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Question : Define transformation in Griffith's experiment. Discuss how it helps in the identification of DNA as the genetic material. |
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Answer» Solution :In 1928, Frederick Griffith, in a series of experiments with Streptococcus pneumoniae (bacterium responsible for pneumonia), WITNESSED a miraculous transformation, in the bacteria. During the course of his experiment, a living organism (bacteria) had changed in physical form. When Streptococcus pneumoniae (pneumococcus) bacteria are grown on a culture PLATE, some produce smooth shiny colonies (S) while others produce rough colonies (R). This is because the S strain bacteria have a mucous (polysaccharide) coat, while R strain does not. Mice infected with the S strain (virulent) die from pneumonia infection but mice infected with the R strain do not develop pneumonia. S strain INJECT into mice `rarr` Mice die R strain `rarr`Inject into mice `rarr` Mice LIVE Griffith was able to kill bacteria by heating them. He observed that heat- killed S strain bacteria injected into mice did not kill them. S strain (heat killed) `rarr`Inject into mice `rarr`Mice live `rarr`When he injected a mixture of heat-killed S and live R bacteria, the mice died. Moreover, he recovered living S bacteria from the dead mice. `rarr` S strain (heat killed ) + `rarr` Inject into mice `rarr` Mice die R strain (live) `rarr` He concluded that the R strain bacteria had somehow been transformed by the heat-killed S strain bacteria. Some .transforming principle., transferred from the heat-killed S strain, had enabled the R strain to synthesise a smooth polysaccharide coat and become virulent. This must be due to the transfer of the genetic material. However, the BIOCHEMICAL nature of genetic material was not defined from his experiments. |
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