C-peptide of human insulin is

1. a part of mature insulin molecule
2. responsible for the formation of disulphide bridges
3. removed during maturation of pro-insulin to insulin
4. responsible for its biological activity

(3) The connecting peptide or C-peptide is a short protein containing 31 amino acids. It connects the A and B chain of proinsulin molecule. After the processing of proinsulin molecule, C-peptide is removed leaving behind A and B chains which bound together by disulphide bonds to constitute a insulin molecule.