Which of the following acts as a second messenger in cell signaling pathways?

• A. Insulin
• B. cAMP (cyclic adenosine monophosphate)
• C. DNA polymerase
• D. Phospholipid bilayer

Answer: (B)

Verified step by step guidance

1. Understand the concept of second messengers: Second messengers are molecules that relay signals received at receptors on the cell surface to target molecules inside the cell, amplifying the signal and triggering a cellular response.
2. Identify the role of cAMP (cyclic adenosine monophosphate): cAMP is a well-known second messenger in many signaling pathways. It is synthesized from ATP by the enzyme adenylyl cyclase, which is activated by signaling molecules like hormones or neurotransmitters.
3. Compare the options provided: Insulin is a hormone that acts as a primary messenger, not a second messenger. DNA polymerase is an enzyme involved in DNA replication, not signaling. The phospholipid bilayer is a structural component of the cell membrane, not a signaling molecule.
4. Recognize that cAMP fits the definition of a second messenger: It is involved in transmitting signals from the cell surface to intracellular targets, such as protein kinases, to elicit a response.
5. Conclude that cAMP is the correct answer based on its role in cell signaling pathways as a second messenger.