Gene technology: insulin, gene therapy and GM crops – Genetics and Gene Technology (Senior 3 Biology) | Ganzaa

Genetics and Gene Technology

Lessons

Senior 3 · Biology

Genetics and Gene Technology

5 lessons

Lesson 5 of 5

Gene technology: insulin, gene therapy and GM crops

25 min

A human hormone made by bacteria

In Unit 10 you saw that the hormone insulin lowers blood glucose, and that people with type 1 diabetes cannot make enough of it. They need insulin injections for life. From the 1920s, insulin for injection was extracted from the pancreases of slaughtered cattle and pigs. Animal insulin works, but it is not identical to human insulin, some patients reacted to it, and the supply depended on how many animals were slaughtered.

In 1982 a new kind of insulin was approved for patients: human insulin, made by bacteria. The human gene for insulin had been put into the bacteria, and they followed its instructions. This lesson explains how genes can be moved from one organism to another, and asks when it is wise to do so.

Definition

Genetic engineering (genetic modification): changing the DNA of an organism, usually by inserting a gene from another organism.

Genetically modified organism (GMO): an organism whose DNA has been changed by genetic engineering. One that carries a gene from another species is called transgenic.

Restriction enzyme: an enzyme that cuts DNA at a particular base sequence, leaving short single-stranded "sticky ends".

DNA ligase: an enzyme that joins pieces of DNA together.

Plasmid: a small ring of DNA found in bacteria, separate from the main bacterial chromosome. A plasmid used to carry a gene into a cell is a vector.

Recombinant DNA: DNA made by joining DNA from two different sources, such as a plasmid with a human gene in it.

How bacteria are made to produce human insulin

Figure 1. Making human insulin with genetically engineered bacteria.

The human insulin gene is cut out of human DNA with a restriction enzyme.
A bacterial plasmid is cut open with the same restriction enzyme, so its sticky ends match the ends of the gene.
The gene and the opened plasmid are mixed with DNA ligase, which joins them: this is a recombinant plasmid.
Bacteria take up the recombinant plasmids.
The bacteria are grown in a large fermenter with food, warmth and oxygen. Each time a bacterium divides, the plasmid and the insulin gene are copied.
The bacteria make human insulin, which is extracted, purified and packed for injection.

The same method is used for other human proteins, such as human growth hormone, and for some vaccines.

Worked example

Worked example 1: why use bacteria? In good conditions a bacterium can divide every 20 minutes. Starting from one genetically engineered bacterium, how many could there be after 10 hours? Use your answer to explain why bacteria are used.

Solution

Number of divisions in 10 hours: $\frac{10 \times 60}{20} = 30$ .
Each division doubles the number: $2^{30} = 1\,073\,741\,824 \approx 1.07 \times 10^{9}$ bacteria.
Every one carries the insulin gene. So bacteria give a very large amount of product quickly and cheaply, from cells that are easy to grow in a fermenter.

Human insulin made this way is identical to the hormone of the human body, and its supply does not depend on animals.

Gene therapy

Some genetic disorders are caused by a single faulty allele. In gene therapy, doctors add a working copy of the gene to the patient's cells, or correct the faulty gene. A harmless virus is often used as the vector to carry the gene into the cells; in other methods, cells are taken from the patient, treated in a laboratory and returned.

Gene therapy is new, difficult and costly, and is available in only a few hospitals in the world. Some treatments have worked well: in 2023, for example, the first gene therapies for sickle-cell disease were approved in the United Kingdom and the United States, using the patient's own treated bone-marrow cells. The treatment changes only body (somatic) cells, such as blood or bone-marrow cells. It does not change the patient's gametes, so it is not passed on to the patient's children.

Definition

Gene therapy: the treatment of a genetic disorder by adding a working copy of a gene to a patient's cells, or by correcting the faulty gene.

Somatic cell: any body cell other than a gamete or a cell that makes gametes. Changes to somatic cells are not inherited.

Genetically modified crops

Plants can be genetically modified too. Three well-known kinds:

GM crop	Gene added	Effect
Bt maize, Bt cotton	a gene from the soil bacterium Bacillus thuringiensis	the plant makes a protein that kills certain caterpillars that eat it, so less insecticide is sprayed
Golden Rice	genes that make beta-carotene in the grain	the body turns beta-carotene into vitamin A; meant to reduce vitamin A deficiency
Late-blight-resistant potato	resistance genes from wild relatives of the potato	the plant resists late blight, a disease that rots leaves and tubers

In Rwanda

Late blight is a serious disease of potatoes, and ordinary varieties usually need repeated fungicide sprays. The Rwanda Agriculture and Animal Resources Development Board (RAB) reports that the Rwanda Environment Management Authority (REMA) approved confined and open field trials of genetically modified Victoria and Ndamira (Shangi) potatoes over ten years. On 11 June 2026, at a RAB field day at its Musanze station, these potatoes showed strong resistance to late blight in open fields. RAB notes that they are not yet released to farmers: further regulatory steps must be completed first.

