In this chapter, students will be able to understand: Properties of amino acids, basic amino acid structure, amino acid enantiomers, amino acid classification, aliphatic (alkane) amino acids, aromatic amino acids, sulfur containing amino acids, acidic amino acids, polar uncharged amino acids. | Chapter 3 Amino acids, peptides, and proteins Properties of Amino Acids capacity to polymerize novel acid-base properties varied structure and chemical functionality chirality Basic Amino Acid Structure a-carbon is chiral (except for glycine) at pH uncharged amino acids are zwitterions amino acids have a tetrahedral structure side chain carboxyl group amino group a-carbon Amino Acid Enantiomers Steroisomers / enantiomers Biological system only synthesize and use L-amino-acids Amino Acid Classification Aliphatic Aromatic Sulfur containing Polar/uncharged basic/acidic Hydrophobic Hydrophillic Aliphatic (alkane) Amino Acids Proline (pro, P)- cyclic “imino acid” Glycine(gly, G)-only non-chiral amino acid, not hydrophobic Alanine (ala, A) – R-group = methyl-group Valine (Val, V) –Think V! Leucine (Leu, L) – Isoleucine (Ile, I) -2 chiral carbons Hydrophobicity Aromatic Amino Acids All very hydrophobic All contain aromatic group Absorb UV at 280 nm Phenylalanine (Phe, F) Tyrosine (Tyr, . | Chapter 3 Amino acids, peptides, and proteins Properties of Amino Acids capacity to polymerize novel acid-base properties varied structure and chemical functionality chirality Basic Amino Acid Structure a-carbon is chiral (except for glycine) at pH uncharged amino acids are zwitterions amino acids have a tetrahedral structure side chain carboxyl group amino group a-carbon Amino Acid Enantiomers Steroisomers / enantiomers Biological system only synthesize and use L-amino-acids Amino Acid Classification Aliphatic Aromatic Sulfur containing Polar/uncharged basic/acidic Hydrophobic Hydrophillic Aliphatic (alkane) Amino Acids Proline (pro, P)- cyclic “imino acid” Glycine(gly, G)-only non-chiral amino acid, not hydrophobic Alanine (ala, A) – R-group = methyl-group Valine (Val, V) –Think V! Leucine (Leu, L) – Isoleucine (Ile, I) -2 chiral carbons Hydrophobicity Aromatic Amino Acids All very hydrophobic All contain aromatic group Absorb UV at 280 nm Phenylalanine (Phe, F) Tyrosine (Tyr, Y) – -OH ionizable (pKa = ), H-Bonding Tryptophan (Trp, W) – bicyclic indole ring, H-Bonding Sulfur Containing Amino Acids Methionine (Met, M) – “start” amino acid, very hydrophobic Cysteine (Cys, C) – sulfur in form of sulfhydroyl, important in disulfide linkages, weak acid, can form hydrogen bonds. Contain carboxyl groups (weaker acids than a-carboxyl-group) Negatively charged at physiological pH, present as conjugate bases (therefore –ate not –ic acids) Carboxyl groups function as nucleophiles in some enzymatic reactions Aspartate – Glutamate – Acidic Amino Acids Basic Amino Acids Hydrophillic nitrogenous bases Positively charged at physiological pH Histidine – imidazole ring protonated/ionized, only amino acid that functions as buffer in physiol range. Lysine - diamino acid, protonated at pH Arginine - guianidinium ion always protonated, most basic amino acid Polar side groups, hydrophillic in nature, can form hydrogen bonds Hydroxyls of Ser and Thr weakly ionizable Serine .
