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. 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 Ca atom

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

22. Peptide Bond Steric Restrictions 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 a-carbon of the constituent amino acids. These phi (f) and psi (y) angles can be used to predict and define some higher order protein structures.

23. Levels of Protein Structure