Question

The G protein that activates adenylyl cyclase is a

A. monomeric G protein in the Ras family that binds GTP.
B. dimeric G protein that separates into α and β subunits.
C. heterotrimeric G protein that separates into α and βγ subunits.
D. heterotrimeric G protein that separates into αβ and γ subunits.

Answer 1

Heterotrimeric G protein that separates into α and βγ subunits.

Step-by-step explanation:

G proteins that activate adenylyl cyclase are trimers of three different subunits. These are named alpha, beta and gamma subunits. The alpha subunit has a nucleotide-binding site called Gs. Binding of GTP to Gs activates it which in turn activates adenylyl cyclase. When the nucleotide-binding site of G-protein is occupied by GDP, it is inactive.

Binding of a signaling molecule such as epinephrine facilitates the displacement of bound GDP by GTP and converting the Gs into its active form. As Gs is activated, the beta and gamma subunits of Gs dissociate from the alpha subunit. The Gs with its alpha subunit and bound GTP then activates adenylyl cyclase.