In 1958, Messelson and Stahl performed an experiment to establish the mechanism of DNA replication. How were able to distinguish parental DNA from newly made DNA?
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How did Meselson and Stahl show that DNA replication is semiconservative?
How did Meselson and Stahl demonstrate that replication in $E .$ coli takes place in a semiconservative manner?
In the 20th century, scientists conducted an experiment to determine that DNA replication occurred through a semi-conservative mechanism. To demonstrate this, they initially grew E. coli in the presence of a heavy nitrogen isotope (N-15). This heavy nitrogen isotope would be incorporated into any DNA synthesized during this time. They then transferred their bacteria to a solution that contained a light nitrogen isotope (N-14) so that any new DNA synthesized would have N-14 instead of N-15 incorporated. The image below shows a schematic of this, as well as their results for the first two generations. Meselson and Stahl actually allowed their experiment to run for an additional two generations. Explain what the data from the third and fourth generations would look like assuming semi-conservative replication. EXPERIMENTAL SETUP: Generation 0 DNA sample Generation 1 DNA sample Generation 2 DNA sample 15N 14N 14N Cell transfer RESULTS: Top of centrifuge tube (lower density) 14N Hybrid 15N Bottom of centrifuge tube (higher density) After 2 generations: 1/2 low-density DNA 1/2 intermediate-density DNA
Jenny W.
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