Describe Frederick Griffith`s experiment on Streptococcus pneumoniae. Discuss the conclusion he arrived at.
Answers
Answer:
Griffith observed two strains of Streptococcus pneumoniae - smooth shiny colony called S type - virulent with capsule, The other R type rough colony non virulent.
Experiment :
Live S type ---->injected into mice —>mice died.
Live R type —> injected into mice ----> no infection.
Heat killed S type ----> injected into mice ----> no infection.
Heat killed S type + Live R type ----> injected into mice ---->mice died.
S type bacteria were isolated from the dead mice.
Griffith concluded that the genetic material of heat killed S type could transform R type into virulent S type.
He concluded that ‘R’ strain bacteria had been transformed by the heat - killed ‘S’ strain bacteria
Frederick grew streptococcus pneumoniae in a culture dish & observed 2 colonies of strain.- S strain (shiny colonies due to the presence of polysaccchride coat) (virulent) & R strain (non virulent).
◇AIM- To determine the genetic material.
☆Procedure:
1. S strain----> injected to mice ----> mice died
2. R strain----> injected to mice----> mice lives
3. S heat killed strain----> injected to mice---> mice lived
3. S heat killed + R strain (in living state)----> injected to mice----> mice died.
Further he found out living S strain from the dead mice. So , HE concluded that:----- Some transforming material had transferred from heat killed S strain to R strain which enabled the R strain to synthesise a smooth polysaccharide coat and become virulent. However, he was not able to determine that material and nor its biochemical nature.
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