If the mechanism of DNA replication MesselsonStahl experimen

If the mechanism of DNA replication (Messelson-Stahl experiment model: semi-conservative, conservative, and dispersive) was not yet known:  

a. What experiment(s) could distinguish between the three possible mechanisms. Explain how this method can distinguish between the 3 models.

b. Compare your experiment with the original (Messelson-Stahl) mechanism. What are the advantages, disadvantages to each?

Solution

After the DNA double helix was discovered by Watson and Crick, there were many hypothetical speculations as to how the double-stranded helix replicated and produced daughter DNA strands. The three possibility were as follows:

a. If these three models of DNA replication were not yet known, then an experiment could be designed as follows:

After replication, the DNA products can be isolated, fluorescently tagged and chromatin fiber assay could be carried out using fluorescent microscopy. The DNA daughter strands produced by semi-conservative mode can be visualized by such experiment.

b. Advantage:

With the advent of new cell biology techniques and high-end microscopy, chromatin fiber assay is efficient to visualize the mode of replication of DNA. As compared to Messelson-Stahl experiment, the need for culturing bacterial cells generations after generations is not required.

Disadvantage:

Messelson and Stahl\'s experiment is a classic and time-tested experiment which was simple and direct. Newer techniques such as the chromatin fiber assay might not be suitable for all organisms and also prove to be complicated and expensive.