1) Formation of Preproinsulin:
Insulin synthesis begins with preproinsulin (110 amino acids), synthesized in the rough endoplasmic reticulum.
2) Conversion to Proinsulin:
Preproinsulin is processed in the Golgi apparatus to form proinsulin, an inactive precursor.
3) Folding and Bond Formation:
Proinsulin folds to form three disulfide bonds, linking the A-chain and B-chain.
4) Packaging into Vesicles:
Folded proinsulin is packaged into secretory vesicles for further processing.
5) Cleavage by Enzymes:
Enzymes (Proprotein Convertase 1/3 and Proprotein Convertase 2) cleave the C-peptide from proinsulin.
6) Final Processing:
Carboxypeptidase E removes terminal amino acids, yielding active insulin.
7) Active Insulin:
Active insulin consists of:
Chain A: 21 amino acids.
Chain B: 30 amino acids.
Chains are connected by two disulfide bonds.
8) Secretion:
Active insulin is secreted into the bloodstream to regulate blood sugar and metabolic processes.
Structure of Insulin