Linus Pauling

Linus Carl Pauling (February 28, 1901 – August 19, 1994) was an American physical chemist, widely regarded as the premier chemist of the twentieth century. Pauling was a pioneer in the application of quantum mechanics to chemistry, and in 1954 was awarded the Nobel Prize in chemistry for his work describing the nature of chemical bonds. He also made important contributions to crystal and protein structure determination, and was one of the founders of molecular biology. Pauling received the Nobel Peace Prize in 1962 for his campaign against above-ground nuclear testing, becoming the only person in history to individually receive two Nobel Prizes (Marie Curie won Nobel Prizes in physics and chemistry, but shared the former and won the latter individually; John Bardeen won two Nobel Prizes, but both were in the field of physics, and both were shared; Frederick Sanger won two Nobel Prizes in chemistry, but one was shared). Later in life, he became an advocate for regular consumption of massive doses of Vitamin C, a regimen now regarded as medically unorthodox.

Work on biological molecules

In the mid-1930s, Pauling decided to strike out into new areas of interest. Early in his career, he had mentioned a lack of interest in studying molecules of biological importance. But as Caltech was developing a new strength in biology, and Pauling interacted with such great biologists as Thomas Hunt Morgan, Theodosius Dobzhanski, Calvin Bridges, and Alfred Sturtevant, he started to become interested in studying biological molecules. His first work in this area involved the structure of hemoglobin. He was able to demonstrate that the hemoglobin molecule changes structure when it gains or loses an oxygen atom. As a result of this observation, he decided to make a more thorough study of protein structure in general. He returned to his earlier use of X-ray diffraction analysis. But protein structures were far less amenable to this technique than the crystalline minerals of his former work. The best X-ray pictures of proteins in the 1930s had been made by the British crystallographer William Astbury, but when Pauling tried, in 1937, to account for Astbury's observations quantum mechanically, he could not.

Related Topics:
Biological - Thomas Hunt Morgan - Theodosius Dobzhanski - Calvin Bridges - Alfred Sturtevant - Hemoglobin - Oxygen - Protein - X-ray diffraction - Crystal - Mineral - Crystallographer - William Astbury - 1937 - Quantum mechanically

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It took eleven years for Pauling to explain the problem: his mathematical analysis was correct, but Astbury's pictures were taken in such a way that the protein molecules were tilted from their expected positions. Pauling had formulated a model for the structure of hemoglobin in which atoms were arranged in a helical pattern, and applied this idea to proteins in general.

Related Topics:
Mathematical - Helical

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In 1951, based on the structures of amino acids and peptides and the planarity of the peptide bond, Pauling and colleagues correctly proposed the alpha helix and beta sheet as the primary structural motifs in protein secondary structure. This work exemplified his ability to think unconventionally; central to the structure was the unorthodox assumption that one turn of the helix may well contain a non-integral number of amino acid residues.

Related Topics:
Alpha helix - Beta sheet - Secondary structure

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Pauling then suggested a helical structure for deoxyribonucleic acid DNA but in this structure he uncharacteristically made several basic mistakes. Sir Lawrence Bragg had been disappointed that Pauling had won the race to find the alpha helix. Bragg's team had made a fundamental error in making their models of protein; not recognizing the planar nature of the peptide bond. When it was learned at the Cavendish Laboratory that Pauling was working on molecular models of the structure of DNA, Watson and Crick were allowed to make a molecular model of DNA using unpublished data from Maurice Wilkins and Rosalind Franklin at King's College. Early in 1953 James D. Watson and Francis Crick propose a correct structure for the DNA double helix. One of the impediments facing Pauling in this work was that he did not have access to the high quality X-ray diffraction photographs of DNA taken by Rosalind Franklin, which Watson and Crick had seen. He planned to attend a conference in England, where he might have been shown the photos, but he could not do so because his passport was withheld at the time by the State Department, on suspicions that he had Communist sympathies. This was at the start of the McCarthy period in the United States.

Related Topics:
Deoxyribonucleic acid - DNA - Sir Lawrence Bragg - Cavendish Laboratory - Maurice Wilkins - Rosalind Franklin - King's College - James D. Watson - Francis Crick - McCarthy

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Pauling also studied enzyme reactions and was among the first ones to point out that enzymes bring about reactions by stabilizing the transition state of the reaction, a view which is central to understanding their mechanism of action. He was also among the first scientists to postulate that the binding of antibodies to antigens would be due to a complementarity between their structures. Along the same lines, with the physicist turned biologist Max Delbruck, he wrote an early paper arguing that genetic replication was likely to be due to complementarity, rather than similarity, as suggested by a few researchers. This was made clear in the model of the structure of DNA that Watson and Crick discovered.

Related Topics:
Enzyme - Antibodies - Max Delbruck

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