The link between a first messenger and a second messenger in a cell that responds to peptide hormones is usually
A) cAMP.
B) cGMP.
C) adenylyl cyclase.
D) a G protein.
E) calcium.

Question

Quizplus · Accepted Answer

Peptide hormones typically bind to receptors on the cell surface, which activate G proteins. The G proteins then activate an enzyme such as adenylyl cyclase (AC), producing a second messenger such as cAMP. Therefore, the link between the first messenger (hormone) and the second messenger in this case is a G protein, making choice D the best answer.

The Link Between a First Messenger and a Second Messenger