NOS-DNA Replication

Obtaining evidence for scientific theories: What evidence did Meselson and Stahl obtain to support the semi-conservative replication of DNA?

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  1. Meselson and Stahl obtained that DNA from cells contained equal amounts of DNA with two different densities, they also obtained that living cells developed a pattern of reproducing the DNA. They concluded that DNA has semi-conservative replication. They placed the bacteria in an environment which contained a selected Nitrogen isotope. They first used N14. The bacteria then integrated this isotope into their DNA. Later they used an environment that contained N15. Afterwards they looked at which of the isotopes the bacterial DNA contained. They found that it contained both isotopes of nitrogen, which implies that conservative replication is not the correct conclusion. By having a closer look they could then also rule out disperse replication. Some helix strands were all N14. Other helix strands from the time in the N15 environment had N15. says The Replication of DNA in Escherichia coli”

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