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

Verified step by step guidance

1. Understand that the Meselson–Stahl experiment was designed to determine the mechanism of DNA replication.
2. Recognize that ¹⁵N is a heavy isotope of nitrogen, which was used to label the DNA of E. coli bacteria.
3. Note that the bacteria were initially grown in a medium containing ¹⁵N, causing their DNA to become 'heavy' due to the incorporation of ¹⁵N into the nitrogenous bases.
4. After several generations, the bacteria were transferred to a medium containing the lighter ¹⁴N isotope, allowing researchers to track the incorporation of ¹⁴N into newly synthesized DNA strands.
5. Realize that the use of ¹⁵N allowed Meselson and Stahl to distinguish between 'heavy' and 'light' DNA using density gradient centrifugation, ultimately demonstrating the semi-conservative model of DNA replication.

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.