The sequence of the steps of the experiment conducted by Hershey and Chase were:
(A) Viral particles were separated by centrifugation.
(B) Some viruses were grown on radioactive sulphur whereas others were grown on radioactive phosphorus
(C) Radioactive phages were allowed to attach E.coli
(D) Viral coats were removed from the bacteria
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (B), (C), (D), (A)
(B) Some viruses were grown on radioactive sulphur whereas others were grown on radioactive phosphorus — this comes first. Radioactive phosphorus marks the DNA of the virus, and radioactive sulphur marks its protein.
(C) Radioactive phages were allowed to attach E.coli — this comes second. The labelled phages infect the bacteria.
(D) Viral coats were removed from the bacteria — this comes third. The coats are shaken off by agitating the bacteria in a blender.
(A) Viral particles were separated by centrifugation — this comes last. The virus particles are spun away from the bacteria in a centrifuge. The bacteria infected with phages that had radioactive DNA were radioactive. This showed that DNA is the genetic material.
NCERT Extract:
The Genetic Material Is DNA – “… Hershey and Chase worked to discover whether it was protein or DNA from the viruses that entered the bacteria. They grew some viruses on a medium that contained radioactive phosphorus and some others on medium that contained radioactive sulfur. Viruses grown in the presence of radioactive phosphorus contained radioactive DNA but not radioactive protein because DNA contains phosphorus but protein does not. Similarly, viruses grown on radioactive sulfur contained radioactive protein but not radioactive DNA because DNA does not contain sulfur. Radioactive phages were allowed to attach to E. coli bacteria. Then, as the infection proceeded, the viral coats were removed from the bacteria by agitating them in a blender. The virus particles were separated from the bacteria by spinning them in a centrifuge.”