Question

During the processing of proinsulin into mature insulin
A. C-peptide is added to proinsulin
B. C-peptide is removed from proinsulin
C. B-peptide is added to proinsulin
D. B-peptide is removed from proinsulin

Answer 1

Proinsulin is a single polypeptide chain composed of the B and A subunits of insulin joined by the C-peptide region.Proinsulin is converted to insulin during the maturation of secretory vesicles by the action of enzymes.

Complete answer:
Option A- C- peptide is added to proinsulin
C-peptide is a connecting peptide, it is a short 31-amino acid polypeptide that connects insulin's A-chain to its B-chain in the proinsulin molecule.
Option B- C-peptide is removed from proinsulin
Insulin is used for diabetes which is synthesized by a pro hormone in humans.The prohormone needs to be processed to become a fully mature and functional hormone as it contains an extra stretch called C- peptide which is not present in the mature insulin.
Option C - B-peptide is added to proinsulin
Is also known as B-type natriuretic peptide , it is mainly seen diabetes mellitus patients now days most often.B chains are linked together by two disulfide bonds and a additional disulfide is formed within the A chain
Option D- B-peptide is removed to proinsulin
This option is not correct. As B- peptide subunit is important for insulin structure.

Hence, the correct answer is option (B).

Note: Proinsulin is the prohormone precursor to insulin made in the beta cells of the islets of langerhans which is specialised regions of the pancreas.In humans, proinsulin is encoded by the INS gene.