The process of genetic engineering – Higher
The main steps of genetic engineering:
- restriction endonuclease enzymeAn enzyme that can cut DNA in specific places in the DNA molecule. are used to isolate the required geneThe basic unit of genetic material inherited from our parents. A gene is a section of DNA which controls part of a cell's chemistry - particularly protein production. from the chromosomeThe structure made of DNA that codes for all the characteristics of an organism.. They cut the DNA at a specific sequence. Restriction enzymes leave sticky endsOverhangs of single stranded DNA made by restriction enzymes. that are overhangs of DNA.
- A vectorThe way in which genetic material is transferred from a donor to a recipient e.g. plasmids and artificial chromosomes. is needed to get the gene into the host cell. This is usually a plasmidThe small circular genetic material present in bacterial cells and used in DNA recombinant technology. that is taken from a bacterial cell. The plasmid is cut with the same restriction enzymes so it gets the same sticky ends.
- The sticky ends on the plasmid stick with the ones on the gene.
- The gene and the plasmid are joined together using an enzyme called DNA ligaseAn enzyme that can join pieces of DNA together..
- The vector is transferred back into the bacteria host cells.
- The host cells now have a gene from another organism and so are said to be transgenicDescribes an organism that has undergone genetic modification and has had genes transferred from another unrelated organism..
This diagram shows how the genetic engineering of insulin works. Insulin can be produced by bacteria and then purified and used to regulate type 1 diabetes.
Selection of transgenic bacteria
Not all of the host cell bacteria will take up the plasmid again once it has had the desired gene added to it. It is important that scientists can select the transgenic bacteria.
The plasmids often have antibioticSubstance that controls the spread of bacteria in the body by killing them or stopping them reproducing. resistance genes in them, if a bacterial cell does take up the plasmid again, then antibiotics cannot kill it. If a bacterial cell does not take up the plasmid then it does not have the antibiotic resistance genes and it will die.
Scientists can treat the bacterial population with an antibiotic. They know that the ones that survive are the transgenic ones. This is called selection, as you are selecting for the bacteria that have the plasmid with the desired gene in it.
Restriction enzymes
Restriction enzymes do not cut directly across the double strand of DNA because this would involve cutting any section of DNA into many different pieces and it would not be easy to remove an entire gene.
Instead, restriction enzymes cut across the double strands at two different places. The place where they cut across the DNA is called a sticky end. Restriction enzymes can be used to cut out specific genes, and also cut open places in the plasmid DNA where the genes will fit exactly.
More guides on this topic
- Field investigations - OCR Gateway
- Monitoring and maintaining the environment - OCR Gateway
- Monitoring & maintaining health - communicable diseases - OCR Gateway
- Treating, curing and preventing disease - OCR Gateway
- Cancer and cardiovascular disease - non-communicable - OCR Gateway
- Monitoring and maintaining health - non-communicable - OCR Gateway