Question

How did the scientific community learn that DNA replication takes place in a semi-conservative fashion?

Short answer

Thus, Meselson and Stahl's classic experiment conclusively demonstrated that DNA replication is semi-conservative rather than dispersive or conservative.

Step-by-step solution

Step:1 Introduction

Meselson and Stahl conducted an experiment in 1958 to confirm the replication method of DNA. They cultured E.coli bacteria in the presence of heavy nitrogen 15 N, which is incorporated into nitrogenous bases and eventually into DNA.

Step:2 Explanation of the solution

The DNA was labelled with heavy nitrogen (15 N) and then allowed to replicate in a medium containing 14 N. After a few generations, the DNA was separated and centrifuged at high speeds (50,000 to 60000 rpm) using Cesium chloride. The DNA formed bands in the centrifuge tube based on density, which were recognised using an ultraviolet absorption pattern. The DNA sample from 15 N had a larger density band than the DNA sample from 14 N grown in the medium. Meselson and Stahl discovered that one cell generation after transfer to culture medium, a DNA sample revealed a single band with uniform homogeneous density between the bands created by 15 N DNA and 14 N DNA, indicating that after the first generation, all DNA detected has an intermediate density. DNA replicates in a semi-conservative manner, according to these findings.