Second Messengers

  • Definition: Small intracellular molecules that relay signals from cell surface receptors to target molecules inside the cell.

  • Function: Amplify and distribute the signal from the first messenger (e.g., hormone, neurotransmitter).

Examples & Sources:

  1. cAMP – Produced from ATP by adenylate cyclase after β-adrenergic receptor activation.

  2. IP₃ (Inositol 1,4,5-trisphosphate) – Produced from PIP₂ by phospholipase C; releases Ca²⁺ from endoplasmic reticulum.

  3. DAG (Diacylglycerol) – Activates protein kinase C.

  4. Ca²⁺ – Binds calmodulin, activates calcium-dependent kinases.

  5. cGMP – Produced from GTP by guanylate cyclase; mediates effects of nitric oxide.

Memory tip: “cAMP, cGMP, Ca²⁺, DAG, IP₃” — the big five second messengers.

✅ 2-mark condensed version:
"Second messengers are small intracellular molecules (e.g., cAMP, cGMP, Ca²⁺, IP₃, DAG) that transmit and amplify signals from the first messenger (like hormones) to intracellular targets."

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