Editing Molecular biology (section)

==Meselson–Stahl experiment==
{{Main|Meselson–Stahl experiment}}
[[File:Meselson-stahl experiment diagram en chiral.svg|thumb|Meselson-Stahl experiment]]
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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 ''[[Escherichia coli|E. coli]]'' bacteria in a medium containing heavy isotope of nitrogen (<sup>15</sup>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 (<sup>14</sup>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 <sup>14</sup>N medium, the DNA formed a band of intermediate density between that of pure <sup>15</sup>N DNA and pure <sup>14</sup>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.