DNA Extraction

DNA Extraction is typically the first step in a longer laboratory process. DNA first needs to be purified away from proteins and other cellular contaminants.

So Where do we begin?

We first need to collect cell from the test subject. The skin inside of our mouths losses thousands of cells everyday. These cells are ideal for DNA Extraction. Once the “Cheek Cells” are collected you will need to place the swab used for collection in a Eppendorf Tube

Now using a Micropipette, add Lysis a solution with the greek meaning “to separate” into the Eppendorf tube containing the swap used to collect the cheek cells. Once the Lysis has been added you will need to place the tube in a “Warm Water Bath Machine”.
The Lysis solution we just added contains two important ingredients, the first being “Detergent” and the second being “Proteinase K”. The Detergent disrupts the cel membrane and nucleus envelope. Causing the cells to burst open and release their DNA. The DNA is still wrapped very tightly around proteins called histones, and the Proteinase K cuts apart the histones to free the DNA.

The cells have now been in warm water long enough (the cells themselves are not in warm water but merely the Eppendorf tube is) for the DNA freed from the cells, and we have removed the swab from the tube.

Now we must add concentrated salt to the Eppendorf tube containing the DNA. The salt causes the proteins and the cellular debris to clump together. To complete this process we must now place the Eppendorf tube into a centrifuge. In order the balance the centrifuge we have to add a second Eppendorf tube into it that contains only water on the opposite side of the tube containing the DNA sample.

Inside the centrifuge, the tube spin a high speed. The heavy clumps and cellular debris sink to the bottom of the tube, while the DNA strands stays distributed in the liquid above .

Now using a Micropipette we must very carefully remove the liquid above (which contains DNA) the debris and cellular contaminants and place it into a new clean Eppendorf tube, the debris and cellular contaminants will be left behind since they are no longer needed.

Now we will need to add Isopropyl into the Eppendorf tube containing the DNA strands, Inverting the tube several times mixes the Isopropyl alcohol into the DNA solution. Because DNA is not soluble, in Isopropyl alcohol it comes out of the solution. We will then be able to see the DNA with your naked eye.

Again we will have to place the tube into a centrifuge. This time after the sample spins in the centrifuge, the DNA sinks to the bottom of the Eppendorf tube.

Now what’s next? Nothing. The solution left in the tube is the final part of the DNA extraction. Depending on the circumstances you may want to let the solution dry out so it could be frozen for later use, for years even. This can now be used in another forensic laboratory investigation to match that DNA with other DNA found at a crime scene for example.