Final answer:
The Avery, MacLeod, and McCarty experiment aimed to discover the chemical identity of the transforming principle noted by Griffith. They found that only when DNA was degraded could the R cells no longer be transformed, indicating that DNA is the material responsible for heredity.
Step-by-step explanation:
The simpler design of Avery, MacLeod, and McCarty was a follow-up experiment to Griffith's work, aiming to pin down the chemical identity of the transforming principle. They performed a systematic elimination study wherein they isolated the components (DNA, proteins, carbohydrates, lipids) of heat-killed S-cells.
Each component was tested for its ability to transform R cells in vitro. They used specific enzymes to degrade each molecular component and observed the transformation effects on R cells. They found that when DNA was destroyed, the R cells could no longer be transformed, suggesting that DNA was the critical factor in transmitting genetic information.
If proteases (which degrade proteins) had prevented transformation in their experiments, the conclusion would have been that proteins were the carriers of genetic information. However, this was not the case; only when DNA was degraded was the ability to transform R cells lost.
Their results thus suggested that DNA, not protein or any other molecule, was the substance responsible for genetic transformation, supporting the idea that DNA is the material of heredity.