Why does 80 ethanol precipitate dna

Masahito Hayashi , 3 Prof. Takahiro Kenmotsu , 1 and Prof. Kenichi Yoshikawa 1. Koichiro Sadakane. Yuko Yoshikawa. Tadayuki Imanaka.

Kingo Takiguchi. Masahito Hayashi. Takahiro Kenmotsu. Kenichi Yoshikawa. Author information Article notes Copyright and License information Disclaimer. Kenichi Yoshikawa, Email: pj. Corresponding author. Received Nov 3. This article has been cited by other articles in PMC. Abstract We observed single DNA molecules at different ethanol concentrations by using fluorescence microscopy. Keywords: DNA structures, ethanol precipitation, phase transitions, single-molecule studies, water nanoclusters.

Open in a separate window. Figure 1. It is possible to place the sample at degC overnight at this stage. Centrifuge at 12, rpm in a microcentrifuge Fisher for 15 minutes at 4 degC, decant the supernatant, and drain inverted on a paper towel.

It is advisable to aliquot the DNA purified in large scale isolations i. Notes on precipitation of nucleic acids A. Place at degC for at least 30 minutes, or at degC overnight.

Mix by inversion and store at degC. This causes the DNA to become less hydrophilic and precipitate out of solution. Ice to chill the sample. Lower temperatures promote the flocculation of the nucleic acids so they form larger complexes that pellet under the centrifugal forces of a microcentrifuge. A nucleic acid concentration high enough to force the DNA out of solution if the concentration is not high enough, you can add a carrier nucleic acid or glycogen to enhance the recovery. DNA is less soluble in isopropanol so it precipitates faster even at low concentrations.

With ethanol, the DNA needs to be at a higher concentration to flocculate but the salt tends to stay soluble, even at colder temperatures. So for the typical precipitation protocol, isopropanol is added from between 0. If you are precipitating small volumes of DNA, and you can fit the required amount of solvent into the sample tube, then ice-cold ethanol is the preferred choice. After precipitation, the nucleic acids can then be separated from the rest of the solution by centrifugation.

After a further centrifugation step, the ethanol is removed and the nucleic acid pellet is allowed to dry before resuspending in a clean aqueous buffer.

First, we need to know why nucleic acids are soluble in water. Water is a polar molecule — it has a partial negative charge near the oxygen atom due to the unshared pairs of electrons, and partial positive charges near the hydrogen atoms.

Because of these charges, polar molecules like DNA or RNA can interact electrostatically with the water molecules, allowing them to easily dissolve in water.

Nucleic acids are hydrophilic due to the negatively charged phosphate PO 3 — groups along the sugar-phosphate backbone. OK, so back to the protocol.