Alfred Hershey and Maratha chase - Ultimately proven DNA is genetic material

• The ultimate proof that DNA is genetic material  came from the experiments of Alfred  Hershey and Maratha chase.

• In  I952, Hershey-Chase conducted an experiment to prove that DNA is genetic material but not the protein.

• They  experimented by using the Bacteriophages. Bacteriophages are the viruses that can  infect and replicate within bacteria.

• They grew the Bacteriophages  in two different mediums.

• Some bacteriophages were grown in a medium  containing radioactive phosphorus ( 32P). Bacteriophages that was cultured or grew in this medium, had DNA with radioactive phosphorus ( 32P) because phosphorus is present as an important constituent in DNA.

• On the other hand, Some bacteriophages were grown in a medium containing  radioactive sulphur (35S). 

• Bacteriophages that were cultured or grew in this medium, had a protein coat  with radioactive phosphorus ( 32P) because sulphur is present as an important constituent in protein.

CASE - FIRST 

• When Bacteriophage with radioactive sulphur (35S) was allowed to infect the  Bacteria E.Coli.

• After the infection, When viral protein coat was separated from bacteria through an agitator system, it was found that radioactive sulphur ( 35S) was not present in the body of E. Coli.

• A  protein coat containing radioactive sulphur was present outside the body of E.Coli because the virus renders its protein coat  outside during infection. 

CASE - SECOND 

• When Bacteriophage with radioactive phosphorus (32P) was allowed to infect the  Bacteria E.Coli.

• After the infection, When virus was separated from bacteria through an agitator system, it was found that radioactive sulphur ( 35S) was  present in the body of E. Coli.

• During infection, the genetic matter was transferred from bacteriophage to the body of E.Coli.

CONCLUSION

• Hershey and Chase found that in both cases when bacteriophage were separated from E.Coli through the centrifugation.

• They observed a protein coat containing 35S was not transferred from bacteriophage to E.Coli therefore radioactive 35S was not detected in the body of E.Coli.

• In another case, the genetic matter with 32P of Bacteriophage was transferred to the body of E.coli and 32P was detected in the body of E.coli.

• Hence both stated that DNA has capability for transferring from one cell to another cell but protein is not able to do so. Hence DNA is genetic matter. DNA was thus proved to be the genetic material.