Meselson-Stahl Experiment

By Elisa, Andrea, and Allison

Meselson-Stahl Experiment

Meselson-Stahl Experiment

• Steps in the experiment:1. Bacteria was grown in a mediums with heavy isotope of

nitrogen, 15N. 2. The 15N become integrated into the bases, making the DNA

in the bacteria heavier. 3. The bacteria grown with 15N was then moved into a

medium with 14N. 4. Samples of bacteria were periodically taken out. 5. The DNA in these samples was extracted.

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.

Meselson-Stahl Experiment

6. The DNA with 15N was heavier and denser than the DNA with 14N.

7. The DNA was dissolved in cesium chloride and spun in a centrifuge, and so separated the DNA strands by their density

8. The cesium ions moved toward the bottom of the centrifuge tube, and so was denser at the bottom.

9. The DNA moved toward the bottom until their density was equal to the density of cesium ions.

Meselson-Stahl Experiment

• Results: DNA replicates semiconservatively