Protocol Online logo
Top : New Forum Archives (2009-): : Molecular Biology

Is DNA an acid because of phosphate group - (Mar/09/2010 )

why is DNA or RNA are acids for having phosphate group. Is it like negatively charged are acids?


Yes it is the same like other acids. The base is hydrophobic which dosent have any charge, the sugar is hydrophilic and it is only the phosphate groups that give it a over all a net negative charge.

If you need further calrification, please give a mail at



Hi snemani1177, welcome to the BioForums!

As you know, DNA is composed of a double-stranded string of nucleotides (A, T, C, and G), each contributing a deoxyribose sugar, a phosphate ion, and a nitrogenous base. When assembled, the exposed face of a DNA molecule is composed of alternating phosphates, which are proton donors at neutral pH (thus, at neutral pH, they're negatively charged, or acidic). The basic portion of each nucleotide is tied up inside the helix, and thus does not react with the environment, thus the overall charge of the molecule is negative, or acidic.

We can see this in electrophoresis (the DNA migrates towards the positive pole), and in how we precipitate DNA -- by using excess positively-charged ions (e.g. sodium) to quench the negative charges and create a DNA salt.