Meselson-Stahl Experiment

1. Meselson-Stahl Experiment By Elisa, Andrea, and Allison

2. Meselson-Stahl Experiment

3. Meselson-Stahl Experiment • Steps in the experiment: • Bacteria was grown in a mediums with heavy isotope of nitrogen, 15N. • The 15N become integrated into the bases, making the DNA in the bacteria heavier. • The bacteria grown with 15N was then moved into a medium with 14N. • Samples of bacteria were periodically taken out. • The DNA in these samples was extracted.

4. Meselson-Stahl Experiment • There were three types of theories on DNA replication: semiconservative, conservative, and dispersive. • Meselson’s and Stahl’s experiment proved that DNA replication was semiconservative. • Conservative replication would leave the original DNA molecule together, yet create a new molecule. • Dispersive replication would produce two DNA molecules with sections of both old and new DNA along each strand. • Semiconservative replication would be made of both old and new DNA, with each molecule composed of one old strand and one new strand.

5. Meselson-Stahl Experiment • The DNA with 15N was heavier and denser than the DNA with 14N. • The DNA was dissolved in cesium chloride and spun in a centrifuge, and so separated the DNA strands by their density • The cesium ions moved toward the bottom of the centrifuge tube, and so was denser at the bottom. • The DNA moved toward the bottom until their density was equal to the density of cesium ions.

6. Meselson-Stahl Experiment • Results: DNA replicates semiconservatively

8. Bazinga!