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8.2.9Topic 8 · Grey Matter

Producing Drugs Using GMOs — Edexcel A Level Biology A (SNAB) 9BI0 Revision Notes & Topical Questions

5 min read 9 parts Lesson 20 of 22 1 quiz

📚 Edexcel A Level Biology A (SNAB) 9BI0 Hub / Topical Revision
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8.2.9 Producing Drugs Using GMOs — Edexcel A Level Biology A (SNAB) 9BI0 notes: Describe how genetically modified organisms are used to make drugs such as insulin, and evaluate the advantages and concerns.A genetically modified organism (GMO) has had its DNA altered, often by add…

  • Exam-style question 1
  • Exam-style question 2
  • Exam-style question 3
  • Recombinant plasmid
  • Restriction enzyme
  • DNA ligase

Section 1 of 9Why use GMOs for drugs?

A genetically modified organism (GMO) has had its DNA altered, often by adding a gene from another species.

Why use GMOs for drugs?
Such organisms can be used as living factories to make human proteins in large quantity.
This is useful for drugs that are proteins,
  • such as insulin for diabetes, human growth hormone and clotting factor VIII for haemophilia,
  • and many antibodies.
The first genetically engineered drug was human insulin, which replaced insulin taken from pigs and cattle.

Section 2 of 9Making human insulin in bacteria

1
The human insulin gene is obtained: either cut from human DNA with restriction enzymes,
  • or made from mRNA using reverse transcriptase to form cDNA (which lacks introns,
  • so bacteria can express it) or synthesised artificially.
2
A plasmid vector is cut with the same restriction enzyme, leaving complementary sticky ends.
3
The gene and plasmid are joined by DNA ligase to make recombinant plasmid.
4
The plasmid is inserted into bacteria, for example by heat shock in the presence of calcium ions.
5
Cells that have taken up the plasmid are identified, using a marker gene such as antibiotic resistance, and grown in a fermenter.
6
The insulin is harvested and purified.

A promoter sequence must be present so that the gene is transcribed in the host. Yeast and other eukaryotic cells are also used when the protein needs processing after translation.

Section 3 of 9Other organisms

Some drugs are made in genetically modified animals or plants, so-called "pharming". For example, a human protein can be produced in the milk of transgenic goats, from which it is purified. Plants and cultured mammalian cells are used to make complex proteins that need correct folding or modification.

Section 4 of 9Advantages and concerns

AdvantagesConcerns
Human protein, so less risk of immune rejection or allergy than animal insulinCost of equipment and regulation
Large, reliable supply, not dependent on animal slaughterEthical concerns about altering organisms, especially animals
Reduced risk of infection from animal tissuePossible escape of GMOs or spread of resistance genes
Can be produced to high purity at relatively low costPatents may make drugs expensive for some countries

Section 5 of 9Links

This topic uses ideas from DNA technology, enzymes, protein synthesis and the nature of the genetic code (the same code is used in all organisms, so human genes work in bacteria). It also links to personalised medicine and drug treatments for brain disease.

Section 6 of 9Growing the cells and checking the product

After the recombinant bacteria are obtained, they are grown on a large scale in a fermenter, a sterile steel vessel in which the conditions are controlled to give the highest yield.

Growing the cells and checking the product
Oxygen is supplied by sparging, the culture is stirred to keep nutrients and cells evenly mixed, the temperature and pH are monitored and kept at the optimum,
  • and a cooling jacket removes the heat released by metabolism.
Aseptic technique prevents contamination by other microorganisms that would compete for nutrients and reduce yield.
In batch culture the whole culture is harvested at the end, whereas in continuous culture nutrients are added and product is removed constantly.

The insulin is then separated from the cells and purified, usually by filtration and chromatography, since a drug must be free from bacterial proteins and toxins that could cause a reaction. The final product is tested for purity and activity before it is released for use.

Identifying which cells have taken up the plasmid is a frequent exam question.

1
Plasmids used as vectors usually carry marker genes, such as antibiotic resistance genes.
2
After transformation, bacteria are spread on agar containing the antibiotic and only transformed cells survive.
3
In a more refined approach, the gene is inserted into the middle of a second marker gene so that successful insertion inactivates it.
4
Cells with the recombinant plasmid then grow on one antibiotic but not on another, and can be identified by replica plating.
5
Fluorescent markers such as GFP can also be used, since glowing colonies are easy to select.

Regulation requires that each batch is tested and that facilities follow good manufacturing practice. Contained use of GM bacteria in closed fermenters limits the risk of release, and the organisms are often engineered to be unable to survive outside the laboratory.

Section 7 of 9Exam-style questions

  1. Describe how a human gene is inserted into a bacterial plasmid. [4]4 marks

  2. Explain why the gene used in bacteria is often made from mRNA rather than cut from human DNA. [2]2 marks

  3. State two advantages of insulin made by GM bacteria compared with pig insulin. [2]2 marks

Section 8 of 9Key terms

TermMeaning
GMOOrganism with genetic material altered by technology
Recombinant plasmidPlasmid containing DNA from another source
Restriction enzymeEnzyme cutting DNA at specific base sequences
DNA ligaseEnzyme joining DNA fragments
cDNADNA copied from mRNA using reverse transcriptase
VectorCarrier, such as a plasmid, used to transfer a gene
TransgenicContaining a gene from another species

Section 9 of 9Exam technique

1
Saying that bacteria "make" the gene; they express it by transcription and translation.
2
Forgetting DNA ligase when describing joining.
3
Using the same restriction enzyme for the gene and plasmid is essential for complementary sticky ends.
4
Describing the genetic code as different in bacteria; it is universal.

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