Question

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 ____

• A. Ion exchange chromatography
• B. Density gradient centrifugation
• C. Buoyant density centrifugation
• D. Gel filtration
• E. Isopycnic centrifugation

Answer 1

The correct option is B Density gradient centrifugation

In 1957, Meselson and Stahl gave experimental evidence for semi-conservative replication. It was done as follows: -

• E. coli was grown in a medium having a heavy isotope of nitrogen i.e. ${}^{15}N$ nitrogen (heavy).
• Then it was grown on a medium having ${}^{14}N$ nitrogen (light) and after one, two, or three generations the DNA samples were tested.
• They were mixed with caesium chloride and it was centrifuged.
• After one generation, the double-stranded DNA was found to form a band at an intermediate position between the bands of DNA having ${}^{15}N$ nitrogen below it and ${}^{14}N$ nitrogen above it.
• Hence the separation was according to the density of the DNA strand.

Thus the correct answer is option C.