Ruth C

• 2 + 7 = 9.
• 11 – 3 = 9.
• 2021 + 1 = 2022.

DNA and RNA are hydrophilic (water-loving) molecules and, therefore, soluble in water. Ethanol precipitation of DNA and RNA works by adding salt and ethanol to a DNA solution, which makes the DNA less hydrophilic, causing it to precipitate out.

Ethanol precipitation is a commonly used technique for concentrating and de-salting nucleic acid (DNA or RNA) preparations in an aqueous solution.

The basic procedure is that salt and ethanol are added to the aqueous solution, which forces the precipitation of nucleic acids out of the solution. After precipitation, the nucleic acids can then be separated from the rest of the solution by centrifugation. The pellet is then washed in cold 70% ethanol. 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.

So how does this work?

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. Polar molecules can therefore be described as hydrophilic and non-polar molecules, which can’t easily interact with water molecules, are hydrophobic. Nucleic acids are hydrophilic due to the negatively charged phosphate (PO4–) groups along the sugar-phosphate backbone.

OK, so back to the protocol. The role of salt in the protocol is to neutralize the charges on the sugar-phosphate backbone. A commonly used salt is sodium acetate. In solution, sodium acetate breaks up into Na+ and –. The positively charged sodium ions neutralize the negative charge on the PO4– groups on the nucleic acids, making the molecule far less hydrophilic and, therefore, much less soluble in water.

The electrostatic attraction between the Na+ ions in solution and the PO4– ions are dictated by Coulomb’s Law, which is affected by the dielectric constant of the solution. Water has a high dielectric constant, which makes it fairly difficult for the Na+ and PO4– to come together. Ethanol, on the other hand, has a much lower dielectric constant, making it much easier for Na+ to interact with the PO4–. This shields its charge and makes the nucleic acid less hydrophilic, thus causing it to drop out of the solution.

Incubation of the nucleic acid/salt/ethanol mixture at low temperatures (e.g. –20° or –80°C) is commonly cited as a necessary step in protocols. However, according to Maniatis et al. (Molecular Cloning, A Laboratory Manual 2nd Edition… 2nd edition?? – I need to get a newer version!), this is not required, as nucleic acids at concentrations as low as 20 ng/mL will precipitate at 0–4°C, so incubation for 15–30 minutes on ice is sufficient.

This step is to wash any residual salt away from the pelleted DNA.

This explanation should bring you up to speed on how ethanol precipitation works. If you want to learn more about the ins and outs of ethanol precipitation and other DNA clean-up approaches, you might want to check these out…

Originally published December 4, 2007. Reviewed and republished March 2021.

Download free EduRev App Saheb hails from Dhaka and he has migrated from Bangladesh in 1971 His house and green fields were destroyed by storm Their poverty

I think Watford is getting a bit of a hard time here Subject to the area, there are definitely nice places to live - Bushey, Cassiobury, Oxhey, Abbots Langley,

Álvar Núñez Cabeza de Vaca was a Spanish explorer of the New World, and one of four survivors of the 1527 Narváez expedition

Does Cat N affect insurance? Yes As we discussed above, if you choose to insure a Cat N car you'll probably find that your insurance premiums will be noticeably higher than they would be for a brand new vehicle

As such, your dog's bean bag will be a place of warmth, cosiness, comfort and most all, security for them , in which they can get all the rest they so desperately need… and that is why your dog loves their bean bag Smaller breeds of dogs such as Chihuahuas or Pomeranian can get away with up to 10 hours sleep per day