Amino acid and_protein_chemistery


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  • Peptide bond formation is not spontaneous (favorable in free energy) under normal conditions, and requires conversion of the carboxyl or the amino group to a form which reacts more readily. In general, the carboxylic acid moiety is activated by converting it to an ester, acid chloride, anhydride, azide or some other derivative that makes the carbonyl group more nucleophilic. Note that once you make a peptide bond, the peptide backbone is fairly chemically inert: the nitrogen is no longer as strong a nucleophile, and the linkage is pretty stable and slow to hydrolyze. Proteins are typically digested exhaustively by heating to near boiling temperatures in reasonably strong solutions of hydrochloric acid. As we will learn later, there are of course enzymes that hydrolyze proteins quite efficiently.
  • Amino acid and_protein_chemistery

    1. 1. Proteins are the most abundant and functionally diverse molecules in living systems where they constitute 50% or more of their dry mass.The word protein is derived from the Greek Protos, which means the first or supreme.Proteins are nitrogenous macromolecules,composed of aminoacids linked by peptide bond.
    2. 2. AMINO ACIDSAmino acids are organic solvents.Have two functional groups –NH₂ and -COOH group.The amino group is basic while carboxylic group is acidic in nature.Soluble in water but insoluble in organic solvents e.g chloroform,acetone,ether,etc.All amino acids which make up proteins are L-α- aminoacids.All amino acids have chiral carbon, exept Glycine.
    3. 3. LOW pH NEUTRAL HIGH pH O O OR C R C R C OH O O NH3 NH3 NH2ammonium Form Zwitterion Carboxylate Form
    4. 4. CLASSIFICATION OF AMINO ACIDSAlthough more than 300 naturally occurring amino acids are known but only 20 amino acids take part in the formation of all types of proteins,plants as well as animal in origin.These 20 amino acids are known as Primary,Standard or normal amino acids.
    5. 5. Each of these amino acids has one or more genetic codon(s) which are present within the molecules of specific mRNA which themselves are produced under direction of genes occuring in DNA molecules.
    6. 6. Semi-essential aminoacids. These include Arginine and Histidine.These are growth promoting factors since they are not synthesized in sufficient quantity during growth.
    7. 7. Others includeN-methyllysine,Found in myosinCarboxyglutamate,Found in ProthrombinDesmosine,Found in elastin
    8. 8. Non protein amino acidsThese are the amino acids which donot take part in the protein synthesis, and have no genetic codes.They perform other functions in human metabolism e.g
    9. 9. 6.CitrulineOrnithineArgininosuccinic acidThese three amino acids occur in the liver,where they takepart in the formation of urea.
    10. 10. 7.Pantathenic acid. It is a widely distributed vitamin.It forms a part of the molecule of Co.enzymeA.8.Homocysteine
    11. 11. PEPTIDE BOND
    12. 12. Proteins are made by controlled polymerization of amino acids water is eliminated O Otwo amino acids H2N CH C OH H2N CH C OHcondense to form... R1 R2 N or amino C or carboxy terminus O O terminus...a dipeptide. If H2N CH C NH CH C OH + HOHthere are more itbecomes a polypeptide. R1 R2Short polypeptide chainsare usually called peptideswhile longer ones are called peptide bond is formedproteins. residue 1 residue 2
    13. 13. Classification of peptidesDIPEPTIDESOLIGOPEPTIDES Composed of 3-10 amino acids linked together through peptide bond.e.g Tripeptide(3 amino acids linked together by 2 peptide bonds),Tetrapeptide(4 amino acids linked together by 3 peptide bonds).
    14. 14. PEPTIDESHormonesNeuropeptidesAlkaloidsAntibioticsToxinsRegulatory peptides
    15. 15. 7.Bacitracin,GramicidinThese are antibiotics.
    16. 16. UNUSUAL PEPTIDE BONDIn some cases the peptide bond in a peptide does not involve α-COOH group.e.g Glutathione which has the sequence glutamic acid,cysteine and glycine.However,the –COOH group of glutamic acid forming peptide bond with cysteine is not α but γ.For this reason glutathione is chemically γ-glutamyl- cysteinyl-glycine.
