Question

Why second-messenger systems are required for peptide hormones?

Answer 1

1. The hormones which are derivatives of proteins, amino acids or polypeptides are called peptide hormones.
2. These hormones being insoluble in lipids cannot enter the target cell.
3. They act as primary messengers on the surface of the target cell and bind to the receptors present on the outer surface of the plasma membrane to form a hormone-receptor complex.
4. The enzyme Adenylyl cyclase is activated by this complex.
5. On the inner surface of the plasma membrane, Adenylyl cyclase catalyzes the conversion of ATP to cyclic AMP.
6.  Cyclic AMP (cAMP) acts as the secondary messenger which delivers the information to the inside of the target cell.
7. This activates an appropriate cellular enzyme system by means of cascade effect.
8. cAMP is short-lived and rapidly degraded by cAMP phosphodiesterase.
9. Thus, peptide hormones are quick acting hormones and produce an immediate effect through cAMP.