(c) Genetic modification (genetic engineering)
- Syllabus
- 2024
- Topic
- —
- Level
- —
Learning objectives
5.12Restriction enzymes and DNA ligaseUnderstand how restriction enzymes are used to cut DNA at specific sites and ligase enzymes are used to join pieces of DNA together.5.13Genetic engineering vectorsUnderstand how plasmids and viruses can act as vectors, which take up pieces of DNA, and then insert this recombinant DNA into other cells.5.14Human insulin productionUnderstand how large amounts of human insulin can be manufactured from genetically modified bacteria that are grown in a fermenter.5.15GM plants in food productionUnderstand how genetically modified plants can be used to improve food production.5.16Transgenic organismsUnderstand that the term transgenic means the transfer of genetic material from one species to a different species.
Cut and join DNA with two enzyme tools
Genetic engineering uses restriction enzymes as sequence-specific DNA cutters and DNA ligase as the enzyme that joins DNA fragments.
| Enzyme | Action | Use in recombinant DNA |
|---|---|---|
| restriction enzyme | recognises a specific base sequence and cuts the DNA backbone at that site | cuts out the desired gene and opens vector DNA such as a plasmid |
| same restriction enzyme on donor and vector | produces matching ends on both DNA pieces | complementary ends can align by base pairing |
| DNA ligase | seals the sugar-phosphate backbones of adjacent DNA pieces | permanently joins the desired gene into the vector, forming recombinant DNA |
Cut donor DNA and vector with the same restriction enzyme, allow matching ends to pair, then use ligase to seal the join. Enzyme names must match their actions.
Restriction enzymes cut; ligase joins. Ligase does not remove the gene, and a restriction enzyme does not by itself insert or seal it into another DNA molecule.
Deliver recombinant DNA with plasmid or viral vectors
A vector carries recombinant DNA into a recipient cell; plasmids and modified viruses can both perform this delivery role.
| Vector | How recombinant DNA is carried and delivered |
|---|---|
| plasmid | a small circular DNA molecule is cut, joined to the desired gene and taken up by a recipient cell such as a bacterium |
| virus | viral genetic material is modified to include the desired DNA; infection delivers that DNA into a host cell |
| after delivery | cells containing the recombinant DNA can express the inserted gene if the required control sequences and cellular machinery are available |
Recombinant DNA contains DNA joined from different sources. The vector is the carrier; the inserted DNA is the genetic cargo; the recipient is the cell that takes it up.
A plasmid and a virus are not enzymes. Restriction enzyme and ligase construct recombinant DNA; the vector transports that DNA into another cell.
Manufacture human insulin with GM bacteria
Large amounts of human insulin can be made by inserting the human insulin gene into bacterial plasmids, growing the modified bacteria and recovering their protein product.
| Stage | Process |
|---|---|
| 1 obtain the gene | isolate or prepare DNA carrying the human insulin coding sequence |
| 2 construct vector | cut the insulin DNA and a bacterial plasmid with a restriction enzyme, then join them with ligase |
| 3 modify bacteria | introduce recombinant plasmids into bacterial cells and select cells that contain them |
| 4 scale growth | culture the selected GM bacteria in a fermenter with sterile nutrients, suitable temperature and pH, mixing and oxygen when required |
| 5 recover product | bacteria express the human gene; insulin is harvested and purified for medical use |
Bacteria reproduce rapidly and plasmids are copied as cells divide, so a controlled fermenter produces a large population expressing the same inserted gene.
The insulin gene is human, but the production cells are bacteria. The process requires both genetic modification and controlled culture; inserting a gene alone does not purify a usable medicine.
Improve food production with GM plants
A GM plant carries deliberately altered DNA so it expresses a characteristic that can increase usable yield, reduce losses or improve the food produced.
| Engineered characteristic | Food-production benefit | Important limit or risk |
|---|---|---|
| insect resistance | less crop eaten and potentially less insecticide needed | resistant pest populations may evolve; non-target effects must be assessed |
| herbicide resistance | weeds can be killed while the crop survives, reducing competition | herbicide use may affect other plants and gene flow to wild relatives is possible |
| resistance to viral disease | fewer plants become diseased, stabilising yield | effectiveness depends on the disease and trait |
| improved nutritional content | food can provide more of a needed nutrient, such as vitamin-A precursor in golden rice | access, diet, safety and acceptance still matter |
| stress tolerance or delayed spoilage | more crop survives difficult conditions or reaches consumers | ecological and food-safety evidence must be evaluated case by case |
Benefits are trait-specific, not properties of every GM crop. Compare yield, pesticide use, non-target organisms, gene flow, health evidence and farmer access for the actual plant and inserted gene.
GM changes DNA directly; selective breeding chooses parents and recombines existing alleles over generations. Neither method guarantees a higher yield in every environment.
Use the term transgenic precisely
A transgenic organism contains genetic material transferred from a different species.
| Description | Transgenic? |
|---|---|
| a bacterial cell receives a human insulin gene | yes: DNA crossed a species boundary |
| a crop receives a bacterial gene for an insect-resistant protein | yes: the donor and recipient are different species |
| DNA is altered without adding genetic material from another species | genetically modified, but not necessarily transgenic |
| two varieties of the same plant are selectively crossed | no: this is selective breeding, not direct interspecies gene transfer |
All transgenic organisms are genetically modified, but not every genetic modification is transgenic. The defining condition is transfer of genetic material between different species, not simply a changed phenotype.