Recombinant Dna Technology and Genetic Engineering
Recombinant deoxyribonucleic acid (DNA) is DNA that has been created artificially. DNA from two or more sources is incorporated into a single recombinant molecule. The technologies used to accomplish this are collectively referred to as recombinant DNA technology.
Recombinant DNA technology relies upon restriction endonucleases—enzymes that recognize certain sequences within the DNA, and cut the DNA at the particular site. Many restriction endonucleases exist that recognize many sequences of DNA bases. Some of the enzymes create a staggered cut, where one strand of DNA is longer than the complimentary strand. Because of the staggered cuts, treatment of different DNA with the restriction enzymes will generate regions, which compliment one another. These regions will anneal together. These behaviors allow foreign DNA to be inserted into target DNA. This is the basis of recombinant DNA technology.
To be useful, the recombinant molecule must be replicated many times to provide material for subsequent experimental manipulations. Producing many identical copies of the same recombinant molecule is called cloning. Cloning can be done in the laboratory, using the technique called the polymerase chain reaction.
Recombinant DNA technology also uses living organisms, such as bacteria, yeast and mammalian cells to achieve cloning. The DNA is taken up by the cell when incorporated in a vector. Viruses and plasmids typically are utilized as vectors. The bacterium Agrobacterium tumefaciens is a popular means of transforming plants. The DNA shuttled by the vector to the host typically contains a gene that encodes resistance to an antibiotic, or other feature, such as the ability to fluoresce when exposed to ultraviolet light. These act as indicators to permit a means of monitoring the success of DNA integration and protein expression. For example, exposure of the bacteria Escherichia coli to vectors containing the recombinant DNA will produce some cells that have successfully incorporated and expressed the DNA. If the recombinant indicator is an antibiotic resistance gene, then the successful cells can be detected when they form colonies on a growth substrate containing the antibiotic. Each colony represents a clone of transformed cells. Selecting recombinant plants can be done in a similar fashion, with the recombinant insert containing a herbicide-resistance gene and the growth medium containing the herbicide.
Recombinant DNA technology is used in human therapy. Many human genes have been cloned in E.coli or in yeast. This has made it possible to produce unlimited quantities of human protein in the laboratory. Cultured cells transformed with the human gene are being used to manufacture insulin for diabetes, factor VIII for males suffering from hemophilia A, factor IX for hemophilia B, human growth hormone, erythropoietin for the treatment of anemia, interferons, interleukins, factors for stimulating bone marrow after a bone marrow transplant, tissue plasminogen activator for dissolving blood clots, and adenosine deaminase for the treatment of some forms of severe combined immune deficiency.
Production of transgenic organisms has also created a great number of possibilities using plants. Transgenic plants have been obtained that express antibodies and recombinant pharmaceuticals. Molecular techniques combined with the traditional techniques of plant breeding are being utilized by the forestry industry to generate trees of commercial interest that are capable of faster and straighter growth. Transgenic crop plants, engineered to resist pests or targeted herbicides, have proved very popular. In 1999, the area planted to transgenic varieties was approximately half the U.S. soybean crop and about 25 per cent of the country's corn crop.
Future applications of recombinant DNA technology include food crops engineered to produce edible vaccines. This strategy would make vaccination more readily available to children worldwide. Because of their use across many cultures and their ability to adapt to tropical and subtropical environments, bananas have be the object of considerable research effort. Transgenic bananas containing inactivated viruses that cause cholera, hepatitis B and diarrhea has been produced and is undergoing evaluation.
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