Question: For the α subunit of a trimeric G protein, … A. a G-protein-coupled receptor (GPCR) acts as…

A. a G-protein-coupled receptor
(GPCR) acts as a guanine nucleotide exchange factor (GEF), whereas
a regulator of G protein signaling (RGS) can act as a
GTPase-activating protein (GAP).

a GPCR acts as a GAP, whereas an RGS can act as a GEF.

C. both a GPCR and an RGS can act as
a GEF.

D. both a GPCR and an RGS can act as
a GAP.