Question

Define transformation in Griffith's experiment. Discuss how it helps in the identification of DNA as the genetic material.

Answer 1

Transformation:

The change in the DNA of an organism by picking up the DNA from the dead organism or environment is referred to as the transformation in Griffith's experiment.

• The smooth (S) strain of Streptococcus pneumoniae is virulent and the rough (R) strain is non-virulent.
• When the S strain was injected into the mouse it died but when the R strain was injected it lived.
• When the heat killed S strain alone injected into the mouse it lived.
• But when the R strain along with the heat killed S strain were injected together the mouse died.
• This is because the R strain has acquired some transforming principle from heat killed S strain and transformed into a virulent strain. This is known as transformation.
• But the chemical nature of the transforming principle was unknown.
• After this experiment Avery, MacLeod and McCarty purified proteins, DNA and RNA from heat killed S strain. They discovered that only DNA could transform the R strain into S strain.
• They also found that presence of protease and RNase does not have any effect on the transformation, but presence of DNase inhibited it.
• Thus DNA was identified as genetic material.