Hi everybody, I need to encapsulate a plasmid into small vesicles (50-300 nm) so I want to know how can I estimate a plasmid size (like 7 kb) in nanometers, at least his diameter in its supercoiled, relaxed and linear form. I was searching in internet and found persons that says that depends on the composition and DLS can be used for this, but I dont know anyone that use it.
Please if someone can guide me it will be very appreciated. Thanks.
I don't understand your stated size of plasmids. You say '7 kb'. Do you mean a molecular mass of 7 KDa. I can't believe 7 Da as a molecular mass.
On the Malvern Panalytical Zetasizer ZS (which measures diffusion coefficient via DLS) then there's a calculator that will allow you to estimated size based on molecular mass (and vice versa).
Depending on the shape one gets a different estimate of size. See attached. You'll see a radius ~ 2 nm for most structures. That is a diameter of ~ 4 nm.
Alan, by 7kb he means 7000 base pairs of DNA.
Stefano, I can't give you a precise answer because the packing density of DNA would vary somewhat depending upon conditions. You can readily calculate the theoretical volume of a DNA strand of 7kb but that doesn't take into account the repulsion of all the negative charges. A simplistic answer would be to look at the size of bacteriophages, which hold genomes somewhat larger than 7 kb (Lambda for example is a bit less than 50kb) and have capsid sizes around 50nm.
1kb of DNA has a linear length of about 340nm (so 340x7=2400nm), but of course that is in a straight line. Relaxed would be that line in a circle (you can do the math). However those values are fairly useless since the DNA would fold up quite a bit and fill a much smaller volume.
Michael J. Benedik Thank you for the clarification. Molecular mass and size are related so with an estimated molecular mass of the plasmid then a size can be calculated which, of course, will be shape dependent,
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