Question

1. Why did Hershey and Chase use ‘³⁵S’ and ‘³²P’ in their experiment? Explain.    [1]
2. State the importance of
   1. blending and    [1]
   2. centrifugation in their experiment.    [1]
3. Write the conclusion they arrived at the end of their experiment.    [2]

Answer 1

1. Hershey and Chase experimented with radioactive isotopes of phosphorus-32 (³²P) and sulfur-35 (³⁵S) to differentiate between DNA and protein in bacteriophages.
   Hershey and Chase experimented with radioactive isotopes of phosphorus-32 (³²P) and sulfur-35 (³⁵S) to differentiate between DNA and protein in bacteriophages.
   As DNA contains phosphorus but no sulphur, it is referred to as phosphorus-32 (³²P). In order to monitor the position of DNA during viral infection, Hershey and Chase included ³²P into the bacteriophage's DNA component.
   Hershey and Chase were able to ascertain that the bacteriophage's DNA, not its protein, enters the bacterial cell during infection by using these radioactive isotopes.
2. Blending: Blending enabled the physical separation of bacteriophage protein coats from bacterial cells post-viral infection.
   Centrifugation: Centrifugation enabled the separation of bacteriophage protein coats from bacterial cells and their contents. Upon centrifuging the bacteriophage-infected bacterial suspension, the denser bacterial cells and their constituents, including any virus DNA or RNA, were sedimented at the bottom of the tube, while the lighter protein coatings remained in the supernatant.
3. Hershey and Chase's experiment revealed that DNA, not protein, is responsible for heredity and inheritance.