Ethanol precipitation
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2008-06-18T19:29:09Z
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'''Ethanol precipitation''' is a method used to concentrate [[DNA]]. DNA is [[chemical polarity|polar]] and soluble in water because water is polar. Based on the principle of [[Solubility#Polarity|"like dissolves like"]], it is insoluble in the relatively [[nonpolar]] [[ethanol]].
DNA is initially precipitated by adding a large volume of 100% ethanol, and cooling on ice or dry ice. This will precipitate DNA, as well as the [[salts]] that form [[ionic bond]]s with it. The suspension is [[laboratory centrifuge |centrifuged]] in a microcentrifuge tube at high speeds (~12,000[[standard gravity|g]]), and the supernatant solution removed, leaving a ''pellet'' of the crude DNA. The DNA precipitation in this step is due to the ethanol interacting with the water such that fewer water molecules are available to dissolve the DNA molecules.
In the next step, 70%-80% ethanol is added to the precipitated pellet, and is gently mixed to resuspend the DNA. This allows the 20-30% water to access the salts present in the pellet. This suspension is centrifuged again, and the supernatant solution is removed. This step is repeated once.
Finally, the pellet is air-dried giving the purified DNA.
[[Isopropanol]] can be used instead of ethanol; the precipitation efficiency of the isopropanol is higher. However, isopropanol is less volatile than ethanol and needs more time to air-dry in the final step.
======Method======
1) Add 1/10 volume of Sodium Acetate.
2) Add 2.5x volume of 100% ethanol.
3) Incubate at -80 degrees Celsius for 15 minutes.
4) Centrifuge at 14,000 RPM for 30 minutes at 4 degrees Celsius.
5) Rinse with 70-80% EtOH
== See also ==
*[[DNA extraction]]
==References==
{{Unreferenced|date=December 2007}}<references/>
[[Category:Laboratory techniques]]
[[Category:Molecular biology]]
[[ja:エタノール沈殿]]
[[ur:ایتھانولی ترسیب]]