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Question : Describe Transforming Principle. |
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Answer» Solution :Transforming Principle : In 1928, Frederick GRIFFITH, in a series of experiment 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 produced 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 strain (virulent) DIE from pneumonia infection but mice infected with the R strain do not develop pneumonia. `"S strain "rarr" 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 "` `"S strain (heat killed) "+ "R strain (live) "rarr" Inject into mice "rarr" mice die "` 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. 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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