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?

Short answer

Answer: The main conclusion drawn by Avery and his colleagues from their experiment was that DNA is the molecule responsible for the transforming ability of the virulent cells, and it carries the genetic information which can influence the properties of the bacteria, such as virulence. This was determined by the fact that after treating the sample with DNase, the fraction lost its transforming ability, while treatment with proteases and RNase did not affect the transforming ability.

Step-by-step solution

Understanding the Experiment

Avery and his colleagues wanted to identify the transforming factor from the IIIS virulent cells, which is the substance responsible for transforming a non-virulent bacterium into a virulent one. They treated the extracted fraction containing the potential transforming factors with proteases, RNase, and DNase. After each treatment, they tested the ability of the fraction to retain its transforming ability or lose it.

Purpose of the Treatments

The purpose of these treatments was to help Avery and his colleagues identify which type of molecule was responsible for the transforming ability. By treating the fractions with each of these enzymes selectively, they can eliminate specific types of molecules: - Proteases break down proteins. - RNase degrades RNA. - DNase degrades DNA.

Results of the Treatments

After treating the fraction with proteases, the fraction still retained its transforming ability, suggesting that proteins were not the transforming factor. After treatment with RNase, the fraction also maintained its transforming ability, indicating that RNA was not the transforming factor. However, after treating the sample with DNase, the fraction lost its transforming ability, suggesting that DNA had been the transforming factor.

Conclusions Drawn

From the results of these treatments, Avery and his colleagues concluded that the molecule responsible for the transforming ability of the virulent cells was DNA, not proteins or RNA. This finding led them to infer that DNA carries the genetic information which can influence the properties of the bacteria, such as virulence. The discovery helped to establish the role of DNA as the carrier of genetic information and laid the foundation for further studies on molecular genetics.