    17. 17. CLASSIFICATION OFPROTEINS ON THE BASIS OF MOLECULAR LENGTH AND SHAPE.Fibrous proteins. When the axial ratio of length:width is more than 10.e.g collagen,α keratin of hair.Globular proteins. When axial ratio of length:width of protein molecule is less than 10.e.g Myoglobin,haemoglobin,ribonucleases.
    18. 18. ON THE BASIS OF SOLUBILITY AND PHYSICAL PROPERTIES.Simple proteinsConjugated proteinsDerived proteins
    19. 19. SIMPLE PROTEINS These are the proteins which on complete hydrolysis yield only amino acids.They are further classified based on their solubilities and heat coagulabilities.1.ALBUMINSoluble in waterPrecipitated by full saturation with ammonium sulfateCoagulated by heatExamples,Ovalbumin.serum albumin,lactalbumin and legumel
    20. 20. 2.GlobulinsInsoluble in water,soluble in dilute salt solutions.Heat coagulablePrecipitated by half saturation with ammonium sulfate.Examples,serum globulins,lactoglobulin,myosin in muscles,ovoglobulin and legumin.
    21. 21. 3.GlobinsRich in histidine but not basic.Combine with heme to form hemoglobin.4.ProlaminsSoluble in ethanol,insoluble in water.Rich in amino acid proline but deficient in lysine.Examples,gliadin of wheat and zein of maize.
    22. 22. 5.Protamines.Basic proteins,soluble in NH4OH.Rich in arginine,lack tyrosine and tryptophan.Form nucleoproteins with nucleic acids.Present in sperm cells.
    23. 23. 6.HistonesStrongly basic proteins as they are rich in arginine.Form nucleoproteinsSoluble in water.Lack tryptophan
    24. 24. 7.AlbuminoidsAlso called scleroproteins,occur only in animals donot occur in plants.Include collagen,keratin and elastin.
    25. 25. COPOUND OR CONGUGATED PROTEINSThese are the proteins which in addition to amino acids contain contain a non protein group called prosthetic group in their structure.1.NucleoproteinsHistones+nucleic acidsMost abundant in tissues having a large proportion of nuclear material e.g yeast,thymus and other glands and sperms.
    26. 26. 2.PhosphoproteinsSimple proteins+phosphoric acidExamples casein of milk and vitellin of egg yolk.3.LipoproteinsSimple proteins+covalently bonded with lipid substances like lecithin,cholesterol,triglycerides and fatty acids.Occur in blood plasma,nervous tissue,egg yolk,milk and cell membrane.Bacterial antigens and viruses also contain lipoproteins.
    27. 27. 3.Carbohydrate containing proteins Proteoglycans,glycoproteins(immunoglobulins,comlement many enzymes).4.Chromoproteins Proteins+coloured pigments HEMOPROTEINS Hemoglobulin Cytochromes catalase Peroxidase OTHERS Flavoproteins Visual purple
    28. 28. 5.MetalloproteinsProteins+metallic atomsExamples,Ferritin(Fe),Carbonic anhydrase(Zn),Ceruloplasmin(Cu).
    29. 29. DERIVED PROTEINSInclude proteins derived from simple and conjugated proteins.1.Primary derived proteinsSynonymus with denatured proteins.Denaturation takes place when some or all of the cross linkages which normally keep the molecular of protein intact are split,although there is no hydrolysis of protein molecule.
    30. 30. Denaturation may be brought about by chemical or physical agents such as heat,X rays,ultrasonic waves,shaking or stirring for long time,extremes of pH,salts of heavy metals,neutral chemical agents such as urea and organic solvents such as alcohol and acetone.In most cases denaturation is irreversible,but in some cases it is reversibleExample,RIBONUCLEASE.(Denaturation is reversible)
    31. 31. Secondary derived proteinsThese substances are intermediates formed in the progresive hydrolysis of protein molecule.They are of different sizes and different amino acid composition.PROTEOSESSoluble in water,coagulated by heat,and are precipitated from their solution by saturation with ammonium sulphate.PEPTONESPOLYPEPTIDESOLIGOPEPTIDES
    32. 32. Classification based on function.Catalytic proteinsRegulatory or hormonal proteinsTransport prpoteinsImmune proteinsContractile proteinsGenetic proteins
    33. 33. Classification of proteins regardingnutritionHIGH QUALITY PROTEINSLOW QUALITY PROTEINS