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Be sure to answer all parts. Imagine conducting the Meselson and Stahl experiment on DNA that is replicated by the dispersive mechanism. After 3 rounds of replication, what percentage of the DNA would contain exclusively 15N, exclusively 14N, or a mix of 14N and 15N?

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craigsbarbara

Answer:

25% mixture of N15 and N14 and 75% of exclusively N14.

Explanation:

In the Meselson and Stahl experiment a double DNA chain formed by N15 is placed in a medium with only N14. Therefore, when replicated, the new chains will be synthesized with N14 (lighter). This can be corroborated by centrifuging the sample.

Before replication, a single band corresponding to the double helix of N15 DNA is observed.

After a single replication, only one band corresponding to DNA is observed with 1 strand N15 and 1 strand N14.

After the second replication, two bands will be observed. One for DNA of 1 strand N15 and 1 strand N14 and the other for DNA of 2 strands N14.

The same will happen for the third replication. At this point, the DNA present will consist of a 25% mixture of N15 and N14 and 75% of exclusively N14.

This experiment proves that DNA replication is semi-conservative.

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