The chains of mature insulin are joined together by:

The correct answer is Option (3) → Disulfide bonds

Mature insulin is made of two short polypeptide chains, chain A and chain B. In the body it is first made as one long chain, pro-insulin. A middle piece (the C peptide) is cut off, and the two remaining chains stay joined.

(1) Glycosidic bonds — Incorrect. These join sugar units into carbohydrates such as starch. Insulin is a protein.

(2) Hydrogen bonds — Incorrect. They give shape within a protein and hold base pairs together in DNA. They are weak and are not the bridges that tie chain A to chain B.

(3) Disulfide bonds — Correct. Sulphur-containing amino acids form disulphide bridges. These bridges link chain A with chain B.

(4) Phosphodiester bonds — Incorrect. These join nucleotides in DNA and RNA.

Figure 10.3 Maturation of pro-insulin into insulin (simplified)

Note: A similar question was also asked in CUET (UG) 2023 on 31-05-2023 (Slot 3).

NCERT Extract:
Genetically Engineered Insulin – “… Chains A and B were produced separately, extracted and combined by creating disulfide bonds to form human insulin.”