What happens immediately after a signaling molecule binds to its G-protein coupled receptor (GPCR)?

A)The signaling molecule enters the cell through its GPCR and travels to the nucleus,where it acts as a transcription factor.
B)The G protein exchanges GTP for GDP,and becomes inactivated.
C)The G protein exchanges GDP for GTP,and becomes inactivated.
D)The G protein exchanges GTP for GDP,and becomes activateD.
E)The G protein exchanges GDP for GTP,and becomes activated.