What is the role of cyclic AMP (cAMP) as a signaling molecule?

Cyclic AMP (cAMP) serves as a crucial secondary messenger in various signal transduction pathways. When a signaling molecule, such as a hormone or neurotransmitter, binds to a receptor on the cell surface, it often activates an enzyme known as adenylyl cyclase. This enzyme catalyzes the conversion of ATP to cAMP.

Once produced, cAMP diffuses throughout the cell and activates specific protein kinases, such as protein kinase A (PKA). These kinases then phosphorylate target proteins, leading to a variety of cellular responses, such as changes in gene expression, metabolism, and cell division. The ability of cAMP to relay and amplify signals from the outside to the inside of the cell illustrates its critical role as a secondary messenger in cellular signaling pathways.

The other options describe processes that do not align with the function of cAMP. It does not inhibit signaling pathways, it does not directly catalyze enzymatic reactions as a primary function (instead, it activates other enzymes), and it does not bind directly to DNA. Understanding cAMP's role as a secondary messenger is essential for comprehending how extracellular signals translate into cellular responses.