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Messelson and Stahl’s experiment supported the semi-conservative mode of replication.

Messelson and Stahl’s experiment supported the semi-conservative mode of replication. The DNA was first replicated in 14N medium which produced a band of 14N and 15N hybrid DNA. This eliminated the conservative mode of replication.

The different modes of replication of DNA are:




Semi-conservative mode of replication produces two copies, each containing one original strand and one new strand. On the contrary, conservative replication produces two new strands and would leave two original template DNA strands in a double helix.

The result of DNA replication is one original strand and one new strand of nucleotides.

If DNA replication goes wrong, a mutation occurs. However, if any mismatch happens, it can be corrected during proofreading by DNA Polymerase.

Literally, replication means the process of duplication. In molecular biology, DNA replication is the primary stage of inheritance. Central dogma explains how the DNA makes its own copies through DNA replication, which then codes for the RNA in transcription and further, RNA codes for the proteins by the translation. Let’s go through Meselson and Stahl Experiment and DNA replication.

Meselson and Stahl Experiment was an experimental proof for semiconservative DNA replication. In 1958, Matthew Meselson and Franklin Stahl conducted an experiment on  E.coli  which divides in 20 minutes, to study the replication of DNA.

Semi conservative DNA Replication through Meselson and Stahl’s Experiment

15 N (heavy) and  14 N (normal) are two isotopes of nitrogen, which can be distinguished based on their densities by centrifugation in Ca,esium chloride (CsCl). Meselson and Stahl cultured E.coli in a medium constituting  15 NH 4 Cl over many generations. As a result,  15 N was integrated into the bacterial DNA. Later, they revised the  15 NH 4 Cl medium to normal  14 NH 4 Cl. At a regular interval of time, they took the sample and checked for the density of DNA.

Sample no. 1 (after 20 minutes): The sample had bacterial DNA with an intermediate density. Sample no. 2 (after 40 minutes): The sample contained DNA with both intermediate and light densities in the same proportion.

Based on observations and experimental results, Meselson and Stahl concluded that DNA molecules can replicate semi-conservatively. Investigation of semi-conservative nature of replication of DNA or the copying of the  cells , DNA didn’t end there. Followed by Meselson and Stahl experiment, Taylor and colleagues conducted another experiment on  Vicia faba  (fava beans) which again proved that replication of DNA is semi-conservative. Also Read:  DNA Structure

DNA is the genetic material in the majority of the organisms.  Structurally, it is a double-stranded helical structure which can replicate. DNA replication is the process by which the DNA makes multiple copies of itself. It was originally proposed by Watson and Crick. DNA replication proceeds as follows:

Since the new DNA strands thus formed have one strand of the parent DNA and the other is newly synthesized, the process is called semiconservative DNA replication.