Why precipitate DNA with absolute ethanol?

The DNA was precipitated with absolute ethanol, which is the most commonly used method for precipitating DNA in experiments.The advantage of ethanol is that it can be miscible with water in any ratio. Ethanol and nucleic acid do not react chemically and are safe for DNA, so it is an ideal precipitant.

95% ethanol can also replace absolute ethanol

The DNA solution is stably present in a hydrated state. When ethanol is added, ethanol will deprive water molecules around the DNA, making the DNA dehydrated and easily polymerized. In the general experiment, 2 times the volume of anhydrous ethanol is mixed with the phase, and the final content of ethanol accounts for about 67%. Therefore, 95% ethanol can be used instead of absolute ethanol (because the price of anhydrous ethanol is far more expensive than 95% ethanol). However, adding 95% ethanol increases the total volume, and DNA has a certain degree of dissolution in the solution, so the DNA loss also increases, especially when it is precipitated with multiple times of ethanol, it will affect the yield. The compromise is to use 95% ethanol instead of anhydrous ethanol to precipitate the DNA for the first time. The final precipitation step uses anhydrous ethanol. It is also possible to selectively precipitate DNA with 0.6 volumes of isopropanol. Usually it is allowed to stand at room temperature for 15-30 minutes.