Ethanol precipitation is a method of DNA extraction from a saline solution. DNA is attracted to positively charged ions in salt, which allows it to easily move away from water when ethanol is added. This method is important for genetic studies.
Ethanol precipitation is a DNA extraction process in which this material is extracted from a saline solution by the addition of ethanol. DNA is a double helix of two negatively charged phosphate-sugar backbones, along which nucleic acids are bound, therefore positively charged ions such as calcium or sodium will be attracted to its backbone. Ionic salts and DNA dissolve easily in water but not as easily in ethanol because both require a polar solvent such as water to dissociate. Adding ethanol to a salty solution then causes the DNA to accumulate and fall out of the solution.
DNA is a polar molecule, and since “like dissolves like,” polar molecules dissolve easily in polar solvents. Although it dissolves easily in water, DNA does not dissolve in a less polar solvent such as ethanol. Ethanol is still a polar molecule, but it has a short, non-polar carbon chain. This slight difference in polarity allows for the precipitation of ethanol based on the inability of DNA to dissolve as easily in ethanol as it does in water.
If an experimenter were to add ethanol directly to a solution of DNA dissolved in water, the molecule would not precipitate. This is because the DNA would still be surrounded by polar water molecules and polar groups on the ethanol which could function as a shield, separating the charged DNA from the ethanol’s uncharged carbon chains. Salt has proven to be a vital factor in the process.
By adding salt to a solution before adding ethanol, the DNA is freed from its dependence on water as a polarity shield. The positive elements in salt, which dissociate and are positively charged ions freely in water, are strongly attracted to the negative charge on the DNA. This attraction of the salt causes the DNA to be attracted to those ions rather than the positive polarity of the water molecules, allowing it to easily move away from the water when a less polar solvent such as ethanol is added.
By allowing calcium or other positively charged ions to be attracted to DNA, then precipitating salt out of solution by decreasing the water content with the addition of ethanol, scientists are provided with a method by which DNA can be extracted from solution . Many studies rely on the isolation and processing of DNA for genetic screens and protein expression, so many experimenters believe that ethanol precipitation has proven to be an invaluable scientific tool.
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