(Solved): 8. DNA replication. Messelson and Stahl first tested the mechanism of DNA replication. They grew ba ...

8. DNA replication. Messelson and Stahl first tested the mechanism of DNA replication. They grew bacterial cells with $${}^{15}{\mathrm{NH}}_4\mathrm{Cl}$$. The DNA contained only "heavy" isotopes $$({}^{15}\mathrm{N}$$ in both DNA strands). They transferred the cells to fresh growth media with $${}^{14}{\mathrm{NH}}_4\mathrm{Cl}$$. As the cells divided, Messelson and Stahl observed that the DNA was converted to a "hybrid" state $$\left({}^{14}\mathrm{N}?{}^{15}\mathrm{N}\right)$$ and then to a "light" state $$\left({}^{14}\mathrm{N}?{}^{14}\mathrm{N}\right)$$. According to the semi-conservative mechanism, what is the percentage of each type of DNA after it is replicated once, twice, and three times?