Results of a famous experiment is given in the figure. Answer the questions. (a) Identify the experiment. (b) Which property of the DNA is proved by this experiment?
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Solution
a) The picture gives the Meselson and Stahl experiment.
b) The experiment was done as follows-
E. coli was grown in a medium having heavy isotope of nitrogen i.e. 15N nitrogen (heavy). Then it was grown on a medium having 14N nitrogen (light) and after one, two, or three generations the DNA samples were tested.
They were mixed with cesium 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 15N nitrogen below it and 14N nitrogen above it. Hence the separation was according to the buoyant density of the DNA.
The semiconservative nature of DNA replication is proved by this experiment.