How was a heavy isotope of nitrogen used to provide experimental evidence to semi-conservative mode of DNA replication?

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Solution

Messelson and Stahl (1958) cultured bacteria E. coli in a cultural medium containing 15N isotopes 15NH4 Cl (15N is a heavy isotope of nitrogen) of nitrogen. After the replication of DNA of E. coli for many generations in 15N medium, it was found that both strands of DNA contained 15N as the constituent of purines and pyrimidines.
This heavy DNA molecule could be distinguished from the normal DNA by centrifugation in a cesium chloride (CsCl) density gradient. Being 15N not a radioisotopic isotope, it can be separated from 14N only based on densities.

When these bacteria with incorporated 15N were placed in medium containing 14N (14NH4Cl), it was noticed newly formed DNA molecules contain one Strand heavier than the other. DNA such formed was found to be hybrid as one strand was made up of ‘^N (old) and another was made up of 14N (new).

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Similar questions

Q. Which of the following is the method developed by Matthew Meselson and Franklin Stahl to separate heavy DNA with N

^{15}

from DNA with N

^{14}

, for providing evidence for semi-conservative replication of DNA?

The method developed by Matthew Meselson and Franklin Stahl to separate heavy DNA with N-15 from normal DNA with N-14. So that they can providing evidence for semi-conservative replication of DNA is ____

Q. Meselson and Stahl grew bacteria in the presence of a heavy isotope of nitrogen N

^{14}

. The DNA was then transferred to a growth medium containing nucleotides with a lighter isotope of nitrogen N

^{12}

which then proceeded to replicate.
The DNA was centrifuged to separate it into weight forming bands. After one round of DNA replication, there was one band in the middle of the centrifuge tube. After two rounds of DNA replication in the lighter nitrogen, two separate bands of DNA could be seen. This demonstrated that replication is semi-conservative.
Why do these results support that idea?

Q. Which of the following was used by Meselson and Stahl to separate DNA during their experiment on the semi-conservative nature of DNA replication?

Which particular process was used by Meselson and Franklin in order to study the semi-conservative replication of DNA?

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