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Cloning

Author(s): Joseph G. Marx, PhD

Recombinant DNA Technology

To clone DNA, scientists use restriction enzymes to cut out the specific DNA segment to be replicated (copied). The segment then is inserted into a bacterial plasmid for replication. Bacterial plasmids are circular DNA molecules distinct from the normal bacterial genome and are capable of replicating separately. Once inserted, the recombinant DNA is replicated, along with the host cell's DNA. Plasmids can carry up to 20,000 base pairs of foreign DNA.

Human insulin often is produced by recombinant DNA technology. The human insulin gene is inserted into a bacterial plasmid and can be induced to produce vast quantities of insulin for the treatment of diabetes. Other specific applications of recombinant DNA technology include the production of human growth hormone, erythropoietin for kidney dialysis patients, clotting factor for hemophiliacs, and hepatitis B vaccine. Although viruses, bacterial artificial chromosomes (BACs), and yeast artificial chromosomes (YACs) also may be used for replicating DNA, bacterial plasmids are most commonly used in this technology.