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The discovery of DNA The structure of nucleic acids was discovered in the C19. Later it was found that the sugar in nucleic acid could be either ribose (RNA) or deoxyribose (DNA). In 1943, [Oswald Avery]? proved that DNA carries genetic information and suggested DNA might actually be the gene. In 1948, [Linus Pauling]? discovered that many proteins take the shape of an alpha helix. In 1950, biochemist [Erwin Chargaff]? found that the arrangement of bases in DNA varied, but the amount of certain bases always occured in a one-to-one ratio. In England two seperate investigations into DNA took place in the 1950s. At Cambridge University, Francis Crick and James Watson were making physical models to eventually create an accurate picture of the molecule. At [Kings College]? in London, [Maurice Wilkins]? and [Rosalind Franklin]? were examing X-ray diffraction images of DNA. In 1951, Watson attended a lecture by Franklin on her work to date. She had found that DNA can exist in two forms. From this she had deduced that the phosphate part of the molecule was on the outside. Based on a imperfect recollection of her information, Watson and Crick made a failed model. Franklin had also found that the X-ray diffractions of one of the forms of DNA had the characteristics of a helix. She suspected that DNA was helical but did not announce this. Watson and Crick made a crucial step, suggesting the molecule was made of two nucleotide chains, each in a helix as Franklin had found, but one going up and the other going down. Crick learned of the work of Chargaff in 1952. He added that to the model, so that matching base pairs interlocked to keep the distance between the chains constant. This model showed that each strand of the DNA molecule was a template for the other. The fit with experimental data was such that it was almost immediately accepted. Their paper 'A structure for Deoxyribose Nucleic Acid' was published in April 1953. further research uncovered how DNa made proteins in 1957. In 1962, Watson, Crick, and Wilkins won the Nobel Prize for physiology/medicine, Franklin had died. |
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