Discuss the singnificance of heavy isotope of nitrogen in the Meselson and Stahl's experiment .

Explanation

They performed experiments on E. coli to prove that DNA replication is semi-conservative They first frew the bacteria in a medium containing `.^(15)NH_(4)Cl` (in which `.^(15)NH_(4)Cl` is the heavy istope of nitrogen ) for many generations.
Then performed the cells into a medium with normal `.^(14)NH_(4)Cl` (in which `.^(14)N` is the lighter isotope ) and took the samples at various definite time intervals as the cells multiplied. The extracted DNA were centrifuged and measured to get their densities.
The DNA extracted from the culture after one generation of transfer from them `.^(15)N` medium to `.^(14)N` medium, (i.e., after 20 minutes E. coli divides every 20 minutes) showed an intermediate hybrid density, i.e., both heavy and light nitrogen, which proved the semi-conservative nature of DNA.