Structural Biochemistry/Precipitation of Nucleic Acids With Alcohols

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In order to concentrate DNA and remove detergents, salts, and other low molecular weight contaminants from our synthesized DNA, Alcohol precipitation is used. The nucleic acids will not precipitate if there is a monovalent cation to neutralize the negative charges and permit the DNA to aggregate. Na or Cl acetate are most often used in the lab to precipitate DNA because it can also serve as a buffer around PH 5.2. which provide an acidic environment that favors precipitation of DNA. NH4 acetate will be use when there are free deoxynucleotide since they co-precipitate less with NH4 than with Na or Cl. After adding salts, isopropanol or ethanol will be added to reduce solubility which will favor DNA precipitation. Alcohol will form hydrogen bonds with water, in other words, reduces the amount of water for dissolved substance. In addition, the polarizability, or capacity of alcohols to shield opposite charges (keep them away from each other) is less than that of water.