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Recombinant DNA

Deoxyribonucleic acid (DNA) is the information blueprint that exists in most living organisms. Some viruses instead contain ribonucleic acid (RNA). Even these viruses require the production of DNA at some stage of their replication.

DNA from different organisms of the same species combines together naturally to yield an organism that has traits from both parent organisms. There is also evidence accumulating that DNA transfer between different species may be a natural process. However, much interspecies mixing of DNA is the result of deliberate experimental manipulations.

A crucial process of these manipulations is the preparation of recombinant DNA. Recombinant DNA is DNA from different organisms that have been chemically bonded together to form a single DNA. The recombinant DNA can be interpreted by the various enzymes of prokaryotic or eukaryotic cells, so that the genes contained in the recombinant DNA can be expressed and the protein products produced.

The recombination can involve the DNA from two eukaryotic organisms, two prokaryotic organisms, or between an eukaryote and a prokaryote. An example of the latter is the production of human insulin by the bacterium Escherichia coli, which has been achieved by splicing the gene for insulin into the E. coli genome such that the insulin gene is expressed and the protein product formed.

The splicing of DNA from one genome to another is done using two classes of enzymes. Isolation of the target DNA sequence is done using restriction enzymes. There are well over a hundred restriction enzymes, each cutting in a very precise way a specific base of the DNA molecule. Used singly or in combination, the enzymes allow target segments of DNA to be isolated. Insertion of the isolated DNA into the recipient genome is done using an enzyme called DNA ligase.

Typically, the recombinant DNA forms part of the DNA making up a plasmid. A plasmid is a circular piece of DNA that exists outside of the main body of genetic material. The mobility of the plasmid facilitates the easy transfer of the recombinant DNA from the host organism to the recipient organism.

Molecular biologist Paul Berg of Stanford University first achieved the manufacture of recombinant DNA in 1972. Berg isolated a gene from a human cancer-causing monkey virus, and then joined the oncogene into the genome of the bacterial virus lambda. For this and subsequent recombinant DNA studies (which followed a voluntary one-year moratorium from his research while safety issues were addressed) he was awarded the 1980 Nobel Prize in chemistry.

In 1973, Stanley Cohen and Herbert Boyer created the first recombinant DNA organism, by adding recombinant plasmids to E. coli. Since that time, advances in molecular biology techniques, in particular the development of the polymerase chain reaction, have made the construction of recombinant DNA swifter and easier. Cohen and Boyer's accomplishment was the birth of modern biotechnology, and spawned the resulting biotechnology industry.

Recombinant DNA has been of fundamental importance in furthering the understanding of genetic regulatory processes and shows great potential in the genetic design of therapeutic strategies.

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