Precipitation of Biomolecules - question

[Gato]

Hello all,

 

I was wondering, very generally, what common biomolecules (DNA, RNA, ATP, ADP, inorganic phosphate, etc) precipitate in acid? And what is the basis for this?

 

Thanks!

[Bluenoise]

Ummmm. Well all of them that you listed but inorganic phosphate do.

IT just depends on the PH. If you drop the pH lower than the Pk of an acid it will loose charge and become non-soluable in water (in most cases). The same is true for many bases, you up the pH higher than their pK and they become less soluable.

It just so happens that all those molecules that you listed are acids.

 

For example. DNA is highly water soluable. However dropping the pH to 4.5 will make it non-soluable. This is a good way to seperate RNA from DNA actually. As RNA will stay soluable.

 

You should note that it might not be possible to drop the pH of those molucules low enough to get them to percipitate without them degraded in the process. I'm thinking this is likely the case with RNA.