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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)
At physiological pH’s (7.0-7.4), both the carboxyl and amino groups are charged
Only L-aminoacids arefound in proteins
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
Resonance forms of peptide bonds.The peptide bond (C) is a hybrid of A and B, giving it a partial double bond character
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
Trans conformation;most common and sterically favored
Cis conformation;found rarely with Pro, sterically unfavorable
The planar nature of the peptidebond restricts the possibleconformations that a proteincan assume. This can be predicted by the angle (aboveor below the peptide bond plane) of the two bondsbetween the -carbon of theconstituent amino acids. These phi () and psi () angles canbe used to predict and define some higher order proteinstructures.
Peptide BondSteric Restrictions