A high-quality sample of DNA is required for a variety of downstream applications, including PCR and sequence. DNA purification is a process that removes contaminants from the sample, for example proteins or other cellular components. This creates a nucleic acid solution that is ready for use. There are a wide variety of DNA purification methods available, each having distinct advantages and disadvantages, depending on the starting material and the intended application.

The initial step in DNA purification is to remove protein from the sample with a protease (proteinase enzyme) or mechanical disruption. After the cellular debris has been removed, the DNA can be precipitated with ethanol to form a white, stringy precipitate. The DNA that is precipitated is placed in a sterile buffer. The concentration of DNA can be determined by spectrophotometry, based on the peak of nucleic acid absorbance at 260nm.

Salting out is a different method for DNA purification. A cellulose column is used for this procedure to capture and attach DNA. The cellulose matrix is cleaned with detergents to eliminate contaminants, and then the wash buffer is used to remove the salts. DNA binds with the matrix in low-salt conditions. The proteins and RNA that have been contaminated are then removed using higher-salt solutions. The eluted RNA and DNA are then recovered by the process of ethanol precipitation.

Anion exchange is also a well-known method for purifying DNA. This method utilizes a cation-exchange resin to attract positively-charged DNA molecules, while neutralizing resins allow negatively charged DNA to be flushed out of the column. Once the DNA is eluted, it can then be concentrated by centrifugation. The DNA can be precipitated out by washing it off with 70 percent ethanol at temperatures that are ice cold.

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