The discovery of DNA and its structure

... The discovery of DNA and its structure Evidence for DNA as the genetic code The discovery of transformation by Griffith in 1928 started them idea that genetic material is nucleic acid. The bacterium Pneumococcus kills mice by causing pneumonia. The virulence of the bacterium is determined by the capsular polysaccharide, a component of the cell surface that allows the bacterium to escape destruction by the host. Several types (I, II, III) of the Pneumococcus have different capsular polysaccharides, which have a smooth appearance. Each of the smooth Pneumococcal types can give rise to variants that fail to produce the capsular polysaccharide. These bacteria have a rough surface. They are avirulent; they do not kill the mice, because the lack of the polysaccharide capsule allows the animal to destroy the bacteria. When smooth bacteria are killed by heat treatment, they lose their ability to harm the animal. But inactive heat-killed S bacteria and the

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