(a) How did Griffith demonstrate transforming principle in Genetics?(b) How was the biochemical characterisation of the above mentioned principle proved to a certain extent following Griffith?
Answers
The two scientists that proove DNA is the genetic material are:
(i) Griffith Transformation Experiment
(a) In 1928, Frederick Griffith, in a series of experiments with Streptococcus pneumoniae (bacterium responsible for pneumonia), witnessed a miraculous transformation in the bacteria.
(b) 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 ----> Mice die
R strain ----> Inject into mice ----> Mice live
Griffith was able to kill bacteria by heating them. He observed that heatkilled S strain bacteria injected into mice did not kill them.
S strain (heat-killed) ----> Inject into mice ----> Mice live
When he injected a mixture of heat-killed S and live R bacteria, the mice died.
S strain (heat-killed) + R strain (live) ----> Inject into mice ----> Mice die
Moreover, he recovered living S bacteria from the dead mice.