Реферат: Linus Pauling The Father Of Genetics Essay

Linus Pauling, The Father Of Genetics Essay, Research Paper

[ABSTRACT]AbstractIn the late 1940s, few Americans had any idea what the long-term effects of nuclear radiation might be, and their government wasn’t telling them. Dr. Linus Pauling had already won renown for his application of modern physics to the problems of chemistry when he took on the unpopular task of informing the public about the dangers of nuclear weapons. Pauling endured exclusion and ridicule for his firm stand, but went on to win two Nobel Prizes: the 1954 award for Chemistry and the 1962 Nobel Peace Prize for his efforts to end the open-air testing of nuclear weapons. To the end of his 93 years, Linus Pauling devoted himself to the cause of world peace, to the struggle against disease, and to educating the public about a multitude of health issues, from the hazards of smoking to the benefits of vitamin C. Pauling’s work as a chemist would have been sufficient to earn him an honored place in the history of science, but his humanitarian efforts made him a beloved figure around the world. [BODY] “A couple of days after my talk, there was a man in my office from the FBI saying – Who told you how much plutonium there is in an atomic bomb? And I said – Nobody told me, I figured it out.” -Linus Pauling Like Michael Faraday, Linus Pauling was born poor. He struggled at menial jobs to support himself at high school, while studying for a degree in chemical engineering at the Oregon Agricultural College. All the same, he became interested in the electron theory of valence when he was only eighteen, and after this he “continued to hope that the empirical information about the properties of substances could eventually be encompassed in a theory of the structure of molecules”. Fulfillment of his hope began to take shape in 1926 when he spent a postdoctoral year at Munich with Germany’s greatest teacher of theoretical physics, Arnold Sommerfeld, just as Erwin Schr dinger published his first papers on wave mechanics. Sommerfeld immediately recognized their importance and gave a course of lectures on them. Having absorbed what knowledge he could in Munich, Pauling next went to Z rich to work with Schr dinger himself, but found his stay disappointing, because Schr dinger liked to work all by himself and didn t take much notice of him. Pauling then returned to California Institute of Technology at Pasadena where he had taken his doctoral degree and started his work on the nature of the chemical bond.In a later paper Pauling applied to chemistry the concept of resonance originally introduced by Heisenberg into quantum mechanics. “It is found that there are many substances whose properties cannot be accounted for by means of a single electronic structure of the valence bond type, but which can be fitted into the scheme of classical valence theory by the consideration of resonance among two or more structures”. Benzene was the prime example.Pauling’s valence bond theory established the relationship between interatomic distances, mostly derived from accurate crystallographic data, and bond energies, on which much of his successful interpretation of the chemical properties of organic compounds was based. With that in mind, he founded at Pasadena an outstanding research school of structural chemistry. Pauling’s Munich experience also led him to write an Introduction to Quantum Mechanics for chemists together with E. Bright Wilson, which was first published in 1935 and remains a useful historic masterpiece.In 1949 someone got Pauling interested in sickle cell disease, a genetic disorder affecting mainly blacks which causes the red cells to be distorted to various sickled shapes on loss of oxygen. Pauling suggested to his young collaborators Itano, Singer and Wells that they should examine the electrophoretic mobilities of normal and sickle cell hemoglobin. They found them to be different, because sickle cell hemoglobin carries two fewer negative charges than normal hemoglobin. Pauling published this result in science under the dramatic title: “Sickle cell hemoglobin, a molecular disease”.Among biochemists, Pauling is most famous for his discovery of the alpha-helix which came as the culmination of X-ray analyses of the structures of amino acids pioneered in the 1930s and ’40s by his collaborators Robert Corey and Edward Hughes; at that time glycine, alanine and diketopiperazine presented a degree of complexity that carried X-ray analysis to the very limits. The results provided Pauling with the data he needed for the interpretation of the X-ray diffraction patterns which Bill Astbury at Leeds had obtained from protein fibers such as hair, nails or muscle. Pauling argued that in a long chain polymer made of chemically equivalent units, all units must occupy geometrically equivalent positions, which was possible only in a helix. Further, the structure of diketopiperazine had shown that the peptide bond had partial double bond character, so that the atoms must all lie in a plane. Finally, all NH groups should form hydrogen bonds with COs. Lying in bed with the flu in Oxford in 1948, Pauling amused himself by building a paper chain of planar peptides and found a satisfactory structure by folding them into a helix with 3.6 residues per turn. Shortly after this he visited Kendrew and me in Cambridge. It helped to earn him the Nobel Prize in Chemistry in 1954, but he had really deserved it for his many other outstanding contributions to chemistry much earlier.

