Amino Acids, Peptides and Proteins
Ferenc Hudecz2013, ELECTROPHORESIS
Objectives: I. Know the general structure of an α amino acid. II. Define the ionic / pH properties of amino acids. A. Conditions where the amino acid is a zwitterion. B. Conditions where the amino acid is at its isoelectric point. 1. How to calculate the isoelectric point of an amino acid given the pKa's of the ionizable groups. C. Conditions where the amino acid is in its cationic form. D. Conditions where the amino acid is in its anionic form. III. Classify a given amino acid as hydrophobic, polar and uncharged, polar with a negative charge (acidic) or polar with a positive charge (basic). A. Subclassifications 1. Aromatic amino acids. a) Properties conferred to proteins by the presence of these amino acids. 2. Sulfur containing amino acids. IV. Amino acids with a chiral carbon (tetrahedral stereocenter) in their structure. A. D / L enantiomeric forms versus R / S enantiomeric forms. V. Describe the structure of the peptide bond. VI. Describe the primary structure of proteins. A. Conditions where peptides and/or proteins are at its isoelectric point. B. Conditions where peptides and/or proteins are in a cationic form. C. Conditions where peptides and/or proteins are in an anionic form. VII. Classification according to size. A. Peptides B. Oligopeptides C. Polypeptides D. Proteins 1. Monomeric Proteins 2. Multimeric Proteins a) Homomultimeric Proteins b) Heteromultimeric Proteins c) Subunits VIII.Be familiar with the convention for drawing the structure and/or writing the amino acid sequence of peptides, oligopeptides, and proteins. IX. Classification of proteins based upon biological function. kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk The α Amino Acids As the name implies, amino acids contain a carboxylic acid group and an amino group. If this was the only criteria for a biologically active amino acid, there would be thousands of possible amino acids. The 20 amino acids found in nature are called alpha (α) amino acids based upon an archaic system of carboxylic acid nomenclature. In this system the carboxyl carbon is carbon 1 and the carbon adjacent to it (carbon 2) is
