Question

(a)Write the conclusion drawn by Griffith at the end of his experiment with Streptococcus pneumoniae.
(b) How did Avery, C. MacLeod and M.McCarty prove that DNA was the genetic material? Explain.

Answer 1

Answer:

(a) Frederick Griffith (1928) performed the experiments on Bacterial transformation with Streptococcus pneumoniae, the bacterium that causes pneumonia. He concluded that the R-strain had somehow been transformed by the heat-killed S-strain bacteria. Some transforming principle, transferred from the heat killed S strain had enabled the R strain to synthesize a smooth polysaccharide coat and become virulent and this must be due to the transfer of genetic material.

(b) Avery, MacLeod and McCarty’s experiment

* They purified biochemicals like proteins, DNA and RNA from the heat-killed S- cells.

* When these fractions were added individually to the culture of live R-cells, only DNA was able to cause transformation of R-cells into S-cells.

* They also found that protein digesting enzymes and RNA- digesting enzymes did not affect transformation indicating that transforming substance is not a protein or RNA.

* Digestion with DNase did inhibit transformation. This suggests that DNA caused transformation and therefore DNA is the genetic material.

Answer 2

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Oswald Avery, Colin MacLeod, and Maclyn McCarty showed that DNA (not proteins) can transform the properties of cells, clarifying the chemical nature of genes. Avery, MacLeod and McCarty identified DNA as the "transforming principle" while studying Streptococcus pneumoniae, bacteria that can cause pneumonia.......