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A short class with Sarah and her students. The other ways are under More.
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Insulin lowers blood glucose after a meal. What happens to someone with type 1 diabetes?
Their pancreas doesn't make enough insulin, so their blood glucose stays too high.
Right: their immune system has destroyed the beta cells that make it, so they need insulin every day. Where do you think that insulin came from in the past?
From animals?
Yes, from the pancreases of pigs and cattle. Pig insulin differs from ours by one amino acid, cow insulin by three.
So some people's bodies might react to it, and the supply depends on slaughterhouses.
Exactly the problems genetic engineering set out to solve.
Step one is getting the gene. Why can't we just cut the insulin gene out of a human chromosome and give it to a bacterium?
Because human genes have introns, and bacteria can't remove them.
Good. So scientists copy the gene from insulin mRNA using reverse transcriptase, or build it artificially. What next?
Cut the gene and a plasmid with the same restriction enzyme, so their sticky ends match.
And DNA ligase seals them into a recombinant plasmid. Then?
Transformation: the bacteria take up the plasmid, and an antibiotic-resistance marker lets us select the ones that did.
Perfect: isolate, cut, insert, transform, select. Then grow them in fermenters.
If one bacterium divides every 20 minutes, how many cells are there after one hour?
Three divisions, so two times two times two: eight.
And after ten hours it is 30 divisions, about a billion cells. That is why bacteria make such good factories. What are the benefits for patients?
The insulin is identical to human insulin, so fewer reactions, and there is always enough.
Good. Are there any ethical questions?
We have to keep the modified bacteria contained, and the medicine has to be affordable for everyone who needs it.
Exactly. A great scientific success still raises questions about safety and fairness.
People with type 1 diabetes cannot make insulin and must take it every day.
Bacteria cannot remove introns, so they are given cDNA or an artificial gene.
The same restriction enzyme cuts the gene and the plasmid, and DNA ligase joins them.
A marker gene, such as antibiotic resistance, identifies the bacteria that took up the plasmid.
Fast-dividing bacteria in fermenters make large amounts of insulin identical to human insulin.
Before 1982, a diabetic patient's insulin came from pig or cattle pancreases; today it is usually made by genetically engineered bacteria or yeast.
In 1978, human insulin was first made in E. coli using artificial genes for the A and B chains, which were produced separately and then joined.
A single E. coli cell that divides every 20 minutes becomes 2³⁰, or about 1.07 billion cells, after 10 hours in ideal conditions.
Copy the gene, cut it clean, seal it in a ring, let bacteria sing.
A recipe for insulin is written out cleanly, without the doodles, slipped into a tiny ring binder, and handed to a bakery of bacteria. Only the bakers who received the binder survive the inspection, and they bake insulin around the clock.
Ivy Cuts Into Tasty Strawberries - Isolate, Cut, Insert, Transform, Select.
P.L.A.S.M.I.D. - Pick the gene, Ligase seals, Add to bacteria, Select with antibiotic, Multiply in fermenters, Isolate insulin, Deliver to patients.
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Which organism was first used to make human insulin?
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Why must the insulin gene given to bacteria be intron-free?
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Why use the same restriction enzyme on the gene and the plasmid?
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How are transformed bacteria selected?
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One advantage of engineered human insulin over animal insulin
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A hormone made by the beta cells of the pancreas that lowers blood glucose.
A condition in which the immune system destroys the insulin-making cells, so the person must take insulin daily.
A small circle of DNA in bacteria, used as a vector to carry a new gene into a cell.
An enzyme that cuts DNA at a specific base sequence, often leaving sticky ends.
An enzyme that joins pieces of DNA by sealing their sugar-phosphate backbones.
A plasmid that contains DNA from another organism, such as the human insulin gene.
DNA copied from mRNA by reverse transcriptase, which has no introns.
A large controlled vessel in which microorganisms are grown to make a product.
Human insulin for people with diabetes is made by genetically engineered bacteria: the human insulin gene is placed in a plasmid, put into E. coli, and the bacteria are grown in huge numbers to produce the hormone.
This lesson follows one of the first and most important uses of genetic engineering from start to finish. It explains why people with diabetes need insulin and how it was obtained from animals before 1982, then applies each step of genetic engineering to insulin: obtaining a gene the bacteria can use, cutting it and a plasmid with the same restriction enzyme, joining them with DNA ligase, transforming E. coli, selecting the bacteria that took up the plasmid, and growing them in fermenters. It ends with the benefits of the method and the questions it raises.
This lesson follows the steps of genetic engineering through one real and life-saving example: the production of human insulin by bacteria.
Insulin is a hormone made by the beta cells of the islets of Langerhans in the pancreas. After a meal it lowers the glucose level in the blood by helping cells take in glucose and by causing the liver and muscles to store glucose as glycogen. In type 1 diabetes the body's immune system destroys the beta cells, so little or no insulin is made and the person needs insulin every day for life.
Insulin was first used to treat a patient in 1922. For about sixty years after that, it was extracted from the pancreases of pigs and cattle collected from slaughterhouses. Animal insulin works, but it is not identical to ours: pig insulin differs from human insulin by one amino acid and cow insulin by three. Supplies depended on the meat industry, and some patients reacted to the animal protein.
The selected bacteria are grown in large steel fermenters (bioreactors) in which temperature, pH, oxygen and nutrients are carefully controlled. Under ideal conditions E. coli can divide about every 20 minutes, so numbers grow very quickly: one cell dividing every 20 minutes for 10 hours goes through 30 divisions and becomes 2³⁰, about 1.07 billion cells. The insulin is then extracted from the cells, purified, its chains joined correctly, and tested before it is made into medicine. Today some manufacturers use yeast cells instead of bacteria, but the principle is the same.
Genetically engineered human insulin was approved for patients in 1982, the first medicine made by genetic engineering to reach the market. Its advantages are that it is identical to the insulin the body makes, so it causes fewer immune reactions; it can be made in almost unlimited amounts; its quality is consistent; and it does not depend on animals, which also matters to people who avoid pig or cow products. At the same time, it raises bioethical questions about working with genetically modified organisms safely (they are kept contained inside fermenters) and about whether everyone who needs insulin can afford it.