Genetic engineering of bacteria

• Restriction enzymes make staggered cuts in DNA molecules, producing sections with a few unpaired bases at each end -'sticky ends'. A section of DNA containing the gene for making insulin is cut from a human chromosome in this way.

• Restriction enzymes are also used to cut plasmids open. By using the same restriction enzyme as was used on the human chromosome DNA, the cut plasmids have the same sticky ends.

• Sections of DNA containing the insulin gene are mixed with the cut plasmids. The complemenatry bases on the sticky ends pair up. An enzyme called ligase is used to join the ends together.

• The plasmids are then inserted back into bacteria, which are then grown in huge tanks. The insulin they now make can be easily extracted.

Any DNA molecule which is used to carry new DNA into another cell is called a vector.