Choose the correct statements about the work of Oswald Avery, Colin MacLeod and Maclyn McCarty from the following:
A. Avery, MacLeod and McCarty purified biochemicals such as proteins, DNA and RNA from the heat-killed S cells.
B. Avery, MacLeod and McCarty found that RNA-digesting enzymes (RNases) inhibited transformation.
C. Avery, MacLeod and McCarty found that digestion with DNase inhibited transformation.
D. Before the work of Avery, MacLeod and McCarty, the genetic material was thought to be a protein.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, C and D only
Griffith showed that a ‘transforming principle’ from heat-killed S bacteria could change live R bacteria into the virulent S form. Avery, MacLeod and McCarty set out to find what this principle was made of. They used enzymes that destroy one kind of molecule each, and checked whether transformation still took place.
A. Avery, MacLeod and McCarty purified biochemicals such as proteins, DNA and RNA from the heat-killed S cells. — True. They separated these molecules from the heat-killed S cells to test which one could transform live R cells into S cells.
B. Avery, MacLeod and McCarty found that RNA-digesting enzymes (RNases) inhibited transformation. — False. RNases did not affect transformation, and neither did proteases. So the transforming substance was neither RNA nor protein.
C. Avery, MacLeod and McCarty found that digestion with DNase inhibited transformation. — True. DNase destroys DNA. When the DNA was destroyed, transformation stopped, which showed that DNA caused it.
D. Before the work of Avery, MacLeod and McCarty, the genetic material was thought to be a protein. — True. Proteins were the favoured choice before their work (1933-44). Their result pointed to DNA instead.
NCERT Extract:
Biochemical Characterisation of Transforming Principle – “Prior to the work of Oswald Avery, Colin MacLeod and Maclyn McCarty (1933-44), the genetic material was thought to be a protein. They worked to determine the biochemical nature of ‘transforming principle’ in Griffith’s experiment.
They purified biochemicals (proteins, DNA, RNA, etc.) from the heat-killed S cells to see which ones could transform live R cells into S cells. They discovered that DNA alone from S bacteria caused R bacteria to become transformed.
They also discovered that protein-digesting enzymes (proteases) and RNA-digesting enzymes (RNases) did not affect transformation, so the transforming substance was not a protein or RNA. Digestion with DNase did inhibit transformation, suggesting that the DNA caused the transformation.”