Question

Discuss how DNA was discovered to be the genetic material

Answer 1

Based on the transforming principles of Griffith experiment, in 1944 Oswald Avery, colin Macleod and Maclyn McCarty given the solid evidence of DNA as the gentic material.

Following are the key observations of Oswald Avery, colin Macleod and Maclyn McCartys eveidence:

1. It was observed that the transformation carried out in heat killed S strain bacteria was inhibited when the highly purified extract of starin was subjected to activity of pancreatic Deoxyribonucleases.

2. During the evidence it was also found that the proteases enzymes which are protein digesting and RNAses which RNA digesting enzymes did not affect the transformation.

Hence bases on thsese observation they concluded that DNA is the genetic material and caused the transformation from heat-killed virulent bacteria to the live non-virulent bacteria.

The second proof: In 1952, Alfred Hershey and Martha Chase experiment:

They worked with the virus bacteriophage T2 which infects the E. coli. This phase is proetin coated DNA.

They labelled T2 phase which conatin the nucleic acid with radioisotope phosphurus and protein coat with radioactive sulphur. They infected with E. coli with labelled T2 phase and after infection it was observed that radioactive phosporus remained in the cells and radioactive sulphur lost. This indicate that proteins did not enter in to E. coli from bacteriophage T2.

Therefore it was concluded that DNA was the genetic material which passed from T2 phase.