Question

How did Hershey and Chase differentiate between DNA and protein in their experiment while proving that DNA is the genetic material?

Answer 1

Hershey and Chase, in order to prove DNA as genetic material, cultured E. coli bacteria in medium containing P³² and P³² isotopes. After growing for some time, the bacteria were infected by bacteriophage. After infection, it was observed that the protein coat of bacteriophage had become radioactive with S³⁵ whereas its DNA does not contain sulphur. On the contrary, the DNA of the bacteriophage was showing the presence of P³² radioactive isotopes because DNA contains phosphorus. P³² was absent in the protein coat. Bacteriophage containing P³² radioactive elements was infected with such bacteria which did not contain radioactive elements. After infection, it was observed that all the bacteria had become radioactive. Most of the radioactive isotopes were also transferred to the next generation of bacteriophage.

On infecting bacteria devoid of radioactive elements with bacteriophage containing S³² and then separating the bacteriophage, it was observed that radioactive elements were not present in the bacteria but these remained in the protein envelope of the bacteriophage. The above experiment proves that the DNA of the bacteriophage is the substance which produces new bacteriophages and takes part in infection. It has been proved that DNA is the genetic material and not protein. Besides this, DNA contains phosphorus whereas protein does not contain phosphorus. DNA is devoid of sulphur whereas protein contains sulphur.