DNA Extraction

[Alexander Berkow]

Hi, I'm new to this whole listserve thing, but I'm interested to see how it
works.  Here is one question I have been stumped by recently:

Why, in the first round of DNA extractions, do you use phenol (tris-HCl
saturated) and in the second round you use phenol chloroform?  I'm
interested in an answer that explains the chemistry.

One other thing:  Why, when you wash a DNA pellet with 70% ethanol, does the
30% water in the solution not cause the DNA to go back into solution?

Thanks!

Alex