Question

explain how the Hershey-Chase experiment conclusively proved that DNA and not protein was the genetic material?

Answer 1

Hershey and Chase used radioisotopes of sulfur and phosphorous to keep separate track of viral proteins and nucleic acids during the infection process of E.coli by T4 bacteriophage. The phages were labelled by having them infect bacteria grown in culture containing the radioisotopes ³⁵S or ³²P. When ³²P-labelled phages were mixed with unlabelled E.coli cells, they found that the ³²P label entered the bacterial cells and the next generation of the phages that burst from the infected cells carried ³²P label. When ³⁵S-labelled phages were mixed with unlabelled E.coli, they found that the ³⁵S label stayed outside the bacteria for the most part.Hershey and Chase thus demonstrated that the outer protein coat of a phage does not enter the bacterium it infects, wheras the phage's inner material, consisting of DNA , does enter the bacterial cell. Since the DNA is responsible for the production of the new phages during the infection process, the DNA, not the protein , must be the genetic material. In this way Hershey and Chase concluded that DNA is the genetic material.