Hershey and Chase conducted experiments on
bacteriophage to prove that DNA is the genetic material.
(i) Some bacteriophage virus
were grown on a medium that contained radioactive phosphorus (32P)
and some in another medium with radioactive sulphur (35S).
(ii) Viruses grown in the
presence of radioactive phosphorus (32P) contained radioactive DNA.
(iii) Similar viruses grown in
presence of radioactive sulphur (35S) contained radioactive protein.
(iv) Both the radioactive virus
types were allowed to infect E. coil separately.
(v) Soon after infection, the
bacterial cells were gently agitated in blender to remove viralcoats from the
(vi) The culture was also
centrifuged to separate the viral particle from the bacterial cell.
Observations and Conclusions
(i) Only radioactive32Pwas
found to be associated with the bacterial cell, whereasradioactive35S
was only found in surrounding medium and not in the bacterial cell.
(ii) This indicates that only
DNA and not protein coat entered the bacterial cell.
(iii) This proves that DNA is
the genetic material which is passed from virus to bacteria and not protein.
If both DNA and proteins
contained phosphorus and sulphur, the result might change.
In case (i)
Radioactive35S and +
Bacteriophage32Plabeled protein capsule No radioactive
in cells + Radioactivity (35Sand 32P) detected in
In case (ii)
Radioactive35S and 32Plabeled
DNA ? Bacteriophage Radioactive32P
and35S Detected in cells - No radioactivity detected in supernatant.
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