Genetic Modification (Genetic Engineering)Edexcel IGCSE Biology: Revision notes
Section 1
What tools are used to cut and join DNA?
Genetic engineering relies on two key enzymes:
- Restriction enzymes — cut DNA at specific base sequences, allowing a desired gene to be removed from one organism's DNA (and cutting open a vector's DNA to receive it)
- Ligase enzymes — join pieces of DNA together, sealing the desired gene into a vector
Restriction enzymes often leave 'sticky ends' — short, single-stranded overhangs that allow complementary DNA fragments to join together more easily.
Always name both enzymes and their specific roles — 'restriction enzyme cuts, ligase joins' — as separate marking points.
Section 2
What are vectors, and how is recombinant DNA made?
A vector is used to carry a piece of DNA into another cell. Common vectors include:
- Plasmids — small circular pieces of DNA found in bacteria, which can take up and carry a new gene
- Viruses — can be used to insert genetic material into a host cell
The process: a gene is cut from an organism's DNA using a restriction enzyme; a plasmid is cut open using the same restriction enzyme; the gene is inserted into the plasmid and sealed using ligase, forming recombinant DNA; the plasmid (vector) is then taken up by a host cell (e.g. a bacterium), inserting the recombinant DNA.
Section 3
How is human insulin manufactured using genetic engineering?
The human insulin gene is inserted into bacterial plasmids using restriction and ligase enzymes. The modified (genetically engineered) bacteria are grown in large numbers in an industrial fermenter under controlled conditions (aseptic, nutrients, optimum temperature/pH, oxygenation, agitation). As the bacteria multiply and express the inserted gene, they produce large quantities of human insulin, which is then extracted and purified for use by people with diabetes.
Before genetic engineering, insulin for diabetics had to be extracted from animal pancreases; genetically modified bacteria now allow large-scale, human-identical insulin production.
Section 4
How can genetically modified plants improve food production?
Genes can be inserted into crop plants to give them useful new characteristics, improving food production, for example:
- Resistance to herbicides (allowing weed control without harming the crop)
- Resistance to pests or disease (reducing crop losses, less need for pesticides)
- Improved nutrient content (e.g. added vitamins)
- Increased yield or tolerance to environmental stress (e.g. drought)
These genetically modified crops can increase the amount and reliability of food produced from a given area of land.
Section 5
What does transgenic mean?
Transgenic describes the transfer of genetic material from one species into a different species. An organism that has received a gene from another species (e.g. a crop plant with a bacterial gene, or a bacterium with a human gene) is described as transgenic.
A transgenic organism is not the same as a hybrid from selective breeding — transgenic specifically means DNA has been moved between different species using genetic engineering.
Must Know
- Restriction enzymes cut DNA at specific sites; ligase enzymes join pieces of DNA together
- Plasmids and viruses act as vectors, carrying recombinant DNA into other cells
- Genetically modified bacteria, grown in a fermenter, can mass-produce human insulin
- Genetically modified plants can improve food production (e.g. pest/herbicide resistance, better nutrition, higher yield)
- Transgenic means genetic material has been transferred from one species to a different species
That's the notes covered.
Carry on to the next subtopic.