Explain why Avery, MacLeod, and McCarty's in vitro transformation experiment showed that DNA, but not RNA or protein, is the hereditary molecule.

Key Concepts

DNA as the Genetic Material

Avery, MacLeod, and McCarty's experiment demonstrated that DNA is the molecule responsible for heredity. They showed that when DNA from a virulent strain of bacteria was introduced to a non-virulent strain, the latter transformed into a virulent form, indicating that DNA carries the genetic instructions necessary for this transformation.

In Vitro Transformation

In vitro transformation refers to the process of introducing foreign DNA into a cell in a controlled environment outside of a living organism. In their experiment, the researchers isolated DNA from pathogenic bacteria and mixed it with non-pathogenic bacteria, observing that only the DNA could induce a change, thus supporting the idea that DNA is the hereditary material.

Exclusion of RNA and Protein

Avery, MacLeod, and McCarty specifically tested the roles of RNA and protein by using enzymes that degraded these molecules before performing the transformation. Their results showed that the transformation did not occur when RNA or protein was destroyed, reinforcing the conclusion that DNA is the sole hereditary molecule responsible for the observed genetic change.