DNA Replication and Meselson And Stahl's Experiment

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

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

Experiment

¹⁵N (heavy) and ¹⁴N (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 ¹⁵NH₄Cl over many generations. As a result, ¹⁵N was integrated into the bacterial DNA. Later, they revised the ¹⁵NH₄Cl medium to normal ¹⁴NH₄Cl. At a regular interval of time, they took the sample and checked for the density of DNA.

Observation

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.

Conclusion

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 Replication

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:

• Primarily during this process, two DNA strands will open and separate.

• As the strands are separated, the enzymes start synthesizing the complementary sequence in each of the strands. That is, each parental strand will act as a template for the newly synthesized daughter strands.

DNA Replication

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.

DNA Replication Fork

Also Read: DNA Replication

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