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InterviewSolution
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Question : Hershey and Chase experiment with bacteriophage showed that |
| Answer» Solution :Alftred Hershey and Martha Chase (1952) conducted experiments on bacteriophages that infect bacteria. PHAGE `T_(2)`, is a virus that infects the bacterium Escherichia coli. When PHAGES (Virus) are added to bacteria, they adsorb to the outer surface, sóme material enters the bacterium, and then later each bacterium lyses to release a large number of progeny phage. Hershey and Chase wanted to observe whether it was DNA or protein that entered the bacteria. All nucleic acids contain phosphorus, and contain sulphur (in the amino acid cysteine and methionine). Hershey and Chase designed an experiment using radioactive isotopes of Sulphur `""^(35)S`and phosphorus `""^(32)P` to keep SEPARATE track of the viral protein and nucleic acids during the infection process. The phages were allowed to infect bacteria in culture medium which containing the radioactive isotopes `""^(35)S` or `""^(32)P`. The bacteriophage that grew in the presence of `""^(35)S` had labelled proteins and bacteriophages grown in the presence of P had labelled DNA. The differential labelling thus enabled them to identify DNA and proteins of the phage. Hershey and Chase mixed the labelled phages with unlabeled E. coli and allowed bacteriophages to attack and inject their genetic material. Soon after infection before lysis of bacteria), the bacterial cells were gently agitated in a blender to loosen the adhering PHASE particles. It was observed that only `""^(32)P` was found associated with bacterial cells and `""^(35)S` was in the surrounding medium and not in the bacterial cells. When phage progeny was studied for radioactivity, it was found that it carried only `""^(32)P` and not `""^(35)S`. These results clearly indicate that only DNA and not protein coat entered the bacterial cells. Hershey and Chase thus conclusively proved that it was DNA, not protein, which carries thehereditary information from virus to bacteria. | |