Which of the following best describes the function of the transducer in G protein-coupledreceptor (GPCR) signaling?
(A) G protein binds to extracellular ligands and triggers a conformational change in the GPCR
(B) G protein catalyzes the conversion of GTP to GDP, which in turn activates downstream effectors
(C) G protein couples the activated GPCR to downstream effector proteins, such as ion channels orenzymes
(D) G protein acts as an intracellular signaling molecule that mediates the effects of GPCR activationon gene expression