What role do each of the three solvents have during the DNA extraction?
a) phenol
b) chloroform
c) isoamyl alchol

Dear marmite-ga;

Thank you for allowing me an opportunity to answer your interesting
question.

In simple terms (as your question price suggests) these ingredients
are used for extraction and (primarily) for purification purposes.

In spite of some of the comments below, while agreeably dangerous if
handled improperly, these solvents are commonly used for this purpose.
One must assume that if you know how to extract DNA, you are probably
trained to use caution so as not to kill yourself in the process.
Having said that, let's move on to the answer, shall we?

There are a number of ways to extract DNA but for simplicity sake I’ll
assume you are talking about the most common and uneventful method. In
this instance, the purpose of the phenol is to denature proteins in
the sample. When completed, the phenol that can be visibly identified
is then removed in a later step. Eventually, at the final extraction,
a prescribed ratio of chloroform and isoamyl alcohol is added to the
specimen, which is then placed in a micro centrifuge. The ensuing
vortex and the combination of ingredients removes traces of any
potentially contaminating phenol used in the earlier process that
could not be visibly detected and physically removed as the residual
elements clings to the suspended aqueous layer, leaving behind the
desired byproduct; pure, unadulterated DNA.

In short, all three ingredients are used to some degree to purify the
DNA sample, either from inherent impurities themselves (natural or
otherwise) or from other solvents used in the extraction process.

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Best regards;
Tutuzdad-ga


INFORMATION SOURCES

GENERAL LABORATORY METHODS
http://www.research.umbc.edu/~jwolf/method2.htm

SEQUENCING TIPS
http://www.umanitoba.ca/institutes/manitoba_institute_cell_biology/Sequence/Sequence_miniprep.htm


SEARCH STRATEGY


SEARCH ENGINE USED:

Google ://www.google.com


SEARCH TERMS USED:

PHENOL DNA

ISOAMYL ALCOHOL DNA

Very helpful. Especially with the search strategy hints and the prompt reply.
Thanx

For a start, I wouldn't use this technique.  Phenol is too toxic. 
There are much safer alternatives.

Phenol will destroy all lipid structures, membranes and the like,
liberating the DNA into the medium.

Chloroform is a solvent for DNA

Isoamyl alcohol is an anti-foaming agent

xarqi

*phenol denatures proteins; chloroform denatures proteins and
stabilizes the organic/aqueous boundary; isoamyl alcohol aids in the
separation of the two phases and decreases the foaming
    *

*phenol must be ultra-pure ( oxidation products of phenol can damage
nucleic acids) The pH must also be >7.8 or DNA will partition into the
organic phase (ie. you will be dumping it into the waste container!)

Me - I like the guanidine-HCl/chloroform version - sure, we can handle
phenol OK, by why even bother taking a minor risk and having the
hassles of disposal if there is a perfectly acceptable alternative.