1. Faculty of Chemistry, VUT Brno, 2 nd March 2006 Presentation about Amino acids by František SURMAN

2.   Description – general properties Amino acids are derivatives of carboxylic acids formed by substitution of  -hydrogen for amino functional group.Amino acids are derivatives of carboxylic acids formed by substitution of  -hydrogen for amino functional group.

3. majority of amino acids has amphoteric character – functional group –COOH is the reason of acidity and –NH 2 group causes basic properties.majority of amino acids has amphoteric character – functional group –COOH is the reason of acidity and –NH 2 group causes basic properties. in basic environment AA dissociate proton to form carboxyl anion –COO -. Basic surround defends –NH 2 against dissociation.in basic environment AA dissociate proton to form carboxyl anion –COO -. Basic surround defends –NH 2 against dissociation. in acidic environment AA accept proton to form amonium cation –NH 3 +. Acidic environment defends –COOH against dissociation.in acidic environment AA accept proton to form amonium cation –NH 3 +. Acidic environment defends –COOH against dissociation.

4. Zwitterionic structure is neutral and its value of pH is called isoelectric point.Zwitterionic structure is neutral and its value of pH is called isoelectric point.

5. AA are optically active molecules and asymmetry of their mirror images is not superimposable (except in the case of glycine where the R-group is hydrogen)AA are optically active molecules and asymmetry of their mirror images is not superimposable (except in the case of glycine where the R-group is hydrogen) according new UIPAC nomenclature L- D- forms were replaced for (S)- and (R)- system according new UIPAC nomenclature L- D- forms were replaced for (S)- and (R)- system

6. Ordinary synthesis of asymmetric molecules produces racemic mixtures. To obtain the naturally ocurring (S-) AA we must revolve the racemic form. Fortunately we know a variety of ways.Ordinary synthesis of asymmetric molecules produces racemic mixtures. To obtain the naturally ocurring (S-) AA we must revolve the racemic form. Fortunately we know a variety of ways. Biosynthesis of substances of AA having asymmetric centers almost produce pure stereoisomers. Using this criteria, examination of amino acids in practice always shows racemic mixture.Biosynthesis of substances of AA having asymmetric centers almost produce pure stereoisomers. Using this criteria, examination of amino acids in practice always shows racemic mixture.

7. Physical propeties – AA are colourless crystalline substances soluble in water and insoluble in organic solvents with high melting point.Physical propeties – AA are colourless crystalline substances soluble in water and insoluble in organic solvents with high melting point. ValineArginine AlanineLysine

8. Position of amino group −  -amino acids exist in two enantiomeric forms. Only L-(S-) acids are found in nature.Position of amino group −  -amino acids exist in two enantiomeric forms. Only L-(S-) acids are found in nature. Proteinaceous AA − proteins consist of 20 AA.Proteinaceous AA − proteins consist of 20 AA. Essential (unexpendable) − organism is not able to synthesize these AA but accept from food.Essential (unexpendable) − organism is not able to synthesize these AA but accept from food. Nonessential (expendable) − organism produced from essential AA by transamination.Nonessential (expendable) − organism produced from essential AA by transamination. According R- functional groupAccording R- functional group Nonpolar (hydrophobic)Nonpolar (hydrophobic) Polar (hydrophilic) – better soluble in waterPolar (hydrophilic) – better soluble in water Basic – contains more atoms of nitrogenBasic – contains more atoms of nitrogen Acidic – contains more carboxylesAcidic – contains more carboxyles   Separation of amino acids

9.   Summary of 20 proteinaceous AA Essential AA ValinValin LeucinLeucin IsoleucineIsoleucine ThreonineThreonine LysinLysin MethioninMethionin PhenylalaninePhenylalanine TryptophanTryptophan ArginineArginine HistidineHistidine

10. Nonessential AA AlanineAlanine AsparagineAsparagine AspartateAspartate CysteineCysteine GlutamateGlutamate GlutamineGlutamine GlycineGlycine ProlineProline SerineSerine TyrosineTyrosine

11. Besides basic 20 proteinaceous AA more AA exist found only in some organisms. Essential AA are different for variety of animal species and plants are able to synthesize all 20 AA.

12. Polymerization – form peptides, proteins and enzymes A condensation reaction between the carboxyl of one amino acid and the amino group of another forms a peptide bond.A condensation reaction between the carboxyl of one amino acid and the amino group of another forms a peptide bond. PeptidesPeptides Oligopeptides − condensation of 2 – 10 AA unitsOligopeptides − condensation of 2 – 10 AA units Polypeptides − condensation of 11 – 100 AA unitsPolypeptides − condensation of 11 – 100 AA units Proteins − more than 100 AA unitsProteins − more than 100 AA units   Reactions of amino acids

13. Disulfide linkage – conversion of cysteine to cystine is like a conversion of thiols to disulfides by mild oxidizing agents. This conversion can be reversed by mild reducing agents.Disulfide linkage – conversion of cysteine to cystine is like a conversion of thiols to disulfides by mild oxidizing agents. This conversion can be reversed by mild reducing agents. Disulfide bonds stabilize protein structure by providing cross-link.Disulfide bonds stabilize protein structure by providing cross-link.

14. A variety of methods have been developedA variety of methods have been developed Important in industry due to the commercial relevanceImportant in industry due to the commercial relevance  bodybuilding supplements (for big musles)  sources of vitamins not only for human also for animals   Synthesis of  -amino acids

15.  The Gabriel synthesis (from potassium phthalimide)  The Strecker synthesis  Enantioselective synthesis produces only or predominantly pure AA form. (More info Solomons & Fryhle p.1175 - 1177)

16.   Metabolism of  -amino acids

17. THANK YOU FOR ATTENTION