How Bacteria Make Human Insulin: The Technique That Will Amaze You

One of the most surprising things I tell my Honors Biology students is this: the insulin that millions of people with diabetes inject every day is made by bacteria. Not extracted from humans, not synthesized from scratch in a lab, but produced by living bacterial cells following human genetic instructions. This is an exciting and fascinating use of biotechnology, one that touches the lives of so many people.

The ability to do this comes down to one remarkable fact. All living things use the same genetic code. A bacterium reads DNA the same way a human cell does, which means if you place a human gene inside a bacterial cell, that bacterium will follow the human instructions and produce the human protein. It has no way of knowing the instructions came from a different species. It simply reads the code and in this case produces the human insulin.

That idea is fascinating, but here is what your Honors Biology teacher may test you on: the step-by-step technique that actually makes it happen.

The Technique: How the Insulin Gene Gets Into Bacteria

This process uses restriction enzymes and a small circular piece of bacterial DNA called a plasmid. For the full explanation of how restriction enzymes work, see the restriction enzymes article in this series. Here is how the complete technique works:

1. Scientists identify the human gene responsible for producing insulin and locate it within human DNA.

2. Restriction enzymes cut the insulin gene out of human DNA at specific locations, leaving sticky ends — short single-stranded overhangs ready to bond with matching DNA.

3. The same restriction enzymes cut open a bacterial plasmid, creating matching sticky ends.

4. The human insulin gene and the open plasmid are combined. The sticky ends bond together temporarily through base pairing.

5. DNA ligase then permanently seals the connection, creating recombinant DNA — a bacterial plasmid that now carries the human insulin gene.

6. The recombinant plasmid is inserted into a bacterial cell.

7. As the bacteria reproduce, every new cell carries the recombinant plasmid and produces human insulin by following the inserted human gene's instructions.

8. Large populations of bacteria are grown that produce the insulin, which can then be collected, purified, and packaged for medical use.

Why This Matters Beyond the Test

Before this technology existed, insulin for diabetes treatment came from pigs and cows, which caused immune reactions in some patients. Bacteria-produced human insulin is identical to what the human body makes naturally, making it safer and more effective. Bacteria are also ideal for this process because they reproduce rapidly, allowing the growth of massive quantities of insulin-producing bacterial cells in a short time.

Insulin production is one of the most commonly used examples of beneficial biotechnology in Honors Biology, but how deeply your teacher tests this topic and which details they emphasize will vary. Check your class materials and study guides to understand their focus.

I offer one-on-one online tutoring tailored to your specific Honors Biology curriculum if you want to work through this material with someone focused on exactly what your teacher is covering.

READ MORE

• Restriction Enzymes

• RNA Processing

• Central Dogma