Answer and Explanation:
If DNA replication were conservative instead of semi-conservative, the density of DNA molecules and the relative proportions isolated from E. coli cells after two generations in the Meselson/Stahl experiment would be different. In the Meselson/Stahl experiment, conservative replication refers to the complete synthesis of a new DNA double helix, leaving the original parental DNA intact.
Here's an illustration of the expected results:
Generation 0:
- The original DNA molecules in E. coli cells have a density of "heavy" (labeled H) because they were grown in a medium containing a heavy isotope of nitrogen (^15N).
Generation 1:
- After one generation of replication, the conservative model predicts that the two newly synthesized DNA molecules would have a density of "light" (labeled L) because they were synthesized using a medium containing a light isotope of nitrogen (^14N).
- The original parental DNA molecules would still have a density of "heavy" (labeled H) as they were not involved in replication.
Generation 2:
- In the second generation, if replication were conservative, the original parental DNA molecules (labeled H) would still be intact and remain separate from the newly synthesized DNA molecules (labeled L).
Overall, after two generations, the isolated DNA samples would contain a mixture of parental DNA (heavy, H) and newly synthesized DNA (light, L). The relative proportions of the two types of DNA would depend on the efficiency of replication, but they would not be in equal fractions as in the case of semi-conservative replication.
It is important to note that the Meselson/Stahl experiment actually confirmed the semi-conservative model of DNA replication, not the conservative model. The experiment demonstrated that DNA replication is semi-conservative, with each newly synthesized DNA molecule consisting of one parental strand and one newly synthesized strand.