Basics of DNA Replication

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How did the scientific community learn that DNA replication takes place in a semi-conservative fashion?


Meselson’s experiments with E. coli grown in 15N deduced this finding.

Imagine the Meselson and Stahl experiments had supported conservative replication instead of semi-conservative replication. What results would you predict to observe after two rounds of replication? Be specific regarding percent distributions of DNA incorporating 15N and 14N in the gradient.


Following two rounds of conservative replication, two bands would be detected after ultracentrifugation. A lower (heavier) band would be at the 15N density, and would comprise 25% of the total DNA. A second, higher (lighter) band would be at the 14N density, and would contain 75% of the total DNA.