DNA molecules in water solution are solvated by H2O molecules, which interact with nucleic acids through hydrogen bonds. In particular, each H2O molecule can be involved in up to 4 H-bonds interactions.
These interactions between DNA and water allow DNA (and more in general any hydro-soluble molecule) to stay in solution. Ethanol (CH3CH2OH), and more in general alcohols (R-OH) have only one hydroxyl group that can be involved in H-bonding.
When an alcohol substitutes water in solution, it displaces the H2O molecules of the DNA solvation shell leading to precipitation, because the DNA no longer properly interacts with the surrounding solvent.
DNA molecules in water solution are solvated by H2O molecules, which interact with nucleic acids through hydrogen bonds. In particular, each H2O molecule can be involved in up to 4 H-bonds interactions.
These interactions between DNA and water allow DNA (and more in general any hydro-soluble molecule) to stay in solution. Ethanol (CH3CH2OH), and more in general alcohols (R-OH) have only one hydroxyl group that can be involved in H-bonding.
When an alcohol substitutes water in solution, it displaces the H2O molecules of the DNA solvation shell leading to precipitation, because the DNA no longer properly interacts with the surrounding solvent.