A students was repeating the experiments of Alfred Hershey and Maltha Chase (1952). Results obtained by him are shown in the given figure. Select the biomolecule that was radio actively labelled by the students for his experiment.

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CUET Biology 23rd Aug 2022 Official Paper

Answer 1

Concept:

Alfred Hershey and Martha Chase performed an experiment in 1952 that proved that DNA is the genetic material.
Experimental model - Bacteriophages, which are viruses that attach to bacteria and transfer their genetic material into the bacterial cell.
The experiment was based on the knowledge that:
- DNA - contains Phosphorus (P), but no Sulfur (S).
- Protein - contains sulfur (S), but no Phosphorus (P).

Important Points

Steps of Experiment -
1. Infection - E. coli cells were infected with the radioactive bacteriophages, so that the genetic material could be transferred to the bacteria.
2. Blending - The virus coats were separated from the bacteria by agitating them with the help of a blender.
3. Centrifugation - They were then centrifuged to separate the bacterial cells and viral coats as precipitate and supernatant respectively.
Given Observation -
- Radioactivity was found in the precipitated pellets, which represent the bacterial cell.
Conclusion -
- Radioactivity in bacterial cells indicates that the radioactive DNA is present in the cells.
- Therefore, we can say that the DNA of bacteriophage was radio-labelled with Phosphorous.

Hence, the correct answer is option 1.