Genetic Engineering
Use of Biological Resources · 6 question types
What Genetic Engineering Is
Genetic engineering (also called genetic modification, GM) is the process of deliberately changing an organism's DNA by inserting a gene from a different organism, usually to give it a useful new characteristic
In selective breeding (topic 17), the alleles being shuffled around already exist within the species. Genetic engineering goes much further: it lets scientists take a gene from any species and insert it into the DNA of any other species. This is possible because the genetic code is universal: every living thing uses the same four DNA bases (A, T, G, C) and the same code (three-base codons) to specify amino acids. A human gene placed inside a bacterium still codes for the same human protein.
Some terminology
| Term | Meaning |
|---|---|
| Genetically modified organism (GMO) | Any organism whose DNA has been deliberately altered |
| Transgenic organism | A GMO that contains DNA from a different species (a subset of GMOs) |
| Recombinant DNA | DNA that has been built from pieces of more than one source organism |
| Vector | A "carrier" molecule used to insert the new gene into the host cell. Usually a bacterial plasmid or a virus |
| Restriction enzyme | A bacterial enzyme used to cut DNA at specific base sequences |
| DNA ligase | An enzyme used to join two pieces of DNA together |
A useful memory aid: picture restriction enzymes as the scissors that cut DNA, and ligase as the glue that joins it back together.
Naming the two enzymes and their roles
What comes up: a 2-mark question asking you to give the roles of two named enzymes used to produce a recombinant plasmid.
Write (two marks): (1) A restriction enzyme cuts the DNA/gene out (and cuts open the plasmid), leaving sticky ends. (2) DNA ligase joins the gene into the plasmid (seals the sticky ends together).
Watch out: writing "lipase" instead of "ligase" scores zero — the mark scheme explicitly rejects "lipase". Also make sure you name both enzymes; "an enzyme cuts and another joins" without the names earns nothing.