Question

The initial proposal for DNA replication is either conservative or semiconservative (not liberal). In the "most beautiful experiment in biology", Meselson and Stahl proved it is one not the other. This is a seminal discovery that solidified the mechanism of DNA replication and transfer of genetic material. A) briefly describe the experiment and how the conclusion was reached; (2 points) B) What would the experimental result be if DNA replication is conservative? Describe for two rounds of replication starting with one double strand DNA (4 points) C) What would the experimental result be if DNA replication is semiconservative? Describe for two rounds of replication starting with one double strand DNA (4 points)

Answer 1

A.E.coli grown with several generations in a medium having 15N nitrogen.e.coli cell with DNA 15N were transferred to medium having 14N .after one round of replication the results shown of intermediate density so conservative replication idea discarded.dispersive idea also discarded because same strand is not an intermediate of 14N and 15N.

B.if DNA replication is conservative the density will show of only 15N gradient density.all strands remain in bottom itself . first one double strand separate and from each strand only 15N generated from each of the two DNA strands later give rise to another two strands having 15N only.Totally 4 strands generated.

C.The gradient remain in intermediate area.when a parent strand having 15N replicate in a medium having 14 N..newly formed DNA have first strand 15 N and newly formed 14N strand.second round have 15N and 14 N in one DNA double helix and 14 N and 14 N in another helix.