Question

Among the following, identify the correct option that does not show transformation of R strain into S strain?

• A. S strain (heat killed) + R strain (live)
• B. S strain (heat killed) + R strain (live) + Protease
• C. S strain (heat killed) + R strain (live) + RNase
• D. S strain (heat killed) + R strain (live) + DNase

Answer 1

The correct option is D S strain (heat killed) + R strain (live) + DNase

Transformation is uptake of genetic material by bacteria from the surrounding environment.

Avery, MacLeod and McCarty did experiments to determine the biochemical nature of the transforming principle. They purified biochemicals from the heat killed S strain. They added live R strain to the culture of purified biochemicals of the S strain. Transformation of R strain into S strain occurred in the culture containing heat killed S strain + R strain, heat killed S strain + R strain + Protease and heat killed S strain + R strain + RNase.

Protease and RNase degrade proteins and RNA respectively but that did not affect the transformation. Hence proteins and RNA are not transforming principles.

Transformation of R into S strain did not occur in the culture containing heat killed S strain + R strain + DNase. DNase enzyme degrades the DNA and hence it is indicated that DNA is the transforming principle.