Question

From the experiments carried out by Avery, Macleod, and McCarty by using various enzymes, which of the following results prominently proved that DNA is the transforming material?
A. DNA of heat-killed ‘S’ + R type + DNAase —> a virulent strain
B. DNA of heat-killed ‘S’ + R type + RNAse —> virulent strain
C. DNA of heat-killed ‘S’ + R type —> virulent strain
D. DNA of heat-killed ‘S’ + R type + Protease —> virulent strain

Answer 1

Hint: DNA was earlier named as a transforming principle. Scientists did not know that DNA carried genetic information in 1928, but they actually knew that something could cause bacteria to transform from one type to another.
When a bacterium grabs free-floating DNA and incorporates it into its own genome, transformation occurs. Frederick Griffith discovered the transforming principle during an experiment.

Complete Step by Step Answer:
Oswald Avery, Colin MacLeod, and Maclyn McCarty demonstrated that DNA (rather than proteins) can change the properties of cells, providing insights into the chemical nature of genes.
While researching Streptococcus pneumoniae, a bacteria that can cause pneumonia, Avery, MacLeod, and McCarty discovered DNA as the "transforming principle." The bacteriologists were curious about the difference between two Streptococci strains identified by Frederick Griffith in 1923: the S (smooth) strain, which possesses a polysaccharide coat and generates smooth, shiny colonies on a lab plate, and the R (rough) strain, which lacks the coat and generates colonies that look rough as well as irregular. The R strain is relatively harmless because it lacks an enzyme required to produce the capsule observed in the virulent S strain.
Griffith discovered a way to transform the R strain into the virulent S strain. He injected mice with R strain cells as well as heat-killed S strain cells at the same time, the mice developed pneumonia and ended up dead. Griffith discovered live bacteria of the fatal S type in their blood. The S strain extract had "transformed" the R strain bacteria into S form in some way. Avery and his lab members began a concerted effort in the early 1940s to purify the "transforming principle" as well as understand its chemical nature.
Bacteriologists assumed that the transforming component was a protein. The transforming principle was precipitable with alcohol, indicating that it wasn't a carbohydrate like a polysaccharide coat. However, Avery and McCarty discovered that proteases, which degrade proteins, did not destroy the transforming principle. Lipases, which digest lipids, did not work either. They discovered that the transforming material was high in nucleic acids, but that ribonuclease, which digests RNA, did not deactivate it. They also discovered a high molecular weight in the transforming principle. They had extracted DNA. This was the agent capable of causing a long-lasting, heritable change in an organism.
Thus, it can be written as DNA of heat-killed ‘S’ + R type + DNAase —> a virulent strain
The correct option is A

Note: Since the DNA was broken down by the enzyme, only R cells develop when a DNAse is added, the genetic information must be in the DNA. Even though transformation occurred in some bacteria, it was incapable of being replicated in other bacteria (or higher organisms), as its significance appeared to be limited to medicine.