DNA extraction is a combination of chemical and physical separation methods in order to purify a particular DNA from a sample. The addition of salt in the solution is added after the DNA is exposed via cell lysis. The main purpose of adding salt to the solution where the DNA is located is to neutralize its negative charge. The sugar phosphate (`PO_3 ^-` ) backbone is where the positive charge of the salt (usually `Na^(+)` from sodium chloride or table salt) will attach itself and eventually become less hydrophilic and eventually easier to be separated. As the DNA molecules are neutralized, they will be able to stick to each other and then precipitate. NaCl (sometimes with the use/help of surfactant) stabilizes the double helix structure of the DNA.