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.

Question

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?

Answer 1

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.