Bacteria -research material II

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quantities of material with which to work. The process of engineering a DNA fragment into a vector is called "cloning," because multiple copies of an identical molecule are produced. Another way, recently discovered, of produsufficient cing many identical copies of a particular DNA fragment is polymerase chain reaction. This method is rapid and avoids the need for cloning DNA into a vector. Therapy. form of genetic engineering involves supplying a functional gene to cells lacking that function, with the aim of correcting a genetic disorder or acquired disease. Gene therapy can be broadly divided into two categories. The first is alteration of germ cells, that is, sperm or eggs, which results in a permanent genetic change for the whole organism and subsequent generations. This "germ line gene therapy" is not considered an option in humans for ethical reasons. The second type of gene therapy, somatic cell therapy, is analogous to an organ transplant. In this case, one or more specific tissues is targeted by direct treatment or by removal of the tissue, addition of the therapeutic gene or genes in the laboratory, and return of the treated cells to the patient. Several clinical trials of somatic cell gene therapy have started, mostly for the treatment of cancers and blood and liver and lung disorders. . process of genetic engineering has great potential. For example, the gene for insulin (q.v.) , naturally found only in the pancreas tissue of higher animals, can now be introduced into bacterial cells by way of a plasmid vector. The bacteria can then be grown in large quantities, giving an abundant source of so-called "recombinant" insulin at a relatively low cost. Production of recombinant insulin is also not dependent on the sometimes variable supply of pancreas tissue from abattoirs. Another important use of genetic engineering is in the manufacture of recombinant factor VIII, the blood clotting agent missing in patients with hemophilia A ( see Hemophilia A; ). Virtually all hemophiliacs who received factor VIII before the mid-1980s have contracted AIDS or hepatitis C ( see Hepatitis ) from viral contaminants in the blood used to make the product. Since that time, donor blood has been screened for the presence of HIV (Human Immunodeficiency Virus) and hepatitis C virus, and the manufacturing process includes steps to inactivate these viruses if they should be present. The possibility of viral contamination, however, is eliminated completely with the use of recombinant factor VIII. Other uses of genetic engineering include increasing the disease resistance of crops, producing pharmaceutical compounds in the milk of animals, generating vaccines, and altering livestock traits. . the potential benefits of genetic engineering are considerable, so may be the potential dangers. For example, the introduction of cancer-causing genes into a common infectious organism, such as the influenza virus, could be hazardous. Consequently, experiments with recombinant DNA are closely regulated and those involving infectious agents are permitted only under the strictest conditions of containment; unforeseen effects, however, may occur as the result of genetic manipulation. the U.S., experimental protocols for the use of somatic cell gene therapy are reviewed by both the National Institutes of Health (NIH) and the Food and Drug Administration (FDA). The FDA has already approved human drugs and vaccines, diagnostic devices, and food processing enzymes produced through recombinant DNA technology, and is overseeing the generation of genetically engineered food crops. The U.S. Department of Agriculture (USDA) regulates use of genetically engineered plants, microorganisms, and veterinary biological products. B.C.C. For further information on this topic, see ~Biblio. Branches and schools of philosophy , ~Biblio. Genetics . ACIDS, complex molecules produced by living cells and viruses. Their name comes from their initial isolation from the nuclei of living cells. Certain nucleic acids, however, are found not in the cell nucleus but in cell cytoplasm. Nucleic acids have at least two functions: to pass on hereditary characteristics from one generation to the next, and to trigger the manufacture of specific proteins. How nucleic acids accomplish these functions is the object of some of the most intense and promising research currently under way. The nucleic acids are the fundamental substances of living things, believed by researchers to have first been formed about 3 billion years ago, when the most elementary forms of life began on earth. The origin of the so-called genetic code they carry has been accepted by researchers as being very close in time to the origin of life itself ( see Evolution ; Genetics ). Biochemists have succeeded in deciphering the code, that is, determining how the sequence of nucleic acids dictates the structure of proteins. two classes of nucleic acids are the deoxyribonucleic acids (DNA) and the ribonucleic acids (RNA). The backbones of both DNA and RNA molecules are shaped like helical strands. Their molecular weights ( see Molecule ) are in the millions. To the backbones are connected a great number of smaller molecules (side groups) of four different types ( see Amino Acids ). The sequence of these molecules on the strand determines the code of the particular nucleic acid. This code, in turn, signals the cell how to reproduce either a duplicate of itself or the proteins it requires for survival. living cells contain the genetic material DNA. The cells of bacteria may have but one strand of DNA, but such a strand contains all the information needed by the cell in order to reproduce an identical offspring. The cells of mammals contain scores of DNA strands grouped together in chromosomes. In short, the structure of a DNA molecule or combination of DNA molecules determines the shape, form, and function of the offspring. Some viruses, called retroviruses, contain only RNA rather than DNA, but viruses in themselves are generally not considered true living organisms ( see Virus ). pioneering research that revealed the general structure of DNA was performed by the British biophysicists Francis Crick and Maurice Wilkins and by the American biochemist James Dewey Watson. Using an X-ray diffraction picture of the DNA molecule obtained by Wilkins in 1951, Crick and Watson were able to construct (1953) a model of the DNA molecule. For their work, the three scientists received the 1962 Nobel Prize in physiology or medicine. The American biochemist Arthur Kornberg synthesized DNA from "off-the-shelf" substances, for which he was awarded, with the American biochemist Severo Ochoa (for research on RNA), the 1959 Nobel Prize in physiology or medicine. The DNA that he synthesized, although structurally similar to natural DNA, was not biologically active. In 1967, however, Kornberg and a team of researchers at Stanford University succeeded in producing biologically active DNA from relatively simple chemicals. kinds of RNA have a slightly different function from that of DNA. They take

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