Hershey and Chase Experiment; DNA is the genetic material

In the mid-twentieth century, scientists were still unsure as to whether DNA or protein was the genetic material of the cell. It was known that some viruses consisted solely of DNA and a protein coat and could transfer their genetic material into hosts. In 1952, Alfred Hershey and Martha Chase conducted a series of experiments to prove that DNA was the genetic material. The protein of bacteriophage was radioactively labeled with sulfur (35S) (sulfur is present in proteins but not DNA) and the DNA was radioactively labeled with radioactive phosphorus (32P) DNA (phosphorus is present in DNA but not proteins). The viruses were then allowed to infect a bacterium (E. coli) and then the virus and bacteria were separated via centrifugation. The bacterial pellet was found to be radioactive when infected by the 32P–viruses (DNA) but not the 35S–viruses (protein). This demonstrated that DNA, not protein, was the genetic material because DNA was transferred to the bacteria

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