Question

You are studying an alien bacteria-like organism isolated from the clouds of Venus. You decide to repeat the Meselson-Stahl experiment to find out how it replicates its DNA. This time you plan to grow the cells on light 14N medium for many generations first. Then, you plan to transfer them to heavy 15N medium and allow them to grow for 2 additional generations (2 rounds of DNA replication). If the alien replicates its DNA via the conservative model of DNA replication, what is the expected distribution of DNA in the density gradient after two rounds of replication

Answer 1

it is expected to observe two bands: one band of light density and one band of heavy density

Step-by-step explanation:

DNA replication is semiconservative because when DNA is replicated both resulting DNA molecules are composed of one original strand and one newly synthesized strand. If DNA replication would be conservative, then the original DNA molecule would serve as a template to produce a new DNA molecule, thereby each cell division would produce one daughter cell with a new DNA molecule and one daughter cell with the original DNA molecule of the parental cell. In this case, the transfer of bacteria-like organisms into a heavy 15N medium would produce two types of DNA cells after replication: cells with original DNA of light density (14N) and cells with new DNA of heavy density (15N), which would be distributed in two bands after centrifugation.