|MadSci Network: Molecular Biology|
Dear Adilesa, I am not fully sure why ethanol has to be ice cold to extract the DNA from onion cells. It seems that the temperature of ethanol depends on the previous temperature of the preparation steps to obtain the DNA. When working with e-coli the incubation stages before adding the ethanol required keeping the cells on ice. Therefore you would want to also add cold ethanol so the temperature in the tube remains the same. Treating the cells with ethanol will dissolve any proteins but does not dissolve the DNA. If you tell me more about your experimentation I might be able to give you a better answer to your question. Sincerely, Michael Watson
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