Homework Help: Biology

Posted by Christiaan on Tuesday, November 11, 2008 at 6:02am.

In the final step of DNA extraction from E. Coli bacteria, we used ethanol so that the DNA would precipitate.
Why is it that DNA precipitates in ethanol, and not in water? Both of them are polar solvents, and so is DNA. So why doesn't water make DNA precipitate?

Biology - SraJMcGin, Tuesday, November 11, 2008 at 8:45am
Thank you for using the Jiskha Homework Help Forum. Here are some sites on precipitation of DNA:

1. (Wikipedia): http://en.wikipedia.org/wiki/Ethanol_precipitation

2. (the basics): http://bitesizebio.com/2007/12/04/the-basics-how-ethanol-precipitation-of-dna-and-rna-works/

3. (DNA & RNA): http://www.mbi.ufl.edu/~rowland/protocols/ethanol%20precipitation%20of%20dna%20and%20rna.htm

4. (PDF file to download from Vietnam): http://www.mbi.ufl.edu/~rowland/protocols/ethanol%20precipitation%20of%20dna%20and%20rna.htm

Sra

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