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dna has negative charge?

Postby phale » Thu Dec 06, 2007 7:19 pm

I did the DNA extraction experiment this afternoon. I used strawberry, broccoli, pea and apple as my sources and strawberry turned out to be the richest DNA resource. However, what I wonder is that why DNA goes to rubbing alcohol. Is it because DNA is negative charged? If so, rubbing alcohol must be positive charged? Could you please explain more?
Thank you!

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Postby staryl13 » Thu Dec 06, 2007 7:34 pm

This website should clear things up a bit... ... teria.html
Hope it helps, good luck with the project!
"There is a single light of science, and to brighten it anywhere is to brighten it everywhere." -Isaac Asimov

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Postby Willz » Fri Dec 07, 2007 9:53 pm

Ah, the DNA extraction experiment!
To get to the point, yes, DNA is negatively charged; however, this does not necessarily mean that rubbing alcohol is positively charged. In fact, the precipitation of DNA is due to the fact that DNA is insoluble (does not dissolve) in alcohol; all other components of the mixture stay in solution. Although DNA is insoluble in alcohol, DNA is soluble in water. More information can be obtained here: ... ine99.html

Hope this helps!

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Postby Craig_Bridge » Sat Dec 08, 2007 12:30 pm

Willz wrote:DNA is negatively charged;
when it is in an acqueous solution because it ionizes and gives up a hydrogen.

There are a couple of fine points to DNA (and other intracellular protien) extraction methods related to solubility. Water and alcohol are "miscous" (they intermingle). Most procedures call for puring cold >90% alcohol through the acqueous lysing solution containing DNA and caution to never shake or stir. The goal is for the thermal properties of the cold alcohol mixture to cause it to go to the bottom and the thermal sensitive solubility of DNA in alcohol to precipitate it and drag the DNA down with it into an acqueous / alcohol mixing zone from which you can hook it and pull it out and put it somewhere else for further use.

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