How did the 3 scientist prove that DNA is a genetic material

Griffiths experiment only suggested a transforming substance but it was not proved by this work that DNA is the genetic material.

• Avery, McLeod, and McCarthy worked to determine the biochemical nature of genetic material responsible for transformation.
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• This suggests that DNA has to be the genetic material.

Hershey and Chase Experiment to Confirm DNA as the Genetic Material

• Hershey and Chase chose to work on bacteriophages i.e. the viruses that infect bacteria.
• When a bacteriophage infects a bacterium, the genetic material of the virus gets attached to the genetic material of bacteria and bacteria then treats the viral genetic material as its own to synthesise more viral particles.
• Hershey and Chase wanted to discover whether the part that entered the bacteria from the virus was a protein or DNA.
• They labelled some phages with radioactive sulphur and the others with radioactive phosphorus.
• These radioactive phages were used to infect E. coli.
• E.coli was then blended and centrifuged to remove viral particles.
• It was observed that bacteria with radioactive DNA were radioactive while those with radioactive proteins lost their radioactivity.
• This showed that it is the DNA that enters the bacteria from viruses and not proteins. Hence, it was concluded that DNA is the genetic material. 
                     

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