Question

How did Avery, McLeod and McCarty prove that DNA was the genetic material. Explain.

Answer 1

Oswald Avery, Colin MacLeod, and Maclyn McCarty showed that DNA (not proteins) can transform the properties of cells, clarifying the chemical nature of genes, while studying Streptococcus pneumoniae, bacteria that can cause pneumonia. Avery and members of his lab studied transformation in fits and starts over the next 15 years. In the early 1940s, they began a concerted effort to purify the "transforming principle" and understand its chemical nature.

Avery and McCarty observed that proteases - enzymes that degrade proteins - did not destroy the transforming principle. Neither did lipases - enzymes that digest lipids. They found that the transforming substance was rich in nucleic acids, but Ribonuclease, which digests RNA, did not inactivate the substance. They also found that the transforming principle had a high molecular weight. They had isolated DNA. This was the agent that could produce an enduring, heritable change in an organism.