how did hershey and chase proved that DNA is the genetic material in 3 marks
Answers
Answer:
The unequivocal proof that DNA is the genetic material was given by Hershey and Chase.
They grew viruses in two different medium containing radioactive phosphorous and radioactive sulfur. The viruses which were grown in radioactive P had radioactive DNA but not radioactive protein. The reverse happened to the ones that grew in radioactive S.
Now these viruses were allowed to infect to E. coli bacteria. The genetic material of virus blends with the genetic material of bacteria and transforms it.
It was found that the bacteria which was infected with viruses having radioactive DNA were radioactive and the same did not happen to the ones with radioactive protein.
Henceforth it was proved that DNA is the genetic material.
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Answer:
(1) Hershey and Chase worked with bacteriophages (viruses that infect bacteria and which are composed of DNA and protein coat).
(2) They cultured E. coli bacteria in medium containing radioactive phosphorus 32_p. By infecting these bacteria with bacteriophages, Hershey and Chase could develop bacteriophages having DNA labelled with 32_p. as DNA contains phosphorus and proteins do not.
(3) They also cultured E. coli bacteria in medium containing radioactive sulphur 35s By infecting these bacteria with bacteriophages, they developed bacteriophages whose protein coat was labelled with 35s as proteins contain Sulphur and DNA does not.
[Note: Viruses cannot be cultivated in medium.]
(4) Experiment involved three steps.
(a) Infection: Both the types of radioactive phages were allowed to infect E.colt bacteria grown on the medium containing normal "P and 's.
(b) Blending: Then bacterial cultures were agttated in blender to break contact between bacterial and parts of viruses that did not enter bacterial cells.
(c) Centrifugation: lt was done to separate bacterial cells as a pellet. Parts of viruses which did not enter bacteria remained in the suspension.
(5) Observation:
(a) Radioactives remained in suspension.
(b) Only radioactive P was found inside the bacterial cell in the pellet.
(c) Thus it was proved that DNA is the genetic material which enters bacterial cell and not protein.