DNA precipiatation

Mike McShan wmcshan at REX.RE.UOKHSC.EDU
Wed Jan 24 18:33:22 EST 1996

>In article <4e53v3$pne at mserv1.dl.ac.uk>,
>Joe Bateman <Joseph.Bateman at ucl.ac.uk> wrote:
>>Dear everyone,
>>                I am a molecular biology first year PHd student and
>>therefore carry out procedures such as bacterial minipreps on a day to day
>>basis. One thing which has been puzzling me is the chemical interaction
>>between the alcohol, for example ethanol or isopropanol, and DNA which
>>causes the DNA to precipitate and come out of solution. I am aware that the
>>addition of sodium acetate allows the sodium salt of DNA to form enabling
>>its aggregation but am unsure of the chemistry behind the actual DNA
>>precipitation. If anyone could shed any light on this subject I would be
>>interested to hear from them.

I would recommend that you consult Wolfram Saenger's excellent book,
"Principles of Nucleic Acid Structure" (Springer-Verlag, 1984).   Saenger
discusses the condensed forms of DNA on pages 432 and 433.  In the presence
of Mg(II), polyamines, basic polypeptides or alcohols, DNA in solution
adopts condensed forms displaying a variety of interesting and
macroscopically visible (by EM) morphologies:  beaded fibers, straight
rods, and even toroids.  These macroscopically dense structures are easily
harvested from solution by centrifugation.  The interaction of the poly
anionic DNA with these various charged species is the driving force behind
the condensations.

Hope this information is helpful.

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