Recombinant DNA technology has extensive applications in developing pharmaceuticals. The first drug created using recombinant DNA was human insulin. To make the recombinant DNA, the insulin gene is cut from human DNA with restriction enzymes. The DNA is then placed in a vector, such as a plasmid, and another enzyme, DNA ligase, seals the plasmid containing the insulin gene. The plasmid is placed into another bacterial cell and this new cell produces multiple copies of the gene, called clones, when it divides. The host bacterial cell also expresses the gene product, in this case insulin. This technology is possible because the genetic code is universal. DNA functions in the same way, whether in a human cell or a bacterial cell.

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