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 translation.

Let’s go through DNA replication and Meselson and Stahl’s Experiment.

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

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

DNA Replication Fork

Also Read: DNA Replication

Meselson and Stahl’s Experiment

Meselson and Stahl’s 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.

DNA Replication

Semi-Conservative DNA Replication

Experiment

15N (heavy) and 14N (normal) are two isotopes of nitrogen which can be distinguished based on their densities by centrifugation in cesium 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 semiconservative 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 semiconservative.

Also Read: DNA Structure

For more information on DNA Replication and Messelson and Stahl’s experiment, keep visiting BYJU’S website or download BYJU’S app for further reference.

Frequently Asked Questions

Which mode of replication did the Messelson and Stahl’s experiment support?

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.

What are the different modes of replication of DNA?

The different modes of replication of DNA are:

  • Semiconservative
  • Dispersive
  • Conservative

How are semiconservative and conservative modes of replication different?

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.

What is the result of DNA replication?

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

What happens if DNA replication goes wrong?

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

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