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Meselson-Stahl Experiment quiz

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  • What is the main conclusion of the Meselson-Stahl experiment?
    The experiment confirmed that DNA replicates via the semi-conservative model, where each new DNA molecule contains one old strand and one new strand.
  • Which organism did Meselson and Stahl use in their experiment?
    They used the bacterium Escherichia coli (E. coli).
  • What isotopes of nitrogen were used in the Meselson-Stahl experiment?
    Nitrogen-15 (N-15) and Nitrogen-14 (N-14) were used to label DNA strands.
  • How does the semi-conservative model of DNA replication work?
    Each new DNA molecule consists of one parental (old) strand and one newly synthesized strand.
  • What did the conservative model of DNA replication propose?
    It proposed that the original DNA molecule is fully conserved and a completely new molecule is synthesized.
  • Why was the dispersive model of DNA replication rejected?
    Because the experiment showed that DNA strands were not a mix of old and new segments, but rather one old and one new strand.
  • How were old and new DNA strands distinguished in the experiment?
    Old strands were labeled with N-15 (dark blue), and new strands were labeled with N-14 (light blue).
  • What was the result after one round of replication in N-14 medium?
    DNA molecules contained one strand with N-15 and one with N-14, supporting the semi-conservative model.
  • What does the term 'semi-conservative' mean in the context of DNA replication?
    It means that each replicated DNA molecule contains one original (parental) strand and one new strand.
  • What did Meselson and Stahl do after growing E. coli in N-15 medium?
    They switched the bacteria to N-14 medium to track the incorporation of new nitrogen into DNA.
  • How did the results of the experiment disprove the conservative model?
    The results did not show completely old or completely new DNA molecules, as the conservative model predicted.
  • What did further rounds of replication in N-14 medium show?
    They continued to support the semi-conservative model, with each new DNA strand pairing with an old strand from the previous generation.
  • What role did the old parental DNA strands play during replication?
    They separated and acted as templates for the synthesis of new complementary DNA strands.
  • Why is the Meselson-Stahl experiment considered a classic in molecular biology?
    Because it provided clear experimental evidence for the mechanism of DNA replication.
  • What is the key takeaway from the Meselson-Stahl experiment?
    DNA replicates in a semi-conservative manner, with each new molecule containing one old and one new strand.