In this class, we treat all ionizing groups with in a molecule, as acting independently of other ionizing groups. The pH on the titration curve where an AA has no net charge is called the pI or isoelectric point. Continue doing this until all the protons have been removed. Some of you have trouble figuring out which group ionizes first. Carboxylic acids give up their protons at acid pHs.
Amines give up their protons at basic or alkaline pHs.
Amino groups near a carboxylic acid have a more acidic pK than isolated amines. Asp, Glu, Lys, and Arg. Their pK values and structures are shown below.