What was the key contribution of Avery, MacLeod, and McCarty to DNA history?

What was the key contribution of Avery, MacLeod, and McCarty to DNA history?

• A. Proteins Are The Transforming Principle, Demonstrated by Purified Protein From S Cells
• B. DNA Is the Transforming Principle, Demonstrated by Purified DNA From S Cells
• C. RNA Is The Transforming Principle, Demonstrated by Purified RNA From S Cells
• D. Lipids Are The Transforming Principle, Demonstrated by Purified Lipids From S Cells

Answer: (B)

The main concept being tested is which molecule can carry genetic information and induce a transformable change in cells. Avery, MacLeod, and McCarty showed that DNA is the substance responsible for transformation. They started from Griffith’s observation that dead virulent S bacteria could convert live avirulent R bacteria into virulent forms. By using purified material from S cells and selectively destroying different types of molecules with specific enzymes, they found that removing DNA stopped the transformation, while destroying proteins or RNA did not. They also demonstrated that adding purified DNA from S cells to R cells could produce transformation. This provided strong, direct evidence that DNA alone carries the genetic information, not proteins, RNA, or lipids. This work redirected the field toward DNA as the carrier of heredity in bacteria and laid the groundwork for the growth of molecular genetics.

The main concept being tested is which molecule can carry genetic information and induce a transformable change in cells. Avery, MacLeod, and McCarty showed that DNA is the substance responsible for transformation. They started from Griffith’s observation that dead virulent S bacteria could convert live avirulent R bacteria into virulent forms. By using purified material from S cells and selectively destroying different types of molecules with specific enzymes, they found that removing DNA stopped the transformation, while destroying proteins or RNA did not. They also demonstrated that adding purified DNA from S cells to R cells could produce transformation. This provided strong, direct evidence that DNA alone carries the genetic information, not proteins, RNA, or lipids. This work redirected the field toward DNA as the carrier of heredity in bacteria and laid the groundwork for the growth of molecular genetics.