Diffusion can occur between the DNA and alcohol? HELP?

During the DNA isolation of a fruit, at the end, the DNA will move into the alcohol layer. Why? Is it because of diffusion? if not, which is the process then?

1 Answer

  • Ted K
    Lv 7
    9 years ago
    Favorite Answer

    Before adding alcohol, the DNA is fully solvated, floating around in solution, so you can't see it. When you add alcohol, the DNA becomes insoluble, and it comes out of solution--i.e. it precipitates (i.e. turns solid). As it comes out of solution, which is pretty much instantaneous, you can now see the DNA fibers swirling around--it's very cool--an example of chremistry that you can actually see wih your own eyes. Stick a stick in there and start twirling, and the DNA fibers will start winding around your stick, just like twirling a fork in spaghetti.

    The way these DNA extractions are done is to first break up the cells or tissue in a salt solution. The salt neutralizes the negative charges on the sugar-phosphate backbone of the DNA. In solution, the positively charged sodium ions from the salt are attracted to, and neutralize the negative charge on the phosphate groups on the DNA. Since the whole complex now has no charge, it is less polar, and therefore a lot less hydrophilic (water-loving), and much less soluble in water.

    What the alcohol does is provide a suitable environment which promotes interaction of the sodium ions with the DNA phosphates (see above), thus effectively shielding the phosphates' negative charge. Alcohol has a lower dielectric constant than water (i.e. it is less polar). This makes it easier for the sodium to grab onto the phosphate. That makes the DNA less hydrophilic and it drops out of solution.

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