DNA extraction involved 3 steps:1- cell lysis by destruction of cell wall and other membrane. 2- precipitation of protein. 3- recover of DNA and re-precipitate it by isopropanol. you can depend on molecular cloning a laboratory methods 2001 to Sambrook and Russeel for DNA extraction. with my regards
There are multiple methods.For you I will refer Ethanol precipitation,because its easy and have the minimum cost, besides this, there are also many commercial kits to purify DNA ..I AM SURPRISED YOU ASKING ABOUT PURIFICATION AND ALL THE ABOVE COMMENTS ARE ABOUT ISOLATION, STRANGE..
There are many methods indeed to purify DNA but surely depend on the sample source you extract it from. If you are interested in getting pure DNA then you might want to add an RNase treatment to your extraction protocol. Of course the treatment can come together with some extraction kits. Also Ethanol precipitation works best with genomic DNA and reduces the chance of salt contamination in your samples compared with isopropanol precipitation.