Describe the role of ¹⁵N in the Meselson–Stahl experiment.

Key Concepts

Meselson–Stahl Experiment

The Meselson–Stahl experiment, conducted in 1958, was a pivotal study that demonstrated the semi-conservative nature of DNA replication. By using isotopes of nitrogen, specifically ¹⁵N and ¹⁴N, the researchers were able to trace the incorporation of these isotopes into newly synthesized DNA strands, providing clear evidence of how DNA replicates.

Isotopes and Labeling

Isotopes are variants of elements that have the same number of protons but different numbers of neutrons, resulting in different atomic masses. In the Meselson–Stahl experiment, ¹⁵N, a heavier isotope of nitrogen, was used to label the DNA of bacteria. This labeling allowed scientists to distinguish between old and newly synthesized DNA based on density during centrifugation.

Centrifugation and Density Gradient

Centrifugation is a technique that uses rapid spinning to separate components in a mixture based on their density. In the context of the Meselson–Stahl experiment, the DNA samples were subjected to density gradient centrifugation, which allowed the researchers to observe distinct bands of DNA corresponding to different densities, thus confirming the semi-conservative replication model as the DNA strands separated into light and heavy forms.