Biomolecules: Amino Acids and Peptides

Lecture 4, Medical Biochemistry

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

Non-protein Amino Acids

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

Post-translational Modifications

BOND PEPTIDE

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

Levels of Protein Structure