Question

Semiconservative mode of replication of $DNA$ was proved by

• A. Hershey and Chase
• B. Griffith
• C. Watson and Crick
• D. Meselson and Stahl

Answer 1

Answer: (D)

Semi-conservative replication of $DNA$ was proved by the work of Mathew Meselson and Fanklin Stahl $(1958)$. They grew $E$. coli in a medium containing ${}^{15}N{H}_{4}Cl$ for many generations. The result was that ${}^{15}N$ was incorporated into newly synthesised $DNA$. Then they transferred the cells into a medium with normal ${}^{14}N{H}_{4}Cl$ and took samples at various definite time intervals, which were analysed through $CsCl$ density gradient centrifugation .The $DNA$ that was extracted from the culture after one generation had a hybrid of intermediate density. $DNA$ extracted from the culture after second generation was composed of equal amounts of this hybrid $DNA$ and of light $DNA$. In this way it was proved that at each replication, one strand of parent $DNA$ is conserved in the daughter while the second is freshly synthesized.