IB Biology SL D1.1.2 Semi Conservative Replication Questions

In semi-conservative replication, each new DNA molecule contains one original strand and one newly synthesized strand. Complementary base pairing copies the sequence accurately; Meselson–Stahl isotope evidence supports this model.

Exam points

Explain that each new DNA molecule contains one original strand and one newly synthesized strand.
Use complementary base pairing on template strands to explain accurate DNA sequence copying.
Use Meselson–Stahl isotope results to identify evidence for semi-conservative replication and distinguish it from conservative replication.

[Maximum number: 1]

Meselson and Stahl grew bacteria in a medium with ${ }^{15} \mathrm{~N}$ (heavy nitrogen) so that all bacteria in the parental culture contain heavy DNA. They then transferred some of the bacteria to a medium with ${ }^{14} \mathrm{~N}$ (light nitrogen).

Samples were taken at 0,20 and 40 minutes and centrifuged with the results as shown.

Figure for Question IB Biology SL D1.1.2 Semi Conservative Replication Questions question 1 — IB Biology SL

State the conclusion Meselson and Stahl drew from their experiment.

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IB Biology SL D1.1.2 Semi Conservative Replication Questions question 1