Question

DNA experiment

What was Fredrick Griffith’s experiment and how was it relevant?

Diagram the experiment in detail.

Answer 1

Answer -

Fredrick grifith conducted a series of experiments in the year 1928 with Streptococcus pneumoniae bacteria .

On growing Str. Pneumoniae bacteria in a culture plate , some bacteria grew smooth colonies and some grew though colonies on the plate. He identified that the S strain bacteria produced smooth shiny colonies as it contained mucopollysaccharide coat . And the R stain bacteria produced rough colonies.

Also mice when infected with S strain bacteria would die of penumoniae and mice injected with R strain would not die .

So fredrick frifith , heat killed few strains of bacteria.

He observed that heat killed S strain bacteria did not cause pneumoniae or kill the mice .

Then he injected a mixed cuture of S and R strain Str, pneumoniae into the mice and the mice died and on autopsy live S strain bacteria were recovered from the dead mice.

This lead Grifith to the colclusion that R strain bacteria had somehow transformed by the heat killed S strain bacteria. He further concluded there was a transforming principle transferred from S strained bacteria to R strain bacteria that enabled it to synthesise mucopolysaccharide coat and becomw virulent.

He speculated that the transforming orinciple must have been the genetic material , but the chemical nature if it was not understood or known at that time .

The experiment was relevant as it provided the conclusion of a transforming principle which was responsible for exchange of genome between the bacteria . The transforming principle was later extensively researched by avery , Mc leod and macarthy and proved to be DNA.

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