In the same year, 1948, Pauling made another important prediction: “I think that enzymes are molecules that are complementary in structure to the activated complexes of the reactions that they catalyze, that is, the molecular configuration that is intermediate between the reacting substances and the products of the reaction”.After the alpha-helix Pauling produced one more fundamental paper. When the amino acid sequences of the hemoglobins of different animals were beginning to be known, it became clear that the number of amino acid substitutions increased with the distance between species on the evolutionary tree. This inspired Pauling and his young collaborator Emile Zuckerkandl to propose the existence of an evolutionary clock which ticks at the rate of about one amino acid substitution per hundred residues per 5 million years. Like many of Pauling’s papers this one initiated an entire new field of research which has since occupied many other scientists’ lives. Pauling continued publishing papers almost to the end of his life, but nothing as fundamental as his earlier work appeared, possibly because he became too preoccupied, first with the threat of nuclear war and later with vitamin C.Pauling’s anti-nuclear stance earned him the reputation of a “red”. In 1952, when the Royal Society organized a Discussion on the Structure of Proteins at which Pauling should have been the principal contributor, he could not come because the State Department had withdrawn his passport. In 1954, the English philosopher Bertrand Russell gave Christmas lectures on the radio warning of the dangers of nuclear war. Next year he drew up a manifesto against nuclear arms which Albert Einstein signed a few days before his death. This concluded with the words: “There lies before us, if we choose, continual progress in happiness, knowledge and wisdom. Shall we, instead, choose death, because we cannot forget our quarrels? We appeal, as human beings, to human beings: remember your humanity and forget the rest. If you can do so, the way lies open to a new paradise; if you cannot, there lies before you the risk of universal death”. Pauling signed this manifesto together with seven prominent physicists and the geneticist Hermann Muller; it led to the convening of the first Pugwash Conference at which Soviet and Western scientists discussed measures to reduce the dangers of nuclear war. In 1958, Pauling published a book: No More War and handed to Dag Hammarskj ld, the Secretary General of the United Nations, a petition signed by 9,235 scientists “urging that an international agreement to stop the testing of nuclear weapons be made now in as much as it is the scientists who have some measure of the complex factors involved in the problem, such as the magnitude of the genetic and somatic effects of the released radioactive materials”. In May 1961 Pauling organized a conference of forty scientists on nuclear disarmament in Oslo, and afterwards led hundreds of people in a torchlight procession against nuclear war through the streets of Oslo. His campaign, made a vital contribution to the conclusion of the atmospheric test ban in 1963 and won him the Nobel Prize for Peace in December of that year. He also campaigned against the war in Vietnam, undeterred by being called a traitor.In 1966 Pauling conceived the idea that huge doses of vitamin C were vital for health, and that they cured the common cold and even cancer. Chemists shops in Britain still sell vitamin C as “Linus Powder”, of which he swallowed about eighteen grams every day; probably about 100 milligrams would have been absorbed and the rest excreted. Ascorbic acid is a scavenger of free radicals and a deficiency of it may increase the likelihood of cancer, but there is no solid evidence that such massive doses have any preventative effect.Pauling’s fundamental contributions to chemistry cover a tremendous range, and their influence on generations of young chemists was enormous. In the years between 1930 and 1940 he helped to transform chemistry from a largely phenomenological subject to one based firmly on structural and quantum mechanical principles. In later years the valence bond and resonance theories which formed the theoretical backbone of Pauling’s work were enhanced by R.S. Mulliken’s molecular orbital theory which provided a deeper understanding of chemical bonding. For instance, it allowed C. Longuet-Higgins and W. Lipscomb to predict and explain the structures of the boranes, which would not have been possible on the basis of Pauling’s concepts. Pauling’s combination of encyclopedic knowledge of chemistry and imaginative insight was unique; many people regard him as the greatest chemist of the century.