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:
A. To demonstrate that the transforming factor is an enzyme
B. To demonstrate that the transforming factor is not a protein
C. To destroy nucleic acids in the extract
D. To destroy any capsules in the extract
E. To prevent the extract from being contaminated by nonencapsulated bacteria