precipitate, allowing the nucleic acid to be separated. Ethanol precipitation Ethanol precipitation is a widely used method for purifying and concentrating nucleic acids, including plasmid DNA. The basic principle of this method is that nucleic acids are insoluble in ethanol or isopropanol but soluble in water. Therefor, it works by using ethanol as an antisolvent of DNA, causing it to precipitate out of solution and then it can be collected by centrifugation. The soluble fraction is discarded to remove other biomolecules. Spin column Spin column-based nucleic acid purification is a method of purifying DNA, RNA or plasmid from a sample using a spin column filter. The method is based on the principle of selectively binding nucleic acids to a solid matrix in the spin column, while other contaminants, such as proteins and salts, are washed away. The conditions are then changed to elute the purified nucleic acid off the column using a suitable elution buffer. Phenol–chloroform extraction The basic principle of the phenol-chloroform extraction is that DNA and RNA are relatively insoluble in phenol and chloroform, while other cellular components are relatively soluble in these solvents. The addition of a phenol/chloroform mixture will dissolve protein and lipid contaminants, leaving the nucleic acids in the aqueous phase. It also denatures proteins, like DNase, which is especially important if the plasmids are to be used for enzyme digestion. Otherwise, smearing may occur in enzyme restricted form of plasmid DNA. Beads-based extraction In beads-based extraction, addition of a mixture containing magnetic beads commonly made of iron ions binds to plasmid DNA, separating them from unwanted compounds by a magnetic rod or stand. The plasmid-bound beads are then released by removal of the magnetic field and extracted in an elution solution for down-stream experiments such as transformation or restriction digestion. This form of miniprep can also be automated, which increases the conveniency while reducing mechanical error. References Further reading External links http://www.protocol-online.org/prot/Molecular_Biology/Plasmid/Miniprep/ A miniprep procedure using diatomaceous earth to bind DNA during purification and washing. Biological techniques and tools Genetics techniques Molecular biology