Practice question

Alcohol precipitation of DNA exploits solubility differences modulated by dielectric constant. DNA is soluble in water due to hydration of its negatively charged phosphate backbone. Addition of monovalent salt like sodium acetate neutralizes charges, while ethanol or isopropanol, having much lower dielectric constant than water, reduces the shielding of electrostatic interactions, allowing Na+ to bind phosphates. This decreases hydrophilicity and causes DNA to fall out of solution and precipitate. Charge repulsion is overcome, not increased, and pH shift or denaturation is not the primary mechanism for precipitation.