Recombinant DNA and Biotechnology
Biotechnology is an industrial process that uses the scientific research on DNA for practical benefits. Biotechnology is synonymous with genetic engineering because the genes of an organism are changed during the process and the DNA of the organism is recombined. Recombinant DNA and biotechnology can be used to form proteins not normally produced in a cell. In addition, bacteria that carry recombinant DNA can be released into the environment to increase the fertility of the soil, serve as an insecticide, or relieve pollution.
Tools of biotechnology. The basic process of recombinant DNA technology revolves around the activity of DNA in the synthesis of protein. By intervening in this process, scientists can change the nature of the DNA and of the gene make-up of an organism. By inserting genes into the genome of an organism, the scientist can induce the organism to produce a protein it does not normally produce.
The technology of recombinant DNA has been made possible in part by extensive research on microorganisms during the last century. One important microorganism in recombinant DNA research isEscherichia coli (E. coli). The biochemistry and genetics ofE. coli are well known, and its DNA has been isolated and made to accept new genes. The DNA can then be forced into fresh cells of E. coli, and the bacteria will begin to produce the proteins specified by the foreign genes. Such altered bacteria are said to have been transformed.
Interest in recombinant DNA and biotechnology heightened considerably in the 1960s and 1970s with the discovery of restriction enzymes. These enzymes catalyze the opening of a DNA molecule at a “restricted” point, regardless of the DNA's source. Moreover, certain restriction enzymes leave dangling ends of DNA molecules at the point where the DNA is open. (The most commonly used restriction enzyme is namedEcoRl.) Foreign DNA can then be combined with the carrier DNA at this point. An enzyme called DNA ligase is used to form a permanent link between the dangling ends of the DNA molecules at the point of union (Figure 1 ).
Figure 1
The production of a a recombined bacterium using a gene from a foreign donor and the synthesis of protein encoded by the recombinant DNA molecule.
The genes used in DNA technology are commonly obtained from host cells or organisms called gene libraries. A gene library is a collection of cells identified as harboring a specific gene. For example, E. coli cells can be stored with the genes for human insulin in their chromosomes.
Pharmaceutical products. Gene defects in humans can lead to deficiencies in proteins such as insulin, human growth hormone, and Factor VIII. These protein deficiencies may lead to problems such as diabetes, dwarfism, and impaired blood clotting, respectively. Missing proteins can now be replaced by proteins manufactured through biotechnology. For insulin production, two protein chains are encoded by separate genes in plasmids inserted into bacteria. The protein chains are then chemically joined to form the final insulin product. Human growth hormone is also produced within bacteria, but special techniques are used because the bacteria do not usually produce human proteins. Therapeutic proteins produced by biotechnology include a clot-dissolving protein calledtissue plasminogen activator (TPA) and interferon. This antiviral protein is produced withinE. coli cells. Interferon is currently used against certain types of cancers and for certain skin conditions.
Vaccines represent another application of recombinant DNA technology. For instance, the hepatitis B vaccine now in use is composed of viral protein manufactured by yeast cells, which have been recombined with viral genes. The vaccine is safe because it contains no viral particles. Experimental vaccines against AIDS are being produced in the same way.
Diagnostic testing. Recombinant DNA and biotechnology have opened a new era of diagnostic testing and have made detecting many genetic diseases possible. The basic tool of DNA analyses is a fragment of DNA called the DNA probe. A DNA probe is a relatively small, single-stranded fragment of DNA that recognizes and binds to a complementary section of DNA in a complex mixture of DNA molecules. The probe mingles with the mixture of DNA and unites with the target DNA much like a left hand unites with the right. Once the probe unites with its target, it emits a signal such as radioactivity to indicate that a reaction has occurred.
