Amino acids contain, withing the same molecule, an acidic and a basic function group. Therefore, they can internally donate a proton and exist either as a neutral or charge separated species.

Proteins, polymers of amino acids, can be charged. Not only can the end groups be charged, but some side groups also behave like acids and bases and can be charged. When an amino acid is placed in a buffered solution, it may have a net charge. This is illustrated for alanine [local]. At the isoelectric point of a protein, the protein has no net charge.

Explore the titration behavior of amino acids.