In the 1940’s, Avery, MacCleod, and McCarty transformed nonencapsulated bacteria into encapsulated forms by growing the nonencapsulated cells in a cultre containing an extract made from dead encapsulated cells.  The transformed cells produced colonies of encapsulated bacteria.  Three different procedures and their results are outlined below.

Procedure I:
Extract made from dead encapsulated cells added to culture medium.
Nonencapsulated bacteria added to culture medium.

Results:  Both nonencapsulated and encapsulated bacteria grow.

Procedure II:
Extract made from dead encapsulated cells treated with protein-degrading enzymes before adding extract to culture medium.
Nonencapsulated bacteria added to culture medium.

Results:  Both nonencapsulated and encapsulated bacteria grow.

Procedure III:

Extract made from dead encapsulated cells treated with DNAse (an enzyme that selectively destroys DNA) before adding extract to culture medium.
Nonencapsulated bacteria added to culture medium.

Results:  Only nonencapsulated bacteria grow.

What was the purpose of treating the extract with protein-degrading enzymes in Procedure II?

Answers:
To demonstrate that the transforming factor is an enzyme

To demonstrate that the transforming factor is not a protein *CORRECT*

To destroy nucleic acids in the extract

To destroy any capsules in the extract

To prevent the extract from being contaminated by nonencapsulated bacteria

can someone explain why the correct answer is correct?

The purpose of treating the extract with protein-degrading enzymes in Procedure II was to demonstrate that the transforming factor was not a protein. By treating the extract with protein-degrading enzymes, any proteins present in the extract would be destroyed, while other molecules such as nucleic acids would remain intact. If the transforming factor was a protein, then the treated extract would not be able to transform the nonencapsulated bacteria into encapsulated forms. However, since the treated extract was still able to transform the nonencapsulated bacteria, this demonstrated that the transforming factor was not a protein.

The purpose of treating the extract with protein-degrading enzymes in Procedure II was to demonstrate that the transforming factor is not a protein. This is the correct answer because, in Procedure II, both nonencapsulated and encapsulated bacteria still grew despite the protein-degrading enzymes being added to the extract.

If the transforming factor was a protein, it would have been degraded by the protein-degrading enzymes, resulting in the loss of its ability to transform the nonencapsulated bacteria into encapsulated forms. However, since both types of bacteria still grew, it suggests that the transforming factor is not a protein. This finding supports the conclusion that the transforming factor is most likely a nucleic acid, which was further supported by the results of Procedure III, where only the nonencapsulated bacteria grew after the extract was treated with DNAse.

The correct answer is "To demonstrate that the transforming factor is not a protein". This is because in Procedure II, the extract made from dead encapsulated cells was treated with protein-degrading enzymes. By treating the extract with protein-degrading enzymes and then adding it to the culture medium along with nonencapsulated bacteria, and observing that both nonencapsulated and encapsulated bacteria still grew, it effectively demonstrates that the transforming factor responsible for the transformation of nonencapsulated bacteria into encapsulated forms is not a protein.

If the transforming factor were a protein, the protein-degrading enzymes would have broken it down and inactivated it, rendering it unable to transform the nonencapsulated bacteria. However, if both nonencapsulated and encapsulated bacteria still grew in the presence of the treated extract, it indicates that the transforming factor is not a protein and is likely something else, such as nucleic acids.

Therefore, by using Procedure II and observing the growth of both nonencapsulated and encapsulated bacteria, it can be concluded that the transforming factor is not a protein. This experiment helps to narrow down and understand the nature of the substance responsible for the transformation process.