Quizbowl science/Biology/cAMP

Cyclic AMP is a G-protein coupled receptor.

How it works
The G protein-coupled receptor is attached to the G protein. When the hormone activates the GPCR, the G-alpha subunit detaches, and the GDP inside of it turns into GTP. Then, the G-alpha subunit attaches to an effector enzyme, which then triggers the release of many secondary messengers.

This case
The effector enzyme is known as adenylate cyclase. Adenylate cycloase converts ATP -> cAMP + PP. cAMP activates cAMP-dependent protein kinases.

Kinases add phosphate groups from ATP to something. So, cAMP-dependent protein kinases phosphorylate target proteins (typically cellular enzymes).

Breakdown
cAMP is broken down to AMP by cyclic nucleotide phosphodiesterase. However, this enzyme is inhibited by caffeine, thus causing stimulating effects.