• In genetic engineering genes are taken from one organism and inserted into another. Genes that code for useful substances, such as hormones, enzymes and antibiotics, are often transferred into micro-organisms, which then produce large quantities of these substances.
  • The gene is cut out from the DNA of the donor organism using a restriction endonuclease enzyme. This cuts out the relevant section of the organism's DNA, leaving sticky ends - which consist of a single strand with a few base pairs - that will enable the gene to be inserted into a small circular piece of bacterial DNA called a plasmid.
  • Plasmids are often used as vectors to take the selected gene into bacterial cells. Plasmids occur naturally in cells and replicate independently of the main bacterial DNA.
  • The same restriction endonuclease is used to cut the plasmid. This leaves complementary sticky ends to which the selected gene can be attached
  • The sticky ends of the gene and the open plasmid are joined together by ligase which is another enzyme.
  • The plasmids are then introduced into the target organism, and transformed cells are selected and cloned.
  • Genetic markers in the plasmids, such as genes that confer antibiotic resistance, enable genetic engineers to identify bacteria that have successfully taken up the selected gene.
  • Transformed bacteria are cultured on a large scale in industrial fermenters and the useful product is then extracted.