The Meselson-Stahl experiment demonstrated that DNA replication produces new molecules of DNA each containing…

• A. Two old strands of DNA.
• B. Two new strands of DNA.
• C. Two stands composed of variable proportions of old and new DNA.
• D. One old strand of DNA and one new strand of DNA.

Answer: (D)

Verified step by step guidance

1. Understand the context of the Meselson-Stahl experiment, which was designed to determine the method of DNA replication.
2. Recall the three proposed models of DNA replication: conservative, semi-conservative, and dispersive.
3. In the conservative model, the original DNA molecule is conserved, and a completely new molecule is synthesized. In the dispersive model, each strand of both daughter molecules contains a mix of old and new DNA.
4. The semi-conservative model, which was supported by the Meselson-Stahl experiment, suggests that each new DNA molecule consists of one old (parental) strand and one newly synthesized strand.
5. The experiment used isotopic labeling with nitrogen isotopes to distinguish between old and new strands, demonstrating that after replication, DNA molecules contained one strand from the original molecule and one new strand, confirming the semi-conservative model.