Basics of DNA Replication

Free Response

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

Hint:

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.

Hint:

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.