Now once we form these E. Coli cells that contain the heavy DNA molecules, these ecology cells are then transferred into a beaker into a flask that contains the regular nitrogen N 14 isotope. And so now when these E. Coli cells are going to reproduce via mitosis, they're going to incorporate the N 14 isotope into the newly synthesized DNA molecules. And what we want to answer is what will be the distribution of the N 14 and N 15 isotopes following several cycles of replication. And based on this, we can basically determine if the semiconservative process actually works. So this experiment has three important points. Number one is the original parental strands contain the N 15 isotopes and that's because they were initially grown in the N 15 rich medium b is or .2 is replicated daughter strands because now the medium is changed to the N 14.