Brent Cornell

    
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

• Viruses (T2 bacteriophage) were grown in one of two isotopic mediums in order to radioactively label a specific viral component
  • Viruses grown in radioactive sulfur (³⁵S) had radiolabelled proteins (sulfur is present in proteins but not DNA)
  • Viruses grown in radioactive phosphorus (³²P) had radiolabeled 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 larger bacteria formed a solid pellet while the smaller viruses remained in the supernatant

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

Summary of the Hershey-Chase Experiment