Final answer:
Avery, MacLeod, and McCarty's experiments tested the transforming ability of purified components from the S strain of pneumococcus on R cells, concluding that DNA is the molecule of heredity when only the degradation of DNA stopped the transformation process.
Step-by-step explanation:
The hypothesis of the Avery, MacLeod, and McCarty experiments was that a distinct substance from heat-killed virulent bacteria was responsible for transforming non-virulent bacteria into virulent strains, a phenomenon observed by Griffith known as transformation. The experiment involved isolating and purifying various components such as DNA, proteins, carbohydrates, and lipids from the heat-killed S strain of pneumococcus and determining which one caused the non-virulent R strain to become virulent when added in a test tube environment, effectively transforming them.
To identify the transforming principle, they treated the isolated components with specific enzymes that would degrade each type of molecule. Their findings revealed that only the degradation of DNA with DNase stopped the transformation from occurring. The R cells remained non-virulent when DNA was destroyed, pointing to DNA as the material responsible for transformation. Their conclusions were pivotal, providing strong evidence that DNA was the molecule of heredity, despite the initial skepticism in the scientific community due to DNA's apparent simplicity compared to proteins.