Question

Describe the experiment of Hershey and Chase to prove that DNA is the genetic material.

Answer 1

(1) Hershey and Chase performed their experiments with bacterium E. coli and bacteriophage $T_2$.
(2) The bacteriophage which has a DNA and a protein coat attaches to the bacteria and transfers its genetic material into the bacterial cell.
(3) Some $T_2$ phages were grown in medium with radioactive, sulphur (${}^{35}S$) and the other $T_2$ phages were grown in a medium with radioactive phosphorous (${}^{32}P$).
(4) The $T_2$ in (${}^{35}S$) medium contained radioactive protein because the DNA does not contain sulphur whereas the $T_2$ phages in (${}^{32}P$) medium contained radioactive DNA because the protein coat does not contain phosphorus.
(5) The radioactive phages then attached to the E.coli. After the infection progressed, the viruses were separated by centrifugation.
(6) The E.coli infected by $T_2$ phage which had radioactive DNA were also radioactive, indicating that DNA was the material that passed from the virus to the bacteria.
(7) The bacteria that had been infected by the virus with a radioactive protein coat was not radioactive i.e., the protein had not entered the bacteria thus proving that DNA was the genetic material that is passed from a virus to a bacteria.