Fundamentals of Biochemistry Third Edition Donald Voet • Judith G. Voet • Charlotte W. Pratt Chapter 4 Amino Acids Copyright © 2008 by John Wiley & Sons, Inc. Section 1 – Amino Acid Structure zwitterions Titration of Glycine pI – isoelectic point of an amino acid or protein. The pH at which a protein or amino acid has no net charge. Formation of Peptide bond H2 O A W D G Two representations of an amino acid at neutral pH (a) Structure (b) Ball-and stick model Stereochemistry • Stereoisomers - compounds that have the same molecular formula but differ in the arrangement of atoms in space • Enantiomers - nonsuperimposable mirror images • Chiral carbons - have four different groups attached • RS – nomenclature is not used for amino acids • LD – nomenclature used for amino acids L=levo: rotates polarized light to the left D=dextro: rotates polarized light to the right Section 3 – Amino Acid Derivatives Aequorea victoria Practice: Questions: 1, 3 – 12, 15 – 17