Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20UNIT III:AMINO ACIDS, PROTEINS, & ENZYMESLecture 1: Amino acids, peptides, & proteinsAmino acid metabolism –end of semesterContain amine and carboxylic acid functional groupsEnzymesReceptorsTransportHormonesCarrier proteinsContractile proteinsProtective proteinsWhy study amino acids and peptides?Amino acids are the monomer subunitsused to make proteins – proteins are involved in all functions of living organismsAmino acids and peptides (small chains ofamino acids) are important signaling molecules (neurotransmitters, hormones)Amino acids help buffer the pH in cellsAmino acids are used to synthesizeother vital (non-protein) moleculesAmino acids can be used to provideenergy – very important during fastingH lH2N C COOH l R-CAmino acids have an amine and a carboxylic acid groupGeneric structureof an amino acid H l+H3N C COO- l RGeneric structureof an amino acid@ pH 7amineCarboxylicacid(form doesn’t exist!)pK~2.2(weak acid)R-COOH H+ + R-COO-pK~9.5(base)R-NH3+ H+ + R-NH2Carboxylic acid is a weak acid (proton donor) and amine group isa base (proton acceptor), so both groups can donate/accept a protondepending on the pHHAA-zwitterion14 — 13 — 12 — 11 —10 — 9 —8 —7 —6 —5 —4 — 3 —2 —1 —0 l l l l lpHAdd OH-Add H+pKa = 2.2COOH = COO-+H3N-AA-COOH+H3N-AA-COO-H2N-AA-COO-pKa = 9.5NH3+ = NH2(+1)(-1)(0)chargedbutneutralpIisoelectricpointAmino acids have titration curves thatresemble diprotic or triprotic acids0 1 2 3 4 5 6 7 8 9 10 11 12 13 14pKa = 2.2COOH = COO-pKa = 9.5NH3+ = NH2+H3N-AA-COOH+H3N-AA-COO-H2N-AA-COO-The charge of an amino acid changes with the pHpHpH[H+] = 10-pHpKaHA H+ + A-acid baseIf the pH is below the pKa, the acid (HA) form is mostly present. If the pH is above the pKa, the conjugate base (A-) form is present. You MUST know the acid and conjugate base forms of COOH and NH3+ to make sense of this.Netcharge+10 -1COO- l C NH3+ l CH2 l CH2 l COO-“R”GlutamateH“R” can be any of ~20 different groups of atoms called side chains.Side chains have functional groups that are important in determining protein structure, properties, and function.Four classes of side chains based on chemical/physical properties and types of functional groups they containWhat about the “R” groups? How are amino acids different?All amino acidsare the sameEach amino acidis different-CCOO- l C NH3+ l RHAcidic amino acids – have COOH (or COO-)groups in their side-chains lCH2 lCOOH lCH2 lCH2 lCOOHAsparticacid(Asp)Glutamicacid(Glu)Basic amino acids – have amine groups (NOT amide) groups in their side-chains lCH2 lCH2 lCH2 lCH2 lNH2 lCH2 lCH2 lCH2 lNH lC=NHlNH2 lCH2 lNNHLysine(Lys)Arginine(Arg)Histidine(His)Classes of amino acids based on side chains – acidic & basicCOO- l C NH3+ l RHPolar, neutral amino acids – have amide, alcohol, or sulfhydryl groups in their side-chains lCH2 lOH lH-C-OH l CH3Serine(Ser)Threonine(Thr)Classes of amino acids based on side chains – polar, neutralAsparagine(Asn) lCH2 lC=O lNH2 lCH2 lCH2 lC=O lNH2Glutamine(Gln) lCH2 lSHCysteine(Cys)Tyrosine(Tyr) lCH2 l lOHR1-SH + HS-R2 R1-S-S-R2 + 2H-SH group is a thiol (aka mercaptan) – itis polar, like an alcohol (O & S are similar).2 thiols can be linked to form a “disulfide(