What is ethanol precipitation?

Ethanol precipitation, also known as alcohol precipitation, is a DNA extraction process by adding ethanol to extract the desired substance from the salt solution DNA is two negatively charged phosphate sugar skeletons, which form a double helix along the nucleic acid bond, so positive ions such as calcium or sodium can be attracted to its skeletons Ionic salts and DNA are easy to dissolve in water, but difficult to dissolve in ethanol, because they need polar solvents such as water to decompose Therefore, adding ethanol to the salt solution will cause DNA to form particles and precipitate out of the solution DNA is a polar molecule According to the principle of similar phase solubility, polar molecules are easy to dissolve in polar solvents Although it is easy to dissolve in water, DNA is not soluble in less polar solvents such as ethanol Ethanol is still a polar molecule, but it has a short nonpolar carbon chain It's this tiny difference in polarity that precipitates ethanol, because DNA doesn't dissolve in ethanol as easily as water If the experimenter added ethanol directly to the solution of dissolved DNA, the molecule would not precipitate This is because DNA is still surrounded by polar molecules of water, and the polar groups on ethanol can act as shields to separate charged DNA from uncharged ethanol carbon chains In this process, salt has been proved to be an important factor Adding salt to the solution before adding ethanol frees DNA from its dependence on water (polar barrier) The positive elements of salt (free and free floating positively charged ions in water) are strongly attracted by negatively charged DNA This salt attraction causes DNA to be attracted by these ions rather than by the positive polarity of water molecules, so it's easy to let it precipitate out of water when adding low polarity solvents such as ethanol By letting calcium or other positively charged ions be attracted to DNA, and then making salt precipitate out of the solution by increasing glycol to reduce water composition, scientists can take DNA out of the solution Many researches rely on DNA separation, gene screening and protein expression processing methods, so many experimenters regard ethanol precipitation as a valuable scientific tool.