To make 'artificial' human insulin, it is necessary to find the genetic code for the insulin polypeptide on the human chromosomes. This gene is 'cut out' of the chromosome using a bacterial restriction enzyme, and the insulin gene is then spliced into a loop of bacterial DNA using a ligase enzyme. The DNA loop is then inserted back into a bacterium, which divides rapidly producing millions of identical bacteria all possessing the insulin gene and manufacturing the 'artificial' hormone.
