Arrange the following steps of Hershey-Chase experiment regarding “DNA as genetic material” in correct sequence.
A. Blending
B. Centrifugation
C. Radioactive labelling
D. Infection
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → C, D, A, B
C. Radioactive labelling — first. Hershey and Chase grew some bacteriophages (viruses that infect bacteria) on a medium with radioactive phosphorus, which labels DNA. They grew others on a medium with radioactive sulfur, which labels protein.
D. Infection — second. The radioactive phages were allowed to attach to E. coli bacteria. The genetic material of the virus entered the bacteria.
A. Blending — third. As the infection went on, the bacteria were shaken in a blender. This removed the empty viral coats from the outside of the bacteria.
B. Centrifugation — last. Spinning in a centrifuge separated the virus particles from the heavier bacteria. Bacteria infected with phages carrying radioactive DNA were radioactive. Those infected with phages carrying radioactive protein were not. So DNA, not protein, 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.”