Core second messengers – Which list correctly identifies major intracellular second messengers used in many signal transduction pathways?

Introduction:
Second messengers translate receptor activation into intracellular responses by regulating kinases, channels, and gene transcription. Recognizing the canonical second messengers is fundamental to understanding diverse pathways across cell types.

Given Data / Assumptions:

• cAMP is generated by adenylyl cyclase downstream of GPCRs (Gs).
• cGMP is generated by guanylyl cyclase (soluble or membrane-bound).
• DAG arises from PIP2 cleavage by PLC and remains in the membrane.

Concept / Approach:
cAMP activates protein kinase A and other effectors; cGMP activates protein kinase G and certain ion channels; DAG activates conventional and novel PKC isoforms (often with Ca2+ and phosphatidylserine). Together with IP3 and Ca2+, these messengers form a core toolkit for intracellular signaling across many receptors.

Step-by-Step Solution:

Verification / Alternative check:
Pharmacologic modulators (e.g., PDE inhibitors, PKC activators like phorbol esters) alter cellular responses by changing levels or actions of these messengers, underscoring their central role.

Why Other Options Are Wrong:

• Each individual choice alone is incomplete; the question asks which list correctly identifies the major messengers among the options.
• Insulin is an extracellular hormone (first messenger), not a second messenger.

Common Pitfalls:
Confusing extracellular ligands with intracellular messengers or overlooking DAG because it is membrane-bound rather than freely diffusible.

Final Answer:
All of these