By the end of this lesson
- Describe the steps in producing human insulin from GM bacteria.
- Explain why a fermenter is used.
- Evaluate the advantages of GM insulin.
BIG QUESTION
How can bacteria make a human hormone?
Bacteria given the human insulin gene read it with the same genetic code and make human insulin.
Making the GM bacteria
The human insulin gene is cut from human DNA with a restriction enzymeAn enzyme that cuts DNA at a specific base sequence (its recognition site), often leaving sticky ends.. A plasmidA small ring of DNA in a bacterial cell, separate from the main chromosome, used as a vector in genetic engineering. is cut with the same enzyme, giving matching sticky ends.
The gene is inserted into the plasmid and sealed with DNA ligaseAn enzyme that joins pieces of DNA together, such as a gene into a plasmid.. The recombinant plasmids are mixed with bacteria, and bacteria that take them up are identified.
Growing in a fermenter
GM bacteria reproduce rapidly in a fermenterA large vessel in which microorganisms are grown under controlled conditions to make a useful product., copying the plasmid each time they divide. Each bacterium uses the gene to make human insulin.
Conditions are controlled: aseptic, with nutrients, oxygen, suitable pH and optimum temperature, so the bacteria grow quickly and produce large amounts of insulin.
Extracting and evaluating
Insulin is extracted from the culture and purified. The bacteria make insulin identical to human insulin.
Compared with insulin extracted from pigs or cattle, it can be made in large, consistent quantities and avoids some ethical and religious objections. Some patients may still prefer animal insulin.
Sources of insulin
GM bacteria changed how insulin is supplied.
| Feature | Animal insulin | GM bacterial insulin |
|---|---|---|
| Structure | Slightly different from human. | Identical to human insulin. |
| Supply | Limited by animals slaughtered. | Large amounts from fermenters. |
| Ethical issues | Some religious or animal-welfare objections. | Fewer, though some object to GM. |
Language that earns precision
- insulin
- A hormone that lowers blood glucose concentration.
- recombinant plasmid
- A plasmid containing an inserted gene.
- fermenter
- A vessel for growing microorganisms in controlled conditions.
- purification
- Separating the wanted product from other substances.
Common misconceptions
Claim: The bacteria are injected into patients.
Correction: Insulin is extracted and purified; patients receive the hormone, not bacteria.
Claim: Bacteria make insulin naturally.
Correction: They make it only after receiving the human insulin gene.
Claim: Each bacterium needs a new plasmid inserted.
Correction: Plasmids are copied when bacteria divide.
Match the answer to the command word
Cut gene, cut plasmid (same enzyme), insert, ligase, into bacteria, grow in fermenter, extract.
Link the fermenter conditions to rapid reproduction of bacteria and large-scale production.
Recall, apply, then justify
Describe how genetically modified bacteria are produced that can make human insulin.
Hint
Enzymes and vector.
Suggested marking points
- Restriction enzyme cuts the insulin gene from human DNA.
- The same restriction enzyme cuts the plasmid.
- Ligase joins the gene into the plasmid.
- The recombinant plasmid is taken up by bacteria.
Explain why GM bacteria are grown in a fermenter.
Hint
Conditions and quantity.
Suggested marking points
- Conditions are controlled for optimum growth (temperature, pH, nutrients, oxygen, aseptic).
- Bacteria reproduce rapidly so large amounts of insulin are produced.
Evaluate the production of human insulin using genetically modified bacteria compared with extracting insulin from animals.
Planning hint
Structure, quantity, cost, ethics.
What a strong design includes
- GM insulin is identical to human insulin.
- Large amounts can be produced quickly and continuously.
- Supply does not depend on slaughtering animals.
- Fewer religious or ethical objections linked to animal sources.
- Setting up GM production and fermenters is expensive.
- Some people object to GM organisms or some patients respond better to animal insulin.