Question

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

Answer 1

The most well-known Hershey-Chase experiment was the last experiment, also called the Waring Blender experiment, in which Hershey and Chase discovered that phages only inserted their DNA into host bacteria, and that the DNA served as the genetic element replicating the phages.

Complete answer:
(1) Experiments conducted with Bacterium E by Hershey and Chase. Bacteriophage T2 and coli.
(2) The bacteria bind to the DNA and protein-coated bacteriophage and transfer their genetic material to the bacterial cell.
(3) Some T2 phages were grown with sulfur in a radioactive medium (35S) and the other T2 phages were grown with sulfur in a radioactive phosphorous medium (35S) (32P).
(4) In the (35S) medium, the T2 phages contained radioactive protein because the DNA did not contain sulfur, while in the (32P) medium, the T2 phages contained radioactive DNA because the protein coat did not contain phosphorus.
(5) E.coli is then bound to the toxic phages. The viruses were segregated by centrifugation after the infection progressed.
(6) Also radioactive were E.coli contaminated with T2 phage that had radioactive DNA, suggesting that DNA was the substance that transferred from the virus to the bacteria.
(7) The bacteria infected with a nuclear protein coat by the virus were not radioactive, i.e. the protein had not reached the bacteria, thereby indicating that the genetic material transmitted from the virus to the bacteria was DNA.

Note: In the Hershey-Chase experiment, 32P (phosphorus) was used because phosphorus is found in deoxyribonucleic acid (DNA), but not in proteins. Therefore, to mark only the proteins, 35S was used because DNA does not contain sulfur.