Question

In the first part of the dna isolation, you discarded the supernatant and kept the cells. however, after processing the sample with chelex, you kept the supernatant and discarded the pellet. tracing the path of your dna, explain the goal of each processing step.

Answer 1

For the first step, you must isolate the cells from the media. The cells contain the DNA so you keep the cells and pellet. The next step would be a cell lysis which causes the cells to open and the DNA to come out. At this point you would keep the supernatant, as the pellet is the cell membrane and other parts of the cell. The chelex is to bind to transition metal ions. This would cause and DNases in the cell to become inactive because the metal ion is their cofactor. The pellet in this case would contain the chelex and the DNA would still be in the supernatant.