As we have studied in:
Mode of Protein Hormone Action through Extracellular Receptors:
- Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues only.
- The hormone-receptor complex induces the release of GDP from the G protein.
- The α- subunit bearing GTP separates from the combined β and ? subunits. The β and ? subunits do not separate from each other.
- The activated β and γ subunits of G protein activate adenyl cyclase.
- The activated adenyl cyclase catalyses the formation of cyclic adenosine monophosphate (cAMP) from ATP.
- The hormone is called the first messenger and cAMP is termed the second messenger.
- Amplification of the signal through a cascade effect.
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cAMP is the secondary messenger in peptide hormone action
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