Amino acidsAmidesPolypeptidesPrimary structureSlide 5Slide 6Secondary structureAlpha helixBeta sheetSlide 10Disulfide bondsProtein functionAmino acidsR-groups non-polarpolaracidicbasicproteins condensation between carboxylic acids and amines ++H2Ocarboxylic acidamineamideCOOHNHCONAmidesamidesresonance structurealanineglycineAla-Gly+H2OdipeptideCONCONCH2NHCOOHCH3CH2NHCOOHHCH2NHCOHCNHCOOHHCH3Polypeptides“backbone”N1-C1-C1-N2-C2-C2-N3-C3-C3-peptide bonds_H_H=OOH_H_H=O=O_R_R_RN-terminal residueC-terminalresiduebiological activity = structureprotein structure 4 levelsPrimary structuresequence of amino acidshemoglobin transports O2 and CO2 4 protein chains 300 amino acids6th amino acid from N-terminusGluVal-CH2CH2-CO2H-CH(CH3)2RSickle cell anemiawater solublewater insolublePrimary structure study evolution-chain 146 residueshorses - humans = 26 pigs - humans = 10 gorillas - humans = 11 successful change /Primary structure -10,000,000 yearsselective hydrolysisPhe-Val-Asn-Gln-HisHis-Leu-Cys-Gly-SerGly-Ser-His-Leu-ValGln-His-Leu-CysHis-Leu-Val-GluLeu-Val-Glu-AlaPhe-Val-Asn-Gln-HisHis-Leu-Cys-Gly-SerGly-Ser-His-Leu-ValGln-His-Leu-CysHis-Leu-Val-GluLeu-Val-Glu-AlaSecondary structurehydrogen bonding backbone groupsH-bond donorsN1-C1-C1-N2-C2-C2-N3-C3-C3-_H_H=OOH_H_H=O=O_R_R_RH-bond acceptorsTwo main secondary structures:-helix-sheetAlpha helixEvery C=O bonded to N-H 4 residues awayforms a helixcore is backboneR-groups outside3.6 amino acids per turnprolinebreaks helix=OCno H-bondingC=ONHBeta sheetEvery C=O bonded to N-H far apart in 1o structureon different chainspeptide chains extended side-by-side maximal H-bonding for anti-parallel chainssmall R-groups above and below the sheetif not  -helix or -sheetrandom coilSecondary structuresome proteins 1o structure amino acid sequence2o structure-helix-sheet-sheet silk-helixcollagen bone, teeth triple heliceskeratin hair, skin, wool, hoovescross-linked with disulfide bondsDisulfide bondscysteine -CH2-SHS-H H-SCHNCCHNCreduced[O]S SCHNCCHNCoxidizedProtein functionenzymes biological catalystsimmunoglobulins antibodiestransport hemoglobinhormones regulationstructural keratin, collagenmotion actin, myocinfunction depends on