DNA Extraction
DNA Extraction | Multimedia | Activities
DNA can be extracted from any living organism. During CSIRO’s workshops, wheat germ is often used. In this example the DNA is being extracted from plant cells, which have a cell wall surrounding the cell membrane.
The first step of a DNA extraction is breaking up the wheat germ into small pieces. You are breaking the cell wall here and also increasing the exposure of the plant cells to the chemicals/liquids that you will be adding in. This can be done manually, but in classroom settings is most effectively achieved using a kitchen blender.
The wheat germ is combined with a ionic detergent (Triton X-100) that further breaks down cell membranes, and a buffering agent containing MgCl2 and NaCl. These chemicals cause the breakdown of the cell membrane.
After this step, the cells have been broken up, so that the organelles and cytoplasm are not restrained and are dissolved in the solution. A centrifuge is used to spin the wheat germ solution quickly, and separates the denser organelles from the lighter organelles and cytoplasm.
The nucleus, where DNA is found, is heavy and therefore sinks into the pellet, or bottom, of the tube after centrifuging. The liquid top of the tube, the supernatant, contains the lighter organelles and cytoplasm of the cells. It can be poured off and discarded.
Next, an ionic detergent must be added to break up the nucleus. A common detergent is sodium dodecyl sulfate (SDS). Once the SDS is added to the pellet, the tube is mixed (the pellet is resuspended into the SDS) and then centrifuged again.
During this step, the heavy pieces of broken-up nucleus, as well as other organelles still intact, move to the bottom of the tube and form the pellet, and the DNA dissolves into the liquid supernatant.
In order to precipitate the DNA out of the supernatant, ethanol is added to the mixture. As the ethanol flows into the supernatant, a band of white, string-like DNA will precipitate out at the interface (that is, the point where the ethanol meets the detergent mixture).
The first step of a DNA extraction is breaking up the wheat germ into small pieces. You are breaking the cell wall here and also increasing the exposure of the plant cells to the chemicals/liquids that you will be adding in. This can be done manually, but in classroom settings is most effectively achieved using a kitchen blender.
The wheat germ is combined with a ionic detergent (Triton X-100) that further breaks down cell membranes, and a buffering agent containing MgCl2 and NaCl. These chemicals cause the breakdown of the cell membrane.
After this step, the cells have been broken up, so that the organelles and cytoplasm are not restrained and are dissolved in the solution. A centrifuge is used to spin the wheat germ solution quickly, and separates the denser organelles from the lighter organelles and cytoplasm.
The nucleus, where DNA is found, is heavy and therefore sinks into the pellet, or bottom, of the tube after centrifuging. The liquid top of the tube, the supernatant, contains the lighter organelles and cytoplasm of the cells. It can be poured off and discarded.
Next, an ionic detergent must be added to break up the nucleus. A common detergent is sodium dodecyl sulfate (SDS). Once the SDS is added to the pellet, the tube is mixed (the pellet is resuspended into the SDS) and then centrifuged again.
During this step, the heavy pieces of broken-up nucleus, as well as other organelles still intact, move to the bottom of the tube and form the pellet, and the DNA dissolves into the liquid supernatant.
In order to precipitate the DNA out of the supernatant, ethanol is added to the mixture. As the ethanol flows into the supernatant, a band of white, string-like DNA will precipitate out at the interface (that is, the point where the ethanol meets the detergent mixture).