I want to do some rheology on DNA at theta condition. But I do not know how to achieve the theta condition for DNA solutions. Under different NaCl concentrations, I am thinking to use static light scattering to calculate the second viral coefficient. By doing so, I think I can figure out the ionic strength under which A2 goes to zero. But I also have some questions on the theta condition of DNA solutions.
1. I suppose the theta condition figured out for a short DNA will also apply for longer chains, right?
2. I suppose different isoforms (i.e., linear, relaxed circular and supercoiled) of DNA have different theta conditions, am I right?
3. Besides static light scattering, is there another better way to do this?
It may be tangent to your question, but this article may be an interesting reference for you if you're not already aware:
http://dx.doi.org/10.1021/ma801382j
Yes, it does not deal with your question directly, but you may want to consider the effects discussed in the paper if you are looking to do rheology on DNA solutions.
While not being a biochemist, I’d throw in my two cents anyway.
I would think temperature would be a factor. The molecular weight does influence onset of phase separation (the observed phenomenon). In the limit of infinitely high molecular weight, the cloud point and theta temperature are the same, whereas they diverge at lower Mw (cloud point being higher than theta temp which is a direct consequence of the translational entropy). I would think conformational structures would influence this as the number of sites available for hydrogen bonding would depend on this as well.
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