Question

You decide to repeat the Meselson-Stahl experiment, except this time you plan to grow the cells on light 14N medium for many generations and then transfer them to heavy 15N medium and allow them to grow for 2 additional generations (2 rounds of DNA replication). If the conservative model of DNA replication is correct, what is the expected distribution of DNA in the density gradient after one round of replication?

Answer 1

Answer:

One band of light density and one band of heavy density.

Explanation:

According to conservative model of replication, the original strands do not separate from each other during replication. Hence, after replication the old strands are together and the new strands are together.

Here, cells were grown in 14N medium first so 14N was used for DNA replication and all DNA molecules had 14N. When the cells were transferred to 15N medium, only 15N was available for replication process. New DNA molecules would be synthesised using 15N (15N15N) and old DNA molecules have 14N (14N14N). Hence, in density gradient one band will be of light density (14N14N) and one band will be of heavy density (15N15N).