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Amino acids
- 1. AMINO ACIDS Dr KshemaThakur, PhD Molecular Biology & Biochemistry
- 2. General structure ofamino acids Monoamino monocarboxylic acids Or α-amino α-carboxylic acids
- 3. The 20 KeyAmino Acids • More than 300 amino acids occur naturally, but 20 of them are especially important. • These 20 amino acids are the building blocks of proteins, the most abundant biological macromolecules.
- 4. FUNCTIONS OF PROTEINS Enzymes Hormones Contractileproteins Antibodies Transport protein Tissue proteins Feather Spider web Hair/nails Mushroom poisons Lens protein of the eye Milk proteins Light producing molecule in firefly Serve as source of energy during starvation Molecular instruments for expression of genetic information Etc. . .
- 5. L- and D-Stereoisomers of amino acids (L-isomers exist mainly in human system)
- 6. Amino acid Threeletter code One letter code Alanine Ala A Arginine Arg R Asparagine Asn N Aspartic acid Asp D Cysteine Cys C Glutamine Gln Q Glutamic acid Glu E` Glycine Gly G Histidine His H Isoleucine Ile I Amino acid Three letter code One letter code Leucine Leu L Lysine Lys K Methionine Met M Phenylalanine Phe F Proline Pro P Serine Ser S Threonine Thr T Tryptophan Try W Tyrosine Tyr Y Valine Val V
- 7. CLASSIFICATION 1. Based onside chain Nonpolar Polar Aromatic 2. Based on nutritional requirement Essential Nonessential Semiessential 3. Based on metabolic fate Ketogenic Glucogenic Mixed ketogenic and glucogenic
- 8. Gly is theonly amino acid which is achiral Pro is actually an imino acid (with amino group at secondary position) and destabilizes α-helices Met is methyl donor for biological reactions
- 9. Ser and Thrform sites for phosphorylation at –OH Cys forms disulphide bridges
- 10. Formation of Cystineand disulphide bridges
- 11. Arg has Guanidiniumgroup His has Imidazole ring
- 12. Trp has indolering Aromatic amino acids give proteins their characteristic absorption at 280 nm
- 13. BASED ON NUTRITIONAL REQUIREMENT EssentialSemi-essential Non-essential Isoleucine Arginine Glycine Leucine Histidine Alanine Threonine Serine Lysine Cysteine Methionine Aspartate Phenylalanine Asparagine Tryptophan Glutamate Valine Glutamine Tyrosine Proline
- 14. BASED ON METABOLICFATE 1. Glucogenic Ala, Arg, Asn, Asp, Cys, Gln, Glu, Gly, His, Meth, Pro, Ser, Thr, Val 2. Ketogenic Lys, Leu 3. Mixed ketogenic and glucogenic Ile, Phe, Tyr, Trp
- 15. MNEMONICS Polar side chain: Santa’sTeam Crafts New Quilts Yearly Ser, Thr, Cys, Asn, Gln, Tyr Non polar side chains: Grandma Always Visits London In May For Winston’s Party Gly, Ala, Val, Leu, Ile, Met, Phe, Trp, Pro Electrically charged: Dragons Eat Knights Riding Horses Asp, Glu, Lys, Arg, His Essential amino acids: Any Help In Learning These Little Molecules Proves Truly Valuable Arg, His, Ile, Leu, Thr, Lys, Met, Phe, Trp, Val
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- 17. NON-α-AMINO ACIDS β-Alanine β-Aminoisobutyric acid γ-Aminobutyricacid (GABA) δ-Aminolevulinic acid (ALA) Taurine
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- 19. pI: isoelectric pH(equal amount of postive and negative charge) Amino acids in solution: Ampholytes Acid (proton acceptor) Base (proton donor) Diprotic in nature
- 20. TITRATION OF AMINOACIDS pI = pKa1 + pKa2 2 pI = 5.97
- 21. Properties of aminoacids 1.Reactions due to carboxylic group 2.Reactions due to amino group 3.Reactions due to side chain
- 22. The amino acidswill undergo alpha decarboxylation to form the corresponding “amines”. Thus biologically important amines are produced from amino acids. Histidine → Histamine + CO2 Tyrosine →Tyramine + CO2 Tryptophan →Tryptamine + CO2 Lysine →Cadaverine + CO2 Glutamic acid → Gamma Amino Butyric Acid (GABA) + CO2 DECARBOXYLATION 1. Reactions due to carboxylic group
- 23. The carboxyl groupof amino acids can release a H+ ion with the formation of Carboxylate (COO–) ions. These may be neutralized by cations like Na+ and Ca+2 to form Salts. Thus amino acids react with alkalies to form “Salts”. 1. Reactions due to carboxylic group Reaction with Alkalies (Salt formation)
- 24. Amino acid reactswith Amines to form “Amides”. 1. Reactions due to carboxylic group REACTION WITH AMINES Aspartic acid – Asparagine Glutamate - Glutamine
- 25. When the aminoacids are treated with acids (like HCl), it forms “Acid Salts”. 2. Reactions with –NH2 group Reaction with Acids (Salt formation)
- 26. Ninhydrin reagent reactswith free amino group of amino acid yielding purple colored product. Ninhydrin can react with imino acids as proline and hydroxy proline but gives yellow color. Reaction with Ninhydrin 2. Reactions with –NH2 group
- 27. 1- Millon reaction:for phenolic group of tyrosine gives red colored mass 2- Rosenheim reaction: for trptophan and gives violet ring. 3- Pauly reaction: for imidazole ring of histidine: gives yellow to reddish product 4- Sakaguchi test: for guanido group of arginine and gives red color. 5- Lead sulfide test (sulfur test): for sulfur containing amino acids as cysteine give black color precipitates. 3. Reactions due to side chain (R)
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