DNA extraction is a routine procedure to collect DNA for subsequent molecular or forensic analysis. There are three basic steps in a DNA extraction:
1. Breaking the cells open to expose the DNA within, such as by grinding or sonicating the sample.
2. Removing membrane lipids by adding a detergent.
3. Precipitating the DNA with an alcohol — usually ethanol or isopropanol. Since DNA is insoluble in these alcohols, it will aggregate together, giving a pellet on centrifugation. This step also removes alcohol-soluble salt.
Refinements of the technique include adding a chelating agent to sequester divalent cations such as Mg2+ and Ca2+. This stops dnase enzymes from degrading the DNA.
Cellular and histone proteins bound to the DNA can be removed prior to its precipitation either by adding a protease or having prior to precipitation, precipitating with sodium or ammonium acetate, or extracting with a phenol-chloroform mixture.
If desired, the DNA can be resolubilized in a slightly alkaline buffer.
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