Second messengers — cAMP and cGMP are generated from which nucleotides, and by which cyclase enzymes?

Introduction:
Cyclic nucleotides are universal second messengers in cell signaling. This question checks whether you know the biochemical origins of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) and the specific cyclase enzymes that synthesize them.

Given Data / Assumptions:

• cAMP derives from adenosine triphosphate (ATP).
• cGMP derives from guanosine triphosphate (GTP).
• Dedicated cyclase enzymes catalyze ring closure and pyrophosphate release.

Concept / Approach:
Adenylyl (adenylate) cyclase converts ATP to cAMP; guanylyl (guanylate) cyclase converts GTP to cGMP. These enzymes are activated by distinct upstream signals: many G protein coupled receptors regulate adenylyl cyclase via Gs or Gi, while guanylyl cyclases can be membrane bound receptors (e.g., natriuretic peptide receptors) or soluble enzymes stimulated by nitric oxide.

Step-by-Step Solution:

Verification / Alternative check:
Pharmacologic tools (e.g., forskolin) stimulate adenylyl cyclase to increase cAMP, while nitric oxide donors elevate cGMP via soluble guanylyl cyclase. These classic manipulations confirm the enzyme–substrate pairings in living cells.

Why Other Options Are Wrong:

• GTP with adenylyl cyclase and ATP with guanylyl cyclase: swaps substrates and enzymes.
• ATP with guanylyl cyclase and GTP with adenylyl cyclase: mismatched enzyme specificity.
• CTP/UTP: these are not standard cyclic second messengers in this context.
• None of the above: incorrect because one option matches canonical biochemistry.

Common Pitfalls:
Confusing guanylyl cyclase with adenylyl cyclase due to similar names. Remember: cAMP comes from ATP via adenylyl cyclase; cGMP comes from GTP via guanylyl cyclase.

Final Answer:
ATP and GTP by the actions of adenylate cyclase and guanylate cyclase respectively.