Question

Using the technique shown below, Meselson and Stahl did an experiment where they grew cells in heavy medium for many generations, then after a single generation in light medium, they observed a single band of intermediate weight after centrifugation. This experiment ruled out which model of DNA replication?

A. conservative

B. semiconservative

C. dispersive

D. liberal

Answer 1

The experiment by Meselson and Stahl, in which E. coli cells were grown in heavy and then light nitrogen, revealed a single band of DNA of intermediate density. This finding ruled out the conservative model of DNA replication.

Step-by-step explanation:

Using the experimental technique developed by Meselson and Stahl, where E. coli was grown in a medium containing heavy nitrogen (15N) and then transferred to light nitrogen (14N), after a single generation, a single band of intermediate weight DNA was observed on centrifugation. This result eliminated the conservative model of DNA replication. If the conservative model had been correct, two bands would have been observed, one consisting of all-heavy (15N) DNA and one consisting of all-light (14N) DNA. Instead, the single intermediate band indicated that DNA strands were composed of a mix of 15N and 14N, which is consistent with the semi-conservative model, where each new DNA molecule consists of one old and one new strand.