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Purifying DNA

Discussion of all aspects of biological molecules, biochemical processes and laboratory procedures in the field.

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Purifying DNA

Postby kikkid » Sun Oct 14, 2007 12:27 am

I have a question and I am not sure if I have the right answer: why it is difficult to purify a specific piece of uncloned DNA using ordinary biochemical techniques? Is it because if you wanted one specific piece from one specific cell it is way too small to expect to get rid of the cell membrane/organelles, etc, and end up with that specific strand of DNA. If you replicate it, you'll end up with millions of copies, only some of which will end up in your resulting sample, and
if you use a number of cells in order to bypass replication, you'd end up with DNA that might not be exactly the same due to mutations or even modifications.
Any insite would be greatly apperciated.
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Postby mith » Sun Oct 14, 2007 2:51 am

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Postby kikkid » Sun Oct 14, 2007 5:31 am

I thought the purpose of this site was to help people learn. If you have no intention of doing so, you should keep your comments to yourself. Some people here are trying to learn. thank you to all those who do assist, as for you others, who think you know so much........many of your so called answers are incorrect. Maybe you should take some time and study the concept of Karma.
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Postby Jammerz » Sun Oct 14, 2007 5:33 am

Somebody gave an answer to the exact same question in that other thread; that's why he posted a link.
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Postby kikkid » Sun Oct 14, 2007 5:41 am

"Very low signal noise ratio, and no good fishing hooks, if I can mix my metaphors... " THIS IS NO ANSWER! I was simply asking if I had the right idea, I am not asking anyone to do my work for me. I am trying to learn, that was just plain disrespectful.
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Postby blcr11 » Sun Oct 14, 2007 7:16 am

Consider the separation principles of “ordinary biochemical methods”. They almost always depend on exploiting some physical or chemical properties that can vary from molecule to molecule. Gel electrophoresis, for example, separates molecules on the basis of size and or charge; sedimentation separates on the basis of density and shape; crystallization separates on the basis of thermodynamic phase properties, and so on. Now consider a sample of DNA. Is there any chemical or physical property (besides sequence) of such a collection of molecules you think you could use as a basis to separate out any specific piece of DNA? All of the molecules will have roughly the same charge. All of them are helical rods. OK, there will be some variation in length and rigidity, but that will get you but a crude separation unless the difference in size is pretty large and distinct; you can separate a plasmid from chromosomal DNA. (Actually, it is possible to separate the individual strands of phage lambda on a CsCl gradient, but that’s a unique case; in general you won’t be able to separate strands that way.) To say “there’s no hook” is only a metaphor for saying that there’s no varying physical of chemical property to use to separate out a specific molecule of DNA. And to say that the signal to noise ratio is too low is essentially saying the same thing—you have no physical or chemical property difference that distinguishes one molecule from another. So, in general, separating out specific pieces of DNA can’t easily be done by classical biochemistry alone. You must also take advantage of the only unique property of a piece of DNA: its sequence; and that most likely means recombinant techniques of one sort or another.
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Postby kikkid » Sun Oct 14, 2007 7:33 am

Thank you for that last post, I really do appreciate it. Being a novice, metaphores in the subject of genetics simply look like a really bad joke, how am I to know?? Thank you very much for taking the time to explain that to me!
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Postby mith » Sun Oct 14, 2007 4:04 pm

It also means that someone from your class is also on here, might be useful to contact them and work together.
Living one day at a time;
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Accepting hardships as the pathway to peace;
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Postby lituus » Mon Oct 15, 2007 4:29 pm

also when you post exactly the same question to yahoo answers a day before it's due, it is pretty darn obvious that you're looking for a freebie

(yahoo answers being the haven for people looking for easy answers to questions asked in fundamental science courses)

you might also consider looking it up in your lecture notes, reading a textbook or using wikiversity/wikibooks

or asking someone for help personally...
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