Explain Griffith ‘s experiments on mice and infection of Diplococcus pneumoniae.
Explain Griffith ‘s experiments on mice and infection of Diplococcus pneumoniae.
The transformation experiments conducted by Frederick Griffith in 1928 are of great importance in establishing the nature of genetic material.
He used two strains of bacterium Diplococcus or Streptococcus pneumoniae or pneumococcus, i.e., S-III and R-II.
a. Smooth (S) or capsulated type: These have a mucous coat and produce shiny colonies. These bacteria are virulent and cause pneumonia.
b. Rough (R) or non-capsulated type: Mucous coat is absent and these produce rough colonies. These bacteria are non-virulent and do not cause pneumonia. The experiment can be described in the following four steps:
i) Smooth-type bacteria were injected into mice. The mice died as a result of pneumonia caused by bacteria.
ii) Rough-type bacteria were injected into mice. The mice lived and pneumonia did not occur.
iii) Smooth-type bacteria, which normally cause disease, were heat-killed and then injected into mice. The mice lived and pneumonia was not caused.
iv) Rough-type bacteria (living) and smooth-type heat killed bacteria (both known not to cause disease) were injected together into mice. The mice died due to pneumonia and virulent smooth-type living bacteria could also be recovered from their dead bodies.
From the fourth step of the experiment, he concluded that some rough-type bacteria (non-virulent) were transformed into smooth-type bacteria (virulent).
This occurred perhaps due to the absorption of some transforming substance by rough-type bacteria from heat-killed smooth-type bacteria.
This transforming substance from smooth-type bacteria caused the synthesis of capsule which resulted in the production of pneumonia and the death of mice.
Therefore, transforming principle appears to control genetic characters (e.g., capsule, as in this case). However, the biochemical nature of genetic material was not defined from his experiments.
The transformation experiments conducted by Frederick Griffith in 1928 are of great importance in establishing the nature of genetic material.
He used two strains of bacterium Diplococcus or Streptococcus pneumoniae or pneumococcus, i.e., S-III and R-II.
a. Smooth (S) or capsulated type: These have a mucous coat and produce shiny colonies. These bacteria are virulent and cause pneumonia.
b. Rough (R) or non-capsulated type: Mucous coat is absent and these produce rough colonies. These bacteria are non-virulent and do not cause pneumonia. The experiment can be described in the following four steps:
i) Smooth-type bacteria were injected into mice. The mice died as a result of pneumonia caused by bacteria.
ii) Rough-type bacteria were injected into mice. The mice lived and pneumonia did not occur.
iii) Smooth-type bacteria, which normally cause disease, were heat-killed and then injected into mice. The mice lived and pneumonia was not caused.
iv) Rough-type bacteria (living) and smooth-type heat killed bacteria (both known not to cause disease) were injected together into mice. The mice died due to pneumonia and virulent smooth-type living bacteria could also be recovered from their dead bodies.
From the fourth step of the experiment, he concluded that some rough-type bacteria (non-virulent) were transformed into smooth-type bacteria (virulent).
This occurred perhaps due to the absorption of some transforming substance by rough-type bacteria from heat-killed smooth-type bacteria.
This transforming substance from smooth-type bacteria caused the synthesis of capsule which resulted in the production of pneumonia and the death of mice.
Therefore, transforming principle appears to control genetic characters (e.g., capsule, as in this case). However, the biochemical nature of genetic material was not defined from his experiments.