Benefits and drawbacks of GMOs

Possible benefits	Possible drawbacks and concerns
Higher, more reliable yields, because crops resist pests, diseases or drought	Pollen may carry the added gene to wild relatives of the crop
Less insecticide or fungicide sprayed, which saves money and protects farm workers and wildlife	Pests and pathogens may evolve resistance if the same GM crop is grown everywhere
Better nutrition, such as vitamin A in Golden Rice	GM seed can be costly, and patents may make farmers depend on a few seed companies
Medicines such as human insulin, made cheaply and safely	Growing only a few varieties reduces the genetic diversity of crops
A gene can be added in a few years, much faster than by breeding	Each product needs testing (for example for allergens) and public trust; some markets refuse GM food

The World Health Organization states that the GM foods on the international market have passed safety assessments and are not likely to present risks to human health, and that each new GM food should be assessed case by case. So the question is rarely "Are GMOs good or bad?" It is "Is this GM product, in this place, better than the alternatives?"

Worked example

Worked example 2: evaluating a GM crop. A potato cooperative in a cool, wet highland district loses part of its crop to late blight every rainy season and sprays fungicide many times. Suppose a late-blight-resistant GM potato is approved. Should the cooperative grow it?

A strong answer weighs both sides.

For: yields would be more reliable in wet seasons; fewer fungicide sprays would cut costs and exposure of workers to chemicals; less fungicide would reach streams.
Against, or cautions: the seed may cost more and must come from approved sources; late blight could, in time, overcome the resistance if no other control is used; buyers' acceptance must be checked; growing only one or two varieties lowers diversity.
Conclusion: it is a good choice if the variety is approved by the regulators, seed is affordable, and farmers keep good practice (crop rotation, clean seed, some other varieties) so the resistance lasts.

Warning

Avoid both extremes. "GM food is poison" is not supported by the evidence on approved products. "GMOs have no risks" is also wrong: each one has to be tested and regulated. And genetic engineering is not the same as selective breeding (Unit 14): breeding chooses among genes that a species already has, while genetic engineering can add a gene from a completely different species.

Genetic engineering, from FuseSchool. Watch for the roles of the restriction enzyme, DNA ligase and the plasmid vector, and how they match Figure 1.

Tip

Cut, paste, copy. Restriction enzyme = scissors (cut); ligase = glue (paste); bacteria in a fermenter = photocopier (copy). In exam answers use the proper names.

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Practice: gene technology

Define (a) genetic engineering, (b) a genetically modified organism.
Name the enzyme that (a) cuts DNA at a particular base sequence, (b) joins two pieces of DNA.
Put these steps in order: bacteria multiply in a fermenter; a plasmid is cut open; insulin is purified; the insulin gene is joined into the plasmid; the gene is cut out of human DNA; bacteria take up the plasmid.
Give two advantages of human insulin made by bacteria over insulin from the pancreases of cattle and pigs.
A bacterium divides every 30 minutes. Starting from one, how many bacteria could there be after 6 hours?
Explain why a patient treated by gene therapy for sickle-cell disease could still pass the sickle-cell allele to his or her children.
Explain how Bt maize can reduce the use of insecticide, and give one way this benefit could be lost over time.
"Every potato farmer in Rwanda should grow GM late-blight-resistant potatoes now." Evaluate this statement, giving at least one argument on each side and a conclusion.

Show answersHide answers

(a) Changing the DNA of an organism, usually by inserting a gene from another organism. (b) An organism whose DNA has been changed by genetic engineering.
(a) A restriction enzyme. (b) DNA ligase.
The gene is cut out of human DNA; a plasmid is cut open; the insulin gene is joined into the plasmid; bacteria take up the plasmid; bacteria multiply in a fermenter; insulin is purified.
Any two: it is identical to human insulin, so fewer allergic reactions; large amounts can be made quickly; the supply does not depend on slaughtered animals; it can be made very pure.
$\frac{6 \times 60}{30} = 12$ divisions, so $2^{12} = 4096$ bacteria.
Gene therapy changes somatic (body) cells such as bone-marrow cells, not the gametes, so the faulty allele is still in the cells that make sperm or eggs.
The maize makes its own Bt protein, which kills the caterpillars that feed on it, so the farmer does not need to spray as much. The caterpillars could evolve resistance if Bt maize is grown everywhere without other controls.
For: more reliable yields and fewer fungicide sprays. Against: the potatoes are not yet released (RAB, 2026) and must first pass regulation; seed cost, buyer acceptance, loss of diversity and possible resistance in the pathogen. A good conclusion: they could help once approved, if grown with good practice alongside other varieties, but "every farmer, now" ignores the approval process and the risks of growing only one variety.

Key points

Genetic engineering: cut a gene out with a restriction enzyme, join it into a vector (plasmid) with DNA ligase, and put it into a host cell.
Bacteria with the human insulin gene make human insulin in fermenters.
Gene therapy adds a working gene to a patient's somatic cells; it is not inherited.
GM crops can resist pests and disease or add nutrients; each must be weighed for benefits and risks and approved by regulators. In Rwanda, GM late-blight-resistant potatoes are in field trials (RAB, 2026).

1A human hormone made by bacteria

2How bacteria are made to produce human insulin

3Gene therapy

4Genetically modified crops

5In Rwanda

6Benefits and drawbacks of GMOs