I have been trying to work this out over 2 days now and I just don't understand! The side chains of Aspartic acid and Glutamic acid both have the reactive group COO-. I don't understand how the COO- is an acidic group! To me, I can see how it could be a basic group - the H+ binds to the COO- and becomes COOH. But how does COO- donate a H+ ion??? And the same question for the basic amino acid side chains. How is NH3+ a basic group? Doesn't NH3+ become NH2 in solution and therefore donates a H+??