|MadSci Network: Molecular Biology|
Dear teacher, I should begin by telling you that DNA is said to be highly stable. There is no difference between samples of DNA. All DNA molecules are the same and the only difference of storage will be triggered by solvant (buffer) in which the DNA is dissolved. I believe that you can readily store DNA at 4 degrees Celsius for a long time without fearing any degradation. As a buffer, I would suggest a TE solution (10 mM Tris.HCl-1mM EDTA, pH 7.5). In molecular biology, the integrity of DNA is often essential. And here, we could mean many things for the word 'integrity'. First of all, you should know that DNA molecules have their biological properties from their sequences and/or structures (secondary and tertiary). So, in your case, you should try to find out in what aspect you are interested. Assuming that you're only interested in the chemical stability (no bother with secondary or tertiary structure), I would suggest an electrophoresis method (that is an agarose or acrylamide gel). The goal is to denature the DNA so that the migration on the gel will be strictly based on the length (charge) of the DNA. If all your DNA molecules have the same length, you should see one band on your gel. If your DNA is degraded, you should see a 'smear'. However, you have to take care that your gel is really in denaturing conditions so that the smear is not a population of different conformations of DNA. However, if you are working with plasmids (like 99.5% DNA scientists do !), you will always get about three bands on an agarose gel. This is because there is always a population of plasmids that have a nick (a break) in the backbone somewhere. This is not a bad sign for your DNA. It's just normal. Anyway, as I said in the beginning, there should be no real problem in storing your DNA at 4 degrees Celsius. Hope this helps, Sincerely, Daniel.
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