Write a short note on the Mechanism of Hormone Action

Amino acid-derived hormones (water solubles) cannot enter through plasma membrane and function as first messenger. The steps of action are –

(i) Hormone binds to receptor protein present in plasma membrane.

(ii) Receptor protein activates G-protein present inside the cell.

(iii) G-protein activates adenyl cyclase of plasma membrane.

(iv) Adenyl cyclase converts ATP to cyclic AMP called second messenger.

(v) cAMP binds to protein kinases which in turn bind to specific site of DNA and cause gene expression.

Steroid hormones, being lipid soluble enter through plasma membrane and bind to receptor protein to form a complex. The complex binds to specific site of DNA and stimulates specific gene expression.