Q.33 Cyclic AMP (cAMP) acts as a second messenger for which of the following primary signaling
molecule(s)?
(A) Retinoic acid (B) Prostaglandins
(C) Cortisol (D) Epinephrine
Cyclic AMP (cAMP) serves as a key second messenger in cellular signaling, particularly for epinephrine. The correct answer to the query is (D) Epinephrine.
Correct Answer
Epinephrine binds to G-protein-coupled receptors (GPCRs), activating adenylyl cyclase to produce cAMP from ATP. This cAMP then activates protein kinase A (PKA), amplifying the fight-or-flight response through glycogenolysis and other metabolic changes.
Option Analysis
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(A) Retinoic acid: Acts primarily through nuclear receptors (RARs/RXRs) to regulate gene transcription, independent of cAMP as a second messenger; any cAMP involvement is secondary or context-specific, not primary.
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(B) Prostaglandins: Signal via GPCRs but typically elevate intracellular calcium or activate PKC pathways; cAMP mediation occurs in some cases but is not the primary mechanism.
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(C) Cortisol: A steroid hormone that diffuses across membranes to bind glucocorticoid receptors, directly influencing gene expression without second messengers like cAMP.
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(D) Epinephrine: Correct; uses β-adrenergic receptors to stimulate cAMP production as the core second messenger for rapid metabolic responses.
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cAMP Signaling Pathway
cAMP binds regulatory subunits of PKA, releasing catalytic subunits that phosphorylate targets like phosphorylase kinase. This pathway exemplifies GPCR-mediated signaling in endocrinology and biochemistry.
