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 concept of DNA replication: DNA replication is the process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules. Each strand of the original DNA serves as a template for the production of the complementary strand.
2. Learn about the Meselson-Stahl experiment: This experiment was designed to determine the method of DNA replication. It used isotopes of nitrogen (N-15 and N-14) to label the DNA and distinguish between old and new strands.
3. Explore the experimental setup: Meselson and Stahl grew E. coli in a medium containing heavy nitrogen (N-15) and then shifted them to a medium with light nitrogen (N-14). They extracted DNA at various intervals and analyzed it using density gradient centrifugation.
4. Analyze the results: After one round of replication, the DNA consisted of hybrid molecules, each containing one strand of N-15 DNA and one strand of N-14 DNA. This indicated that DNA replication is semi-conservative.
5. Conclude the findings: The experiment demonstrated that each new DNA molecule consists of one old strand and one new strand, supporting the semi-conservative model of DNA replication.