Question

The experiments of Meselson and Stahl

(A) Were done using viruses
(B) Took advantage of two isotopes of nitrogen
(C) Used gel electrophoresis to separate "heavy" and "light" DNA
(D) All of the above

Answer 1

Meselson and Stahl's experiments used two isotopes of nitrogen, 15N and 14N, to provide evidence of semi-conservative DNA replication in E. coli.

Step-by-step explanation:

The experiments conducted by Meselson and Stahl took advantage of two isotopes of nitrogen, 15N and 14N, to explore the mechanism of DNA replication. They grew E. coli in a medium containing the 'heavy' isotope 15N, which was incorporated into the bacteria's DNA, making it denser. After several generations, the bacteria were switched to a medium with the 'lighter' isotope 14N.

Upon centrifugation, the DNA that was replicated after one round of cell division showed a density halfway between DNA containing only 15N or only 14N, indicating a pattern consistent with semi-conservative DNA replication. Therefore, the correct answer to the student's question is (B) Took advantage of two isotopes of nitrogen.