Fundamentals of Biochemistry

Fourth Edition

Chapter 4Amino Acids

Copyright © 2013 by John Wiley & Sons, Inc. All rights reserved.

Donald Voet • Judith G. Voet • Charlotte W. Pratt

Chapter 4Amino Acid Structure

Key Concepts 4.1• The 20 standard amino acids share a common structure but differ in their side chains.• Peptide bonds link amino acid residues in a polypeptide.• Some amino acid side chains contain ionizable groups whose pK values may vary.

General Structure of α-Amino Acid

Structures of Standard Amino Acids

Structures of Standard Amino Acids

Structures of Standard Amino Acids

Structures of Standard Amino Acids

Dipolar Amino Acid: Zwitterion

Condensation of Two Amino Acids

Nonpolar Side Chains

Uncharged Polar Side Chains

Cysteine Can Form Disulfide Bonds

Charged Polar Side Chains

AlanyltyrosylaspartylglycineAla-Tyr-Asp-Gly

AYDG

Amino Acid Nomenclature

Chapter 4Amino Acid Structure

Checkpoint 4.1 • Draw a generic amino acid and identify the carbon and its substituents.• Draw the structures of the 20 standard amino acids and give their one- and three-letter abbreviations.• Draw a Cys–Gly–Asn tripeptide. Identify the peptide bond and the N- and C-termini, and determine the peptide’s net charge at neutral pH.• Classify the 20 standard amino acids by polarity, structure, type of functional group, and acid–base properties.• Why do the pK values of ionizable groups differ between free amino acids and amino acid residues in polypeptides?

Chapter 4Stereochemistry

Key Concepts 4.2 • Amino acids and many other biological compounds are chiral molecules whose configurations can be depicted by Fischer projections.• The amino acids in proteins all have the L stereochemical configuration.

Modified Amino Acids in Proteins

Biologically Active Amino Acid Derivatives

Dimerization of Glutathione