Biotechnology and genetic engineering
Why bacteria are useful, and how genes are transferred between species.
Review these first
Learning objectives
What you need to be able to do
Teacher-mapped phrasing — check against the official Cambridge syllabus for exact wording.
- 21.1.1Describe the use of microorganisms in biotechnology, including anaerobic respiration in yeast.
- 21.1.2Outline genetic modification and discuss its advantages and disadvantages.Supplement
6 minute read
Biotechnology and genetic engineering
Why bacteria are so useful
Bacteria are ideal for industrial biotechnology because they reproduce very rapidly, have simple growth requirements, contain plasmids that make gene transfer straightforward, and there are fewer ethical concerns than with animals.
Familiar biotechnology
- Bread and beer rely on anaerobic respiration in yeast: glucose → ethanol + carbon dioxide. The CO₂ makes dough rise; the ethanol is the alcohol in beer.
- Yoghurt is made by bacteria fermenting lactose to lactic acid.
- Enzymes in washing powders — proteases digest protein stains, lipases digest fat stains, working at lower temperatures and saving energy.
Genetic modification
Genetic modification means changing an organism's genetic material by removing, adding or changing genes. The standard example is producing human insulin in bacteria, and the sequence is worth knowing:
- The human insulin gene is cut out of human DNA using restriction enzymes, leaving sticky ends.
- A bacterial plasmid is cut open with the same restriction enzyme, so the sticky ends match.
- The gene is inserted into the plasmid and joined using ligase.
- The plasmid is put back into a bacterium.
- The bacterium reproduces rapidly, and the whole population makes human insulin, which is extracted and purified.
Weighing it up
Advantages — insulin identical to human insulin, produced in large quantities cheaply and free from animal disease; crops modified for pest resistance or better nutrition, such as vitamin-A-enriched rice. Disadvantages — concerns about modified genes spreading to wild species, unknown long-term effects, the cost of seed for small farmers, and ethical objections to altering organisms.
Think of it like this
Restriction enzymes cut DNA the way scissors cut a jigsaw edge — because the same scissors cut both the gene and the plasmid, the two edges are complementary and slot together only the right way round.
Worked examples
Method, step by step
Describe how bacteria can be genetically modified to produce human insulin.
- 1The human insulin gene is cut out of human DNA using a restriction enzyme, producing sticky ends.
- 2A plasmid is removed from a bacterium and cut open with the same restriction enzyme, giving complementary sticky ends.
- 3The insulin gene is inserted into the plasmid and sealed in place using ligase.
- 4The recombinant plasmid is returned to a bacterium, which is then grown in a fermenter.
- 5The rapidly reproducing bacteria all express the gene, and the insulin is extracted and purified.
The insulin gene is cut from human DNA with a restriction enzyme, inserted into a plasmid cut with the same enzyme and joined with ligase, then the plasmid is put back into bacteria which are cultured to produce insulin in bulk.
Common misconceptions
- Thinking the same enzyme does the cutting and joining. **Restriction enzymes** cut; **ligase** joins.
- Believing GM insulin is "artificial" and different from human insulin. It is produced from the human gene, so the protein is identical — an advantage over the pig insulin used historically.
- Forgetting that both the human DNA and the plasmid must be cut with the *same* restriction enzyme, which is what makes the sticky ends complementary.
In the exam
- Name the two enzymes explicitly. "Restriction enzyme cuts, ligase joins" is worth easy marks and is frequently confused.
- For evaluation questions, give a genuine point on each side and then a conclusion. A list of advantages alone will not access the top marks.