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DNA isolation is a process of purification of DNA from sample using a combination of physical and chemical methods. The first isolation of DNA was done in 1869 by Friedrich Miescher. Currently it is a routine procedure in molecular biology or forensic analyses. == Basic procedure of DNA extraction == There are three basic and two optional steps in a DNA extraction: * Breaking the cells open, commonly referred to as cell disruption or cell lysis, to expose the DNA within. This is commonly achieved by chemical and physical methods-blending, grinding or sonicating the sample. * Removing membrane lipids by adding a detergent or surfactants which also serves in cell lysis. * Removing proteins by adding a protease (optional but often done). * Removing RNA by adding an RNase (almost always done). * DNA purification from detergents, proteins, salts and reagents used during cell lysis step. The most commonly used procedures are: * * Ethanol precipitation usually by ice-cold ethanol or isopropanol. Since DNA is insoluble in these alcohols, it will aggregate together, giving a ''pellet'' upon centrifugation. Precipitation of DNA is improved by increasing of ionic strength, usually by adding sodium acetate. * * Phenol–chloroform extraction in which phenol denatures proteins in the sample. After centrifugation of the sample, denaturated proteins stay in organic phase while aqueous phase containing nucleic acid is mixed with the chloroform that removes phenol residues from solution. (Note: for DNA isolation in used phenol buffered to pH 8, RNA must be isolated using acidic phenol.) * * Minicolumn purification that relies on the fact that the nucleic acid may bind (adsorption) to the solid phase (silica or other) depending on the pH and the salt content of the buffer. Refinements of the technique include adding a chelating agent to sequester divalent cations, such as Mg2+ and Ca2+, which prevents enzymes like DNase from degrading the DNA. Cellular and histone proteins bound to the DNA can be removed either by adding a protease or by having precipitated the proteins with sodium or ammonium acetate, or extracted them with a phenol-chloroform mixture prior to the DNA-precipitation. After isolation, the DNA is dissolved in slightly alkaline buffer, usually in the TE buffer, or in ultra-pure water. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「DNA extraction」の詳細全文を読む スポンサード リンク
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