Is DNA an acid because of phosphate group
Posted 09 March 2010 - 05:48 PM
Posted 30 May 2010 - 12:04 AM
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Posted 30 May 2010 - 03:04 AM
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.