The number of base pairs should be multiplied by the average molecular mass of one base pair (660 g/mol) to get the approximate mass of the whole double-stranded DNA molecule, such as a plasmid. If the DNA is single-stranded, then multiply the number of bases by the average mass of a single base (330 g/mol) to get the approximate mass of the whole molecule. Better still, if you know the sequence, calculate the exact mass from the sequence.

What did you mean by the "charge ratio?"

well it depends on the type of DNA and the place where it is ... inside a living cell DNA will not exist as single stranded under normal circumstances, so the molecular weight of any DNA from there will be calculated as 660 g/mol, BUT in vitro DNA can exist as ssDNA depending on how denaturing the environment of the solution it is in , or even as ss oligonucleotides(such as PCR primers) ..So in this case if you want to calculate the mol weight of DNA, then  take the avg mol weight as 330g/mol ...

does this answer your question ?

Thanks Manish, but shouldnt we multiply the number of base pairs in the DS-DNA in 660g/mol? Lets assume that plasmid DNA contains 300bp, should we multiply 300bp times the 330g/mol for the ss-DNA?

The number of base pairs should be multiplied by the average molecular mass of one base pair (660 g/mol) to get the approximate mass of the whole double-stranded DNA molecule, such as a plasmid. If the DNA is single-stranded, then multiply the number of bases by the average mass of a single base (330 g/mol) to get the approximate mass of the whole molecule. Better still, if you know the sequence, calculate the exact mass from the sequence.

What did you mean by the "charge ratio?"

Thanks Adam, I am working with Gemini surfactant and DNA charge ratio thats why I am a little bit confused because I am only caring about the quaternary ammonium/ phosphate ratio and DNA is a polymer and we only calculate the unit average molecular weight.

I don't know about this technique, but I'll throw out some ideas. Does it help to consider that since each base has one negative charge and each dimeric cationic detergent molecule has 2 positive charges, there should be, ideally, 1 detergent molecule per two bases in the complex? It seems most likely that the two bases would be next to each other on the same strand of DNA, but that may depend on the structure of the detergent molecule. I would imagine that ionic strength would play a big role in the detergent:DNA stoichiometry by reducing the affinity of the detergent-DNA interaction. Also, there may be steric clashes that would prevent every phosphate from being paired with a detergent charge, lowering the detergent:DNA stoichiometry. Alternatively, I can imagine a structure in which the detergent molecules line up along the DNA in such a way that every phosphate is paired with one charge on a detergent molecule but the other charge is free, leading to a detergent:DNA stoichiometry of 1. It seems like the structure of the complex would depend on the relative amounts of detergent and DNA in the mixture.

You have the precise answer to your second question by Adam

Hi Aula,

you can follow this link to calculate/convert wight to molarity according to your sample DNA nucleotide numbers.

http://www.molbiol.edu.ru/eng/scripts/01_07.html

Hi, yes, that's correct. However, there is a common mistake with the molecular weight of a base pair. A mass of two water molecules must be subtracted from the value if the base pair is part of a DNA molecule. To obtain correct values, you can use the following online calculator:

http://www.molbiotools.com/dnacalculator.html

Hello, i want to know how we can calculate N/P ration of Polyamidoamine G5 (Molecular weight 28,824 and free surface amino group 128) and the plasmid DNA one base pair has 660g/mol molecular weight.  kindly guide.

Dear imran ,you should first know the molecular weight of PAMAM monomer then put those value in formula of N/P ratio.

n/p= amt of polymer/avg mol wt of polymer monomer divided by amt of pDNA/

avg mol wt of pDNA