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Question
Why did Hershey and Chase use radioactively labelled phosphorous and sulphur only? Would they have got the same result if they use radiolabelled carbon and nitrogen?
Solution
Generally proteins contain sulphur but not phosphorous and nucleic acid (DNA) contains, phosphorous but not sulphur. Hence Hershey - Chase used radioactive isotopes of sulphur (35S) and phosphorus (32P) to keep separate track of viral protein and nucleic acid in culture medium. The expected result cannot be achieved, if radioactive carbon and nitrogen is used, since these molecules are present in both DNA and proteins.
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