Present an overview of two classical experiments that
demonstrated that dna is the genetic material. can rna be the
genetic material? explain.

Explanation:

A) Fredrick Griffith Bacterial Transformation Experiment

In 1928 Fredrick worked on various strains on Staphylococcus pneumoniae

and mice.

He was trying to develop a vaccine against pneumonia.

He chose two strains of bacteria,

R stain- rough and non virulent strain

S strain- smooth and virulent strain

when he injected the strains one by one into the mice these were the results-

R strain into the mice  > Mice lives

S strain into the mice  > Mice gets pneumonia and dies

Heat killed S strain     > Mice lives

R starin + Heat killed S strain> Mice dies

Thus, Griffith concluded that The living R strain must have taken a 'transforming principle' from the heat killed S train and became virulent. This resulted in the death of the mice.

B) Hershey Chase experiment

They used bacteriophages to conduct this experiment. Their phase was made up of protein and contained DNA.

To determine that whether the phage added proteins or DNA to the host cell in order to multiply, he radiolabeled the components of the phage

Proteins were labelled by 35S

DNA was labelled with  32P

He infected various batches of bacterial culture with these radiolabelled bacteriophage.

Then he centrifuged the culture and got a pellet( heavy material like bacteria) and supernatant( light material like media, phages).

He found that pellet was mostly labelled with 32P and not 35S. Hence they concluded that it DNA and not protein were the genetic material.

RNA stores the genetic material. In fact RNA was the first genetic molecule and it was only after evolution that DNA became the genetic molecule.

-RNA has a great capacity of storing and expressing the genetic information.

-But the single stranded structure of RNA is unstable and can be easily destroyed by the enzymes.

-Hence the double stranded nature of DNA is much more stable and and passes the genetic information with more accuracy.