Calculating net charge

[babbagee]

How would I go about calculating the net charge of a base such as guanine at a ph of 3.5. The pka of guanine is 2.4.

Thanks

[GCT]

well at a pH of 2.4 half of guanine would be in its non-protonated form (for the relevant acid motif) and half unchanged. With a higher pH there would be more of the basic conformation. One way is to use the henderson hasselbach equation, taking into account the different acid/sites pertinent to guanine.

That is if it has, for instance, two relevant Kas, then there are various ways. If you're in biochemistry, I'm sure that they will teach you simpler methods, I think one way is to determine the isoelectric point and relate from there.