Question

When Avery and his colleagues had obtained what was concluded to be the transforming factor from the IIIS virulent cells, they treated the fraction with proteases, RNase, and DNase, followed in each case by the assay for retention or loss of transforming ability. What were the purpose and results of these experiments? What conclusions were drawn?

Answer 1

Answer:

The fraction was treated with proteases and RNase to remove the contamination of protein and RNA respectively from the DNA sample.

Conclusion: DNA is the genetic material and is responsible for transformation. RNA and protein are not responsible for transformation.

Explanation:

Avery and his colleagues extracted the DNA from the heart killed virulent strains of bacterium Streptococcus pneumoniae. They showed that the DNA from the heat-killed virulent strains of the bacteria was able to transform the live nonvirulent strains into the virulent form.

There was a possibility of the presence of RNA or protein along with the extracted DNA. So, the RNA or protein could serve as a transforming factor but not the DNA.  

To exclude the possibility of RNA or protein to serve as heredity material, they treated the extract from the heat-killed virulent strains with DNase, RNase and proteases separately.

It was shown that the extract treated with RNase or protease was able to bring about transformation while the extract treated with DNase could not transform the nonvirulent strains.

Hence, it was concluded that DNA was the genetic material and the molecule responsible for transformation.