Cyclic AMP functions as a second messenger to (a) build proteins and catalyze specific reactions, (b) activate adenylate cyclase, (c) open ion channels and activate key enzymes in the cytoplasm, (d) bind the hormone–receptor complex to DNA segments.

Verified step by step guidance

1. Understand the role of cyclic AMP (cAMP) as a second messenger in cellular signaling pathways.
2. Recall that second messengers like cAMP are involved in transmitting signals from receptors on the cell surface to target molecules inside the cell.
3. Consider the typical functions of cAMP, which include activating protein kinases and opening ion channels.
4. Evaluate each option: (a) building proteins and catalyzing reactions is not a direct role of cAMP; (b) activating adenylate cyclase is incorrect as adenylate cyclase produces cAMP; (c) opening ion channels and activating enzymes aligns with cAMP's role; (d) binding hormone-receptor complexes to DNA is not a function of cAMP.
5. Conclude that the correct function of cAMP as a second messenger is to open ion channels and activate key enzymes in the cytoplasm, which corresponds to option (c).

Key Concepts

Cyclic AMP (cAMP)

Cyclic AMP (cAMP) is a crucial second messenger in cellular signaling pathways. It is synthesized from ATP by the enzyme adenylate cyclase in response to various hormones and signals. cAMP transmits the effects of these signals by activating protein kinases, which then phosphorylate target proteins, leading to various cellular responses.

Second Messenger System

A second messenger system is a mechanism by which extracellular signals, such as hormones, are translated into intracellular actions. When a signaling molecule binds to a receptor on the cell surface, it triggers the production of second messengers like cAMP, which amplify the signal and initiate a cascade of biochemical reactions within the cell, affecting processes like metabolism and gene expression.

Adenylate Cyclase

Adenylate cyclase is an enzyme that catalyzes the conversion of ATP to cyclic AMP. It is often activated by G-protein coupled receptors (GPCRs) upon ligand binding. The activity of adenylate cyclase is crucial for the generation of cAMP, which then acts as a second messenger to propagate the signal within the cell, influencing various physiological responses.