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, ribonuclease, and deoxyribonuclease, followed 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 purpose of treating the fraction with proteases, ribonuclease, and deoxyribonuclease in Avery and his colleagues' experiments was to determine the nature of the transforming factor. This allowed them to deduce which type of molecule was responsible for the transformation. From the experiments, they concluded that the transforming factor in the virulent IIIS cells was DNA, as the transforming ability was lost when treated with deoxyribonuclease, providing significant evidence that DNA carries genetic information in living organisms.

Step-by-step solution

Understanding the experiments

To identify the transforming factor in the virulent IIIS cells, Avery and his colleagues performed a series of experiments. They treated the fraction, which was thought to contain the transforming factor, with proteases, ribonuclease, and deoxyribonuclease. Then, they assayed the treated fraction for the retention or loss of transforming ability.

Explaining the purpose of treating the fraction with different enzymes

The purpose of treating the fraction with proteases, ribonuclease, and deoxyribonuclease was to determine the nature of the transforming factor. Proteases break down proteins, ribonuclease breaks down RNA molecules, and deoxyribonuclease breaks down DNA molecules. By treating the fraction with these enzymes and observing the retention or loss of transforming ability, they could deduce which type of molecule was responsible for the transformation.

Discussing the results of the experiments

After the fraction was treated with proteases and ribonuclease, the transforming ability remained, indicating that proteins and RNA were not the transforming factors. However, when the fraction was treated with deoxyribonuclease, the transforming ability was lost. These results showed that the transforming factor was sensitive to deoxyribonuclease, indicating that the transforming factor was most likely DNA.

Concluding the experiments

From the results of these experiments, Avery and his colleagues concluded that the transforming factor in the virulent IIIS cells was DNA. This was a groundbreaking discovery, as it showed that DNA, not proteins or RNA, was responsible for carrying genetic information and could cause the transformation in bacteria. The conclusions of these experiments provided significant evidence to support the understanding of DNA as the genetic material in living organisms.