Question

How did hershey and chase proved that dna is the genetic material?

Answer 1

Answer:

Hershey and Chase worked with bacteriophage and E.coli to prove that DNA is the genetic material. They used different radioactive isotopes to label DNA and protein coat of the bacteriophage. They grew some bacteriophages on a medium containing radioactive phosphorus (32P) to identify DNA and some on a medium containing radioactive sulphur (35S) to identify protein. Then, these radioactive labelled phages were allowed to infect E.coli

bacteria. After infecting, the protein coat of the bacteriophage was separated from the bacterial cell by blending and then subjected to the process of centrifugation. Since the protein coat was lighter, it was found in the supernatant while the infected bacteria got settled at the bottom of the centrifuge tube. Hence, it was proved that DNA is the genetic material as it was transferred from virus to bacteria.

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Answer 2

Answer:

Hershey and Chase performed experiment in three steps:

1. Infection
2. Blending
3. Centrifugation

• Hershey and Chase raised $\sf T_{2}$ bacteriophage over two different bacterial colonies. One having radioactive  phosphorus $\sf P^{32}$ and the other having radioactive sulphur $\sf S^{35}$.
• Radioactive sulphur got incorporated in the capsid  proteins of bacteriophage.
• Radioactive phosphorus $\sf P^{32}$ became component of DNA of bacteriophage.
• The two  types of bacteriophages were introduced to infect different bacterial colonies of E. coli. The two cultures were  taken out and independently agitated on a blender. The empty phage capsid got separated from the bacterial  cells. The virus particles were separated from the bacteria by spinning them in a centrifuge.

• Bacteria which was infected with viruses that had radioactive DNA were radioactive, indicating the DNA was  the material that passed from virus to the bacteria.
• Bacteria that were infected with viruses that had radioactive  proteins were not radioactive. This indicates that protein did not enter the bacteria from the viruses.

DNA is  therefore the genetic material.