The Meselson-Stahl experiment was a landmark experiment in molecular biology that provided evidence for the semiconservative replication of DNA. Conducted in 1958 by Matthew Meselson and Franklin Stahl, the experiment involved growing E. coli bacteria in a medium containing heavy isotope of nitrogen (N) for several generations. This caused all the newly synthesized bacterial DNA to be incorporated with the heavy isotope.
After allowing the bacteria to replicate in a medium containing normal nitrogen (N), samples were taken at various time points. These samples were then subjected to centrifugation in a density gradient, which separated the DNA molecules based on their density.
The results showed that after one generation of replication in the N medium, the DNA formed a band of intermediate density between that of pure N DNA and pure N DNA. This supported the semiconservative DNA replication proposed by Watson and Crick, where each strand of the parental DNA molecule serves as a template for the synthesis of a new complementary strand, resulting in two daughter DNA molecules, each consisting of one parental and one newly synthesized strand.
The Meselson-Stahl experiment provided compelling evidence for the semiconservative replication of DNA, which is fundamental to the understanding of genetics and molecular biology.