CBSE · Class 12 · Biology · Biotechnology and its ApplicationsExplain the production of genetically engineered human insulin (Humulin). Discuss the challenges faced initially, how Eli Lilly overcame them using recombinant DNA technology, and why this method is superior to animal-extracted insulin.

Introduction to Human Insulin and Recombinant Production\nInsulin is a vital peptide hormone produced by the pancreas that regulates blood glucose levels. Patients suffering from Type-I diabetes mellitus require regular insulin injections. Historically, insulin was extracted from the pancreas of slaughtered cattle and pigs. However, animal insulin caused allergic reactions and other complications in some patients due to structural differences. This prompted the development of recombinant human insulin, commercially known as Humulin.

Structure of Natural Human Insulin

• Natural human insulin consists of 51 amino acids arranged in two polypeptide chains:
  • Chain A: Contains 21 amino acids.
  • Chain B: Contains 30 amino acids.
• These two chains are interconnected by disulfide bonds.
• In humans, insulin is synthesized as a pro-hormone containing an extra stretch called the C-peptide. During maturation, the C-peptide is removed, leaving only chains A and B.

Initial Challenges in Recombinant Production\nThe primary challenge for scientists was synthesizing the active form of human insulin directly inside bacterial hosts because prokaryotes cannot process pro-hormones or remove C-peptides. Therefore, assembling chains A and B separately was essential.

Eli Lilly and Company Breakthrough (1983)

• In 1983, an American pharmaceutical company, Eli Lilly, successfully prepared two DNA sequences corresponding to A and B chains of human insulin.
• Gene Insertion: They introduced these isolated human insulin genes into plasmids of Escherichia coli bacteria.
• Culturing: The recombinant E. coli strains were cultured in large fermentation tanks, where they independently synthesized human insulin Chain A and Chain B.
• Extraction and Joining: Chains A and B were extracted separately from the bacterial cultures. Finally, the two chains were combined and linked together by establishing artificial disulfide bonds in vitro, successfully yielding fully functional human recombinant insulin (Humulin).

Advantages of Humulin Over Animal-Extracted Insulin

• No Immune Reactions: Since Humulin is identical to natural human insulin, it does not provoke immune responses or allergic reactions, unlike animal-derived insulin.
• Abundant Supply: Recombinant production allows limitless mass production through fermentation, overcoming the shortage of animal pancreas sources.
• Purity and Safety: Microbial fermentation eliminates the risk of transmitting animal pathogens, viruses, or contaminants.