What is the purpose of mixing isolated DNA with ethanol post-isolation?

Mixing isolated DNA with ethanol serves a critical function in the DNA purification process. The primary purpose of this step is to precipitate the DNA out of solution. When ethanol is added to the aqueous solution containing DNA, it decreases the solubility of the DNA due to the change in the polarity of the solution. In the presence of ethanol, DNA molecules aggregate and form a solid mass or precipitate, which can then be collected by centrifugation. This is a crucial step because it allows for the removal of impurities and contaminants that may be present in the original solution, thereby concentrating the DNA for subsequent use.

While enhancing DNA purity, separating proteins, or facilitating visualization could be factors in related processes, the direct and immediate purpose of adding ethanol is specifically to allow the DNA to precipitate, making it easier to recover and purify. This ensures that the DNA is ready for downstream applications such as cloning, sequencing, or other molecular biology techniques.