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The Era Before Watson and Crick.

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Joanna Slusarz Mr. Rock AP Biology November 11, 2003 B.W.&C.-The Era Before Watson and Crick James Watson and Francis Crick are the men attributed with the discovery of DNA's "double helix." However, they based their research on the works of many preceding scientists. It all began in 1865 with Gregor Mendel's garden pea experiments, which revealed the existence of genes and their transfer from one generation to the next. By 1905, it had been learned that within living cells the genes are strung together like beads on the chromosomes, which then copy themselves and separate. But how, no one knew. By the 1920s, it was thought that genes were made of protein. Although DNA (which was identified in 1871 by a young Swiss scientist, Friedrich Miescher), was also a main ingredient in chromosomes, protein, however, was far more interesting to geneticists than DNA because it was in greater abundance, was more complex, and there was a larger variety of it. ...read more.


Published in 1938, the model was to remain constant throughout all the attempts to solve DNA's structure that were to come. However, Astbury made serious errors, his work was uncertain, and he had no clear idea of where to go from there. In 1943, Avery, at 67, was still working at the Rockefeller Institute and experimenting with pneumococcus (bacteria that cause pneumonia). In 1928, he made a revolutionary discovery when he found that when DNA was transferred from a dead strain of pneumoccocus to a living strain, it brought with it the hereditary attributes of the donor. Avery was hesitant about publishing his discovery as he was "not yet convinced that (he had) sufficient evidence." A year later, however, Avery, with two colleagues, wrote out their research. They described an intricate series of experiments using the two forms of pneumococcus, virulent and nonvirulent. ...read more.


The lectures were published as a book the following year. To the molecular biologist and scientific historian Gunther Stent of the University of California at Berkeley, What Is Life? was the Uncle Tom's Cabin of biology-a small book that started a revolution. In 1949, Erwin Chargaff was one of the very few who considered Avery's results and analyzed the proportions of the four bases of DNA. He found a curious correspondence: the numbers of molecules present of the two bases, adenine and guanine, were always equal to the total amount of thymine and cytosine, the other two bases. This ratio, found in all forms of DNA, cried out for explanation, but Chargaff could not think what it might be. That is where Rosalind Franklin arrived at King's College London on January 5, 1951, leaving coal research to work on DNA. She teamed up with James Watson and Francis Crick and the "double helix" theory was born. ...read more.

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