Hershey & Chase Experiment

Many scientists worked and gave their results in search of DNA is a genetic material. The final proof for DNA as the genetic material came from the experiment of Alfred Hershey and Martha Chase (1952), who worked with bacteriophage.

Bacteriophage are the viruses that infect bacteria and they have a protein coat and DNA.

Experiment:

• They made two different preparations of the phase. In one the DNA was made radioactive with P³² and in the other protein coat was made radioactive with S³⁵ .
• 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.
• Bacteria which were infected with viruses that had radioactive DNA were radioactive and indicating that DNA was the material that passes from virus to bacteria.
• Bacteria that were infected with viruses that had reactive protein coat were not radioactive.

DNA is, therefore, the genetic material that pass from virus to bacteria.

Q. Why was the Hershey-Chase experiment important?

Ans. It confirmed the result of Avery who proved that  DNA transferred from one bacterium to other bacteria. Bacteriophage injects its radioactive DNA into the bacteria ( not protein) which proved that DNA is a hereditary material.

Q. Why do Harshey And Chase use radioactive phosphorus and radioactive sulphur?

Ans. They used radioactive phosphorus for DNA because DNA contains phosphorus but proteins do not contain phosphorus.

Same as they used sulphur for protein coat because protein contains sulphur but DNA do not contain sulphur.

Characteristics of Genetic Material:

A molecule that can act as genetic material must have following properties:

Replication:

It should be able to generate its replica.

Stability:

It should be chemically and structurally stable.

Mutation:

It should be provided the scope for slow changes that are necessary for evolution.

Genetic expression:

It should be able to express itself in the form of mendelian characters