Deoxyribonucleic Acid, also known as DNA, is the "building blocks" for life. It is shaped like a "twisted ladder". The ladder's vertical supports are composed by a sugar and phosphate, with the rungs formed by bases- adenine, guanine, thymine, and cytosine (or A, G, T, and C). A will always pair with T, and G with C. These pairs arrange themselves in such a manner that they form a chemical message, which dictates how an individual is made. DNA is what makes species unique. As each individual is different, our DNA is different as well. By extracting DNA from cells, one can map and sequence DNA, clone and compare it, or even test for a predisposition to certain genetic diseases or traits.
Procedure
- Chew on cheeks to loosen cells- it is not necessary to draw blood.
- Rinse with saline solution to keep the cells from bursting open prematurely.
- After spitting saline solution and saliva into a vial, add lysis buffer to the sample to burst the cell. Lysis buffer works on a cell the same way detergent works on a stain- it dissolves the walls, allowing the contents to flow freely.
- Add protease (an enzyme) to break down proteins. DNA is wrapped around proteins like thread around a spool, so destroying the protein allows it to unravel. Protease will also kill DNase. DNase exists in the cytoplasm to kill foreign DNA from viruses, but because of this, the cell's own DNA is confined to the nucleus. If the DNase wasn't destroyed by the protease, it would kill the DNA before we had the chance to isolate it.
- Add salt. DNA is negatively charged, so it would dissolve in the solution. Adding salt will neutralize it, making it hydrophobic (water-fearing) instead of hydrophilic (water-loving). This will also cause the DNA to clump together, rather than being spread out in the solution.
- Place the vial in a hot-water bath. This will speed up the reaction that breaks the cell membranes.
- Add cold ethanol to precipitate the DNA, as well as keep it from dissolving. Other molecules in the sample will not precipitate, and therefore not be visible.
