DNA is the Genetic Material:
Harshey and Chase Experiment:
· The proof for DNA as the genetic material came from the experiments of Alfred Hershey and Martha Chase (1952), who worked with bacteriophages.
· The bacteriophage on infection injects only the DNA into the bacterial cell and not the protein coat; the bacterial cell treats the viral DNA as its own and subsequently manufactures more virus particles.
· They made two different preparations of the phage; in one, the DNA was made radioactive with 32p and in the other, the protein coat was made radioactive with 35S.
· These two phage preparations were gently agitated in a blender to separate the adhering protein coat of the virus from the bacterial cells.
· The culture was also centrifuged to separate the viral coat and the bacterial cells.
· It was found that when the phage containing radioactive DNA was used to infect the bacteria, its radioactivity was found in the bacterial cells (in the sediment) indicating that the DNA has been injected into the bacterial cell.
· So, DNA is the genetic material and not proteins.
The Hershey-Chase experiment