NEET 2025 Botany Question 116 Solution

Insulin for diabetes was traditionally extracted from pancreas of slaughtered cattle and pigs, causing severe allergic reactions in some patients:

• • Human insulin is synthesized as a pro-hormone containing an extra C-peptide which is removed during maturation.
• • The major challenge for production of insulin using rDNA techniques was getting insulin assembled into a mature form.

The breakthrough approach devised by Eli Lilly:

• • Synthesized two separate DNA oligonucleotides encoding human chain A (21 amino acids) and chain B (30 amino acids).
• • Inserted these sequences into expression plasmids downstream of the $\beta$-galactosidase promoter.
• • Transformed these plasmids into *Escherichia coli* (*E. coli*), which is a bacterium.
• • Chains A and B were extracted from the bacterial cultures and linked in vitro by forming disulfide bonds to yield active mature human insulin.

*E. coli* belongs to Domain Bacteria (Eubacteria). Hence, the organism class used is a Bacterium.