Insulin From Bacteria: How Scientists Taught Microbes to Save Lives

In 1921, a young doctor named Frederick Banting discovered insulin — the hormone that lets our bodies use sugar for energy. Within a year, a 14-year-old boy named Leonard Thompson was dying of diabetes. Doctors gave him the first insulin injection ever given to a human, and he survived. For the next 60 years, doctors extracted insulin from the pancreases of pigs and cows. Then in 1982, something revolutionary happened: bacteria made the insulin instead. It was the first medicine ever created through genetic engineering, and it changed medicine forever.

You will learn why people with type 1 diabetes need insulin every single day to stay alive. You will discover what DNA, genes, and plasmids are and how scientists use them like a biological copy-and-paste tool. You will trace the step-by-step process of how scientists programmed bacteria to produce human insulin. And you will understand why synthetic insulin is safer and more reliable than the animal-sourced kind it replaced.

Your body runs on glucose, a type of sugar that comes from the food you eat. But glucose cannot get inside your cells without help — it needs a key to unlock the door. Insulin is that key. Your pancreas normally makes insulin automatically after every meal. People with type 1 diabetes have an immune system that accidentally attacks and destroys the cells in the pancreas that make insulin. Without daily insulin injections, their blood sugar rises to dangerous levels, damaging the eyes, kidneys, and nerves — and eventually causing death. About 8.4 million people in the United States inject insulin every day. Without it, type 1 diabetes is fatal within weeks.

From the 1920s to the early 1980s, insulin was extracted from the pancreases of pigs and cows at meat-processing plants. It worked because pig insulin is almost identical to human insulin — differing by only one amino acid out of 51. But there were real problems. Some patients had allergic reactions to the animal proteins. The supply was never reliable — millions of animal pancreases were needed each year just to treat US patients. And as diabetes rates grew worldwide, scientists worried the animal supply simply could not keep up. They needed a better way to make unlimited quantities of a medicine that matched human insulin exactly.

Bacteria are single-celled organisms that divide and multiply very rapidly — one can become a trillion in less than a day. They follow instructions written in their DNA. The big idea: what if scientists could copy the human DNA instruction for making insulin and insert that copy into bacteria? The bacteria would then follow those instructions and produce human insulin by the billions. The tool scientists used is called recombinant DNA technology. Here are the steps: 1. Scientists found the exact stretch of human DNA that codes for insulin — a sequence of 153 DNA letters. 2. They used molecular scissors called restriction enzymes to cut that section out. 3. Bacteria contain small circular loops of DNA called plasmids, separate from their main chromosome. Scientists cut open a plasmid and inserted the human insulin gene into it. 4. The modified plasmid was put back into a harmless strain of E. coli bacteria. The bacteria now carried the human insulin blueprint. 5. The bacteria multiplied in huge fermentation tanks — trillions of bacteria, all producing human insulin. 6. Scientists harvested, purified, and packaged the insulin for patients.

The insulin made this way launched in 1982 under the brand name Humulin. It is chemically identical to the insulin your own pancreas would make — the exact same protein, folded the exact same way — so patients get far fewer allergic reactions. It can be produced in unlimited quantities as long as bacteria are fed and kept warm in a tank. And it is more consistent batch to batch than anything extracted from animals. Today virtually all insulin used worldwide is produced this way. The same recombinant DNA approach now makes dozens of other medicines: growth hormone, blood-clotting factors for hemophilia, and even some COVID vaccines.