Lecture 4: Medical Biochemistry, Biomolecules: Amino Acids and Peptides

1. Biomolecules: Amino Acids and
Peptides
Lecture 4, Medical Biochemistry

2. Lecture 4 Outline
• Present and discuss the properties of amino
acids
• Discuss the importance of pKa values and
amino acid titration curves
• NOTE: Ignore the techniques section in
your book chapter 4 (p. 33-34)

3. At physiological pH’s (7.0-7.4), both
the carboxyl and amino groups are
charged
Only L-amino
acids are
found in
proteins

12. Non-protein Amino Acids

13. Examples of Clinical
Aminoacidurias
• Metabolic defects: Phenylketonuria (Phe),
Tyrosinemias (Phe,Tyr), Maple Syrup Urine
Disease (Leu, Val, Ile), Alcaptonuria (Tyr)
• Absorption/transport defects: cystinuria (Cys),
Hartnup disease , Fanconi’s Syndrome
• These diseases are generally diagnosed from
indicators in the urine or plasma. These diseases
will be discussed further in the amino acid
metabolism lectures

14. Post-translational Modifications

18. BONDPEPTIDE

19. Resonance forms of peptide bonds.
The peptide bond (C) is a hybrid of A and B,
giving it a partial double bond character

20. Planar nature of the peptide bond. The
partial double bond characteristic prevents
free rotation around the C-N bond; keeping it
in the same plane with the attached O and H
atoms. These planar bonds can pivot around
the shared Cα atom

21. Trans conformation;
most common and
sterically favored
Cis conformation;
found rarely with Pro,
sterically unfavorable

22. The planar nature of the peptide
bond restricts the possible
conformations that a protein
can assume. This can be
predicted by the angle (above
or below the peptide bond
plane) of the two bonds
between the α-carbon of the
constituent amino acids. These
phi (φ) and psi (ψ) angles can
be used to predict and define
some higher order protein
structures.
Peptide Bond
Steric Restrictions

23. Levels of Protein Structure