Question

consider this pathway and identify the second messenger:
epinephrine --> g protein - coupled receptor --> g protein --> adenylyl cyclase --> camp
camp
g protein
gtp
adenylyl cyclase
g protein - coupled receptor

Explanation:

Second messengers are small molecules and ions that relay signals received by cell - surface receptors to effector proteins. In the given pathway, epinephrine (a first messenger) binds to a G - protein coupled receptor. The G - protein is activated, which then activates adenylyl cyclase. Adenylyl cyclase catalyzes the conversion of ATP to cAMP. cAMP is a well - known second messenger that can then go on to activate other proteins (such as protein kinase A) within the cell.
G - protein is a membrane - associated protein involved in signal transduction but is not a second messenger. GTP is a nucleotide that can be involved in energy transfer and protein activation (like in G - protein activation) but is not a second messenger in this context. Adenylyl cyclase is an enzyme (a protein) that catalyzes a reaction to produce a second messenger. The G - protein coupled receptor is a cell - surface receptor, not a second messenger.

Answer:

cAMP