Transcript Conservative replication

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