Free Genetic Modification OCR A Level Biology revision notes – covering specification points 6.1.3(fi) and 6.1.3(fii).
Genetic modification is the intentional modification of an organism’s genome using genetic engineering.
Genetic Engineering
Genetic engineering refers to the techniques and tools used to change an organism’s DNA.
Traditional approaches to genetic engineering involve the isolation of a desired gene and its incorporation into a vector (e.g. a plasmid) using restriction enzymes.
The process of forming a recombinant DNA plasmid can be simplified into the following stages:
- The desired gene and the plasmid are cut with the same restriction enzyme, producing complementary sticky ends.
- The cut gene and opened plasmid are mixed, and their sticky ends pair up, held together by hydrogen bonds.
- DNA ligase joins the gene with the plasmid by forming phosphodiester bonds, producing a recombinant plasmid.
Transformation of the host cell involves getting the desired gene into the target cell.
The table below outlines some of the techniques used to introduce the recombinant DNA or its vector into the target cell:
| Technique | Description |
|---|---|
| Agrobacterium tumefaciens | This bacterium naturally transfers part of its plasmid into plant cells and is used as a vector to introduce genes into plant cells. |
| Electroporation | A high-voltage pulse is applied to the target cells to create temporary pores in the cell surface membrane through which DNA can enter. |
| Transduction* | A bacteriophage** is used to deliver the DNA into the host cell. |
*The official OCR A Level Biology textbook refers to the use of bacteriophages as an example of ‘transfection’. Historically, ‘transfection’ was used to describe using bacteriophages to deliver recombinant DNA into bacteria. However, contemporarily this is known as ‘transduction’, whilst ‘transfection’ refers to the use of chemical or physical methods (e.g. electroporation) to introduce non-viral DNA or RNA into eukaryotic cells.
**A virus that infects bacteria.