<P> The most common application of recombinant DNA is in basic research, in which the technology is important to most current work in the biological and biomedical sciences . Recombinant DNA is used to identify, map and sequence genes, and to determine their function . rDNA probes are employed in analyzing gene expression within individual cells, and throughout the tissues of whole organisms . Recombinant proteins are widely used as reagents in laboratory experiments and to generate antibody probes for examining protein synthesis within cells and organisms . </P> <P> Many additional practical applications of recombinant DNA are found in industry, food production, human and veterinary medicine, agriculture, and bioengineering . Some specific examples are identified below . </P> <Dl> <Dt> Recombinant chymosin </Dt> <Dd> Found in rennet, chymosin is an enzyme required to manufacture cheese . It was the first genetically engineered food additive used commercially . Traditionally, processors obtained chymosin from rennet, a preparation derived from the fourth stomach of milk - fed calves . Scientists engineered a non-pathogenic strain (K - 12) of E. coli bacteria for large - scale laboratory production of the enzyme . This microbiologically produced recombinant enzyme, identical structurally to the calf derived enzyme, costs less and is produced in abundant quantities . Today about 60% of U.S. hard cheese is made with genetically engineered chymosin . In 1990, FDA granted chymosin "generally recognized as safe" (GRAS) status based on data showing that the enzyme was safe . </Dd> <Dt> Recombinant human insulin </Dt> <Dd> Almost completely replaced insulin obtained from animal sources (e.g. pigs and cattle) for the treatment of insulin - dependent diabetes . A variety of different recombinant insulin preparations are in widespread use . Recombinant insulin is synthesized by inserting the human insulin gene into E. coli, or yeast (Saccharomyces cerevisiae) which then produces insulin for human use . </Dd> <Dt> Recombinant human growth hormone (HGH, somatotropin) </Dt> <Dd> Administered to patients whose pituitary glands generate insufficient quantities to support normal growth and development . Before recombinant HGH became available, HGH for therapeutic use was obtained from pituitary glands of cadavers . This unsafe practice led to some patients developing Creutzfeldt--Jakob disease . Recombinant HGH eliminated this problem, and is now used therapeutically . It has also been misused as a performance - enhancing drug by athletes and others . DrugBank entry </Dd> <Dt> Recombinant blood clotting factor VIII </Dt> <Dd> A blood - clotting protein that is administered to patients with forms of the bleeding disorder hemophilia, who are unable to produce factor VIII in quantities sufficient to support normal blood coagulation . Before the development of recombinant factor VIII, the protein was obtained by processing large quantities of human blood from multiple donors, which carried a very high risk of transmission of blood borne infectious diseases, for example HIV and hepatitis B. DrugBank entry </Dd> <Dt> Recombinant hepatitis B vaccine </Dt> <Dd> Hepatitis B infection is controlled through the use of a recombinant hepatitis B vaccine, which contains a form of the hepatitis B virus surface antigen that is produced in yeast cells . The development of the recombinant subunit vaccine was an important and necessary development because hepatitis B virus, unlike other common viruses such as polio virus, cannot be grown in vitro . Vaccine information from Hepatitis B Foundation </Dd> <Dt> Diagnosis of infection with HIV </Dt> <Dd> Each of the three widely used methods for diagnosing HIV infection has been developed using recombinant DNA . The antibody test (ELISA or western blot) uses a recombinant HIV protein to test for the presence of antibodies that the body has produced in response to an HIV infection . The DNA test looks for the presence of HIV genetic material using reverse transcription polymerase chain reaction (RT - PCR). Development of the RT - PCR test was made possible by the molecular cloning and sequence analysis of HIV genomes . HIV testing page from US Centers for Disease Control (CDC) </Dd> <Dt> Golden rice </Dt> <Dd> A recombinant variety of rice that has been engineered to express the enzymes responsible for β - carotene biosynthesis . This variety of rice holds substantial promise for reducing the incidence of vitamin A deficiency in the world's population . Golden rice is not currently in use, pending the resolution of regulatory and intellectual property issues . </Dd> <Dt> Herbicide - resistant crops </Dt> <Dd> Commercial varieties of important agricultural crops (including soy, maize / corn, sorghum, canola, alfalfa and cotton) have been developed that incorporate a recombinant gene that results in resistance to the herbicide glyphosate (trade name Roundup), and simplifies weed control by glyphosate application . These crops are in common commercial use in several countries . </Dd> <Dt> Insect - resistant crops </Dt> <Dd> Bacillus thuringeiensis is a bacterium that naturally produces a protein (Bt toxin) with insecticidal properties . The bacterium has been applied to crops as an insect - control strategy for many years, and this practice has been widely adopted in agriculture and gardening . Recently, plants have been developed that express a recombinant form of the bacterial protein, which may effectively control some insect predators . Environmental issues associated with the use of these transgenic crops have not been fully resolved . </Dd> </Dl> <Dd> Found in rennet, chymosin is an enzyme required to manufacture cheese . It was the first genetically engineered food additive used commercially . Traditionally, processors obtained chymosin from rennet, a preparation derived from the fourth stomach of milk - fed calves . Scientists engineered a non-pathogenic strain (K - 12) of E. coli bacteria for large - scale laboratory production of the enzyme . This microbiologically produced recombinant enzyme, identical structurally to the calf derived enzyme, costs less and is produced in abundant quantities . Today about 60% of U.S. hard cheese is made with genetically engineered chymosin . In 1990, FDA granted chymosin "generally recognized as safe" (GRAS) status based on data showing that the enzyme was safe . </Dd>

3 ways that recombinant dna has been used in modern medicine
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