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. BOND PEPTIDE

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 C  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  -carbon of the constituent amino acids. These phi (  ) and psi (  ) angles can be used to predict and define some higher order protein structures. Peptide Bond Steric Restrictions

23. Levels of Protein Structure