4.4.8 Outline a basic technique used for gene transfer involving plasmids, a host cell (bacterium, yeast or other cell), restriction enzymes (endonucleases) and DNA ligase.

Gene transfer is when a gene from one organism is taken and placed in another organism.

Stage 1 is obtaining the gene for transfer. This is done by using restriction enzymes to cut out the useful gene that is to be transferred; this leaves sticky ends on each side of the gene.

Stage 2 is preparing a vector for the transferred gene. This is done by using plasmids which are small circular DNA molecules found in bacteria. These are cut with the same restriction enzyme and this leaves the same complementary 'sticky ends' in the plasmid like the ones on the gene.

Stage 3 is the when gene has to be copied and this is when the gene is combined with the DNA. The gene is glued into the plasmid using DNA ligase. This plasmid is called a recombinant DNA and it can be used as a vector.

Stage 4 is the isolation of the transformed cells. The vector is then put into the genome of a host cell (bacterium, yeast or other cell) as the bacteria gives the plasmid the ideal conditions to grow and this is done by putting it into a bioreactor. Many of the cells remain untransformed but some of the cells are transformed to contain the recombinant DNA and these transformed cells will be separated from untransformed. 

Stage 5 is obtaining the final product. This is done when the transformed cells are isolated and put into a fermenter the right to be cloned. The bacteria with the Recombinant DNA are then grown by asexual reproduction and the final step is to isolate and purify the product called downstream processing.