How is recombinant human insulin produced using bacteria?

• A. Bacteria naturally produce human insulin without genetic modification.
• B. The human insulin gene is inserted into a plasmid, but the bacteria do not express insulin.
• C. The human insulin gene is inserted into a plasmid, transformed into bacteria, which express insulin, harvested and purified.
• D. The insulin gene is inserted into bacteria, but the protein is never harvested.

Answer: (C)

Producing a human protein in bacteria relies on recombinant DNA to get the cell to make the human product. The human insulin gene is placed into a plasmid vector that has a promoter and other regulatory elements, then this plasmid is introduced into bacteria. Under control of those elements, the bacteria synthesize insulin as they grow. The insulin is then collected from the culture and purified to separate it from bacterial proteins and other components, often after processing to reach the active, correctly folded form. This sequence—insert gene into plasmid, transform bacteria, bacteria express insulin, harvest and purify—is why this approach works. The other statements would not allow production to be recovered or would claim insulin is made without modification, which isn’t correct.