Advanced Placement (AP) Biology Practice Exam

cAMP serves as which type of molecule in cell signaling?

1. A receptor

2. A primary messenger

3. A second messenger

4. A transcription factor

The correct answer is: A second messenger

cAMP, or cyclic adenosine monophosphate, functions as a second messenger in cellular signaling pathways. When an extracellular signal, such as a hormone, binds to a receptor on the cell surface, it often activates an associated G protein. This G protein can then stimulate an enzyme called adenylate cyclase, which converts ATP into cAMP. Once produced, cAMP acts to transmit the signal from the receptor to various intracellular targets, leading to a cascade of cellular responses without the signaling molecule needing to enter the cell itself. This role makes cAMP a vital component in amplifying the signals from hormones and neurotransmitters, facilitating a more significant response in the target cell. As a second messenger, cAMP typically activates protein kinases, such as protein kinase A, which then phosphorylate other proteins, further propagating the cellular signal. This distinction is crucial; it highlights the role of cAMP in signal transduction, contrasting it with molecules like primary messengers, which initiate the signaling process but are not involved in the internal relay of signals. Likewise, receptors and transcription factors have separate roles in signaling pathways, primarily dealing with reception and regulation of gene expression, respectively.