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?

Verified step by step guidance

1. Step 1: Understand the context of Avery's experiment, which aimed to identify the 'transforming factor' responsible for transferring genetic information from virulent IIIS cells to non-virulent IIR cells, causing transformation.
2. Step 2: Recognize that Avery and colleagues treated the purified transforming material with three different enzymes: proteases (which degrade proteins), RNase (which degrades RNA), and DNase (which degrades DNA), to determine which type of molecule was responsible for transformation.
3. Step 3: Analyze the purpose of each treatment: proteases tested if proteins were the transforming factor, RNase tested if RNA was responsible, and DNase tested if DNA was the transforming molecule.
4. Step 4: Note the results: treatment with proteases and RNase did not abolish the transforming ability, meaning transformation still occurred, whereas treatment with DNase destroyed the transforming ability, indicating that DNA was necessary for transformation.
5. Step 5: Conclude that the transforming factor was DNA, as only DNase treatment eliminated the ability to transform non-virulent cells, providing strong evidence that DNA carries genetic information.

Key Concepts

Transforming Principle

The transforming principle refers to the substance responsible for transferring genetic information from one bacterial strain to another, as demonstrated in Griffith's experiment. Avery and colleagues aimed to identify this factor by isolating it from virulent IIIS cells and testing its ability to transform non-virulent bacteria.

Enzymatic Treatment to Identify Macromolecules

Proteases, RNase, and DNase are enzymes that degrade proteins, RNA, and DNA respectively. By treating the transforming factor with these enzymes, Avery's team tested which macromolecule was essential for transformation, observing whether the ability to transform bacteria was lost after each treatment.

DNA as the Genetic Material

The experiments showed that only DNase treatment destroyed the transforming ability, indicating DNA was the transforming factor. This provided strong evidence that DNA, not protein or RNA, carries genetic information, a foundational discovery in molecular genetics.