Amino acids: ionic forms with pH, isoelectric point and peptide bonds

ChemistryBiomolecules & PolymersAges 17–18

In ion mode, drag the pH slider from 0 to 14 and watch the amino acid's structure change instantly — a cation in acid, a zwitterion near the isoelectric point, an anion in base; the fraction bar and the average charge are computed from real pKa values, and the molecule migrates toward the cathode or anode in an electric field, staying still exactly at its pI. In peptide mode, choose the number of residues and press Run to watch the amino acids link up through –CO–NH– bonds, each one releasing a water molecule.