CTAB is used in DNA extraction to simultaneously solubilize plant cell walls and membranes while denaturing proteins. This prevents DNA degradation during isolation and yields highly intact genomic DNA. Chloroform helps separate proteins and polysaccharides from nucleic acids by binding them, allowing DNA to be isolated in the upper aqueous phase. Isopropanol precipitates DNA from large solution volumes at room temperature to avoid coprecipitating other molecules. Chilled ethanol causes DNA to precipitate out of solution, allowing it to be purified for genetic testing. Deionized water is used to dissolve and store extracted DNA for subsequent experiments.

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Role of chemicals used in DNA extraction
1. CTAB
CTAB was established sometime ago as the best detergent to use during the extraction/isolation
of highly polymerized DNA from plant material. This detergent simultaneously solubilizes the
plant cell wall and lipid membranes of internal organelles and denatures proteins (enzymes).
Thus, the DNA is not hydrolyzed during the isolation process and as long as vortexing or
vigorous shaking are avoided highly polymerized (i.e., very high intact) genomic DNA is
obtained. First, CTAB is a powerful cationic surfactant. It disrupts membranes and releases
DNA. Second, plant tissues are rich in complex polysaccharides and secondary metabolites like
polyphenols etc. These metabolites interfere and co-precipitate with DNA during the isolation
procedure. CTAB along with some other chemical like Polyvinylpyrrolidone (PVP) is used to
minimize the effect of these metabolites.
2. Chloroform
It solubilizes lipids and a lot of proteins to remove them from the DNA. Chloroform is used to
help separate proteins and polysaccharides from nucleic acids in the cell. The purpose of the
Chloroform will be to help bind up the complexed proteins and polysaccharides. Chloroform is
denser than water solutions and thus after spinning this solution Chloroform and water will
separate into two distinct phases. The lower phase will be Chloroform. This is the phase that
proteins and polysaccharides find most chemically attractive. The upper aqueous phase will
contain your DNA. With plant tissue there is often more polysaccharides than in animal tissue. If
the polysaccharides are not removed many procedures such as restriction enzyme digests will not
work appropriately

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3. Chilled Isopropanol
DNA is less soluble in solutions containing isopropanol than in solutions containing ethanol. In
contrast to precipitation with ethanol, which requires 23 volumes of alcohol, precipitation with
isopropanol is performed with 0.60.7 volume of alcohol. Isopropanol is often the better choice
when precipitating DNA from large volumes of solution. Precipitation with isopropanol is
performed at room temperature to lessen the risk that solutes like sucrose or sodium chloride will
be coprecipitated with the DNA. Isopropanol use useful for precipitations where you have a large
sample volume.
4. Chilled Ethanol
DNA does NOT dissolve in ethanol. That, in fact, Chilled Ethanol used. It precipitates the DNA -
causes it to come out of solution. Cold alcohol is used to separate DNA out of water-based
solutions. This allows the DNA to be purified for subsequent genetic testing. Adding alcohol to a
solution containing DNA is a simple way to obtain the pure DNA required, and colder
temperatures slow down enzymes that can break down DNA, giving better extraction results.
5. Deionized water
DNA get dissolve in water so we can keep it store in water to use DNA for the next experiments
it is deionized you get rid of ions which can interfere with the extraction.
References:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3323937/
http://csmbio.csm.jmu.edu/bioweb/Bio480/Fall05/Tuesday1/dnalink.htm
http://www.researchgate.net/post/What_is_the_role_of_salt_isopropanol_and_ethanol_in_DNA_extraction
http://www.molecularcloning.com/index.php?prt=5
https://in.answers.yahoo.com/question/index?qid=20110704135752AAq48Li
http://www.ehow.com/about_6399349_cold-alcohol-used-dna-tests_.html

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