HERSHEY AND CHASE EXPERIMENT

• ‘DNA is the genetic material’ is demonstrated  by Alfred Hershey and Martha Chase (1952).. This experiment known as the blender experiment because a kitchen waring blender was used as a major piece of apparatus They demonstrated that the DNA injected by a phage particle into a bacterium contains all the information required to synthesize progeny phage particles.
  • A single particle of phage T2 consists of DNA encased in a protein shell . The DNA is the only phosphorus containing substance in the phage particle; the proteins of the shell, which contain the amino acids methionine and cysteine, have the only sulphurm atoms.
  •  In these experiments, phage DNA was made radio-active by growing infected bacteria on a medium containing radioactive phosphate(32PO4). Since phage proteins do not contain phosphorus, only DNA would be labelled.
    Similarly, phage proteins were labelled with the help of 35SO4. Since DNA does not contain sulphur, only protein would be labelled with 35S. 
  • Such differential labelling would enable one to distinguish between DNA and proteins of the phage without performing any chemical tests. 
  • Hershey and Chase then allowed both kinds of labelled phage particles to infect E. coli bacteria . The infected bacteria were immediately agitated in a waring blender. After shaking, only radioactive32P was found associated withbacterial cells and 35S was found only in surrounding medium and not in bacterial cells. When phage progeny was studied for radioactivity in this experiment, it was found that the phage progeny
    carried labelled only with 32P. 
  • The progeny was not labelled with 35S. This clearly indicates that only DNA and not protein is
  • injected into bacterial cells. The empty protein coat (ghost) left outside.
  • Thus, Hershey and Chase experiment proved that DNA entering the host cell carries all the genetic information or synthesis of new phage particles, hence, is the sole genetic material in DNA bacteriophages (e.g., T2).

 
Reference: Life: The Science of Biology, 7th Edition  David E. Sadava, David M. Hillis, H. Craig Heller,