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In the experimental proof of the replication model of DNA, the medium contained

( a ) cesium chlrode
( b ) ammonium bromide
( c ) ammonium thiosulphate
( d ) ammonium chloride

1 Answer

Ans: (D) ammonium chloride
Meselson and stahl performed the following experimental proof for DNA replication. They grew E.Coli in a medium containing $^{15}NH_4Cl$ as the only $N_2$ source for many generations. The result was $^{15}N$ was incorporated into newly synthesised DNA. This heavy DNA molecule could be distinguished from the normal DNA molecules by centrifugation in a cesium chloride density gradient, Then they transferred the cells into a medium with normal $^{14}NH_4Cl$ and took samples at various definite time intervals as the cells multiplied and extracted DNA that remained as double stranded helices. The various samples were separated independently on CsCl gradients to measure densities.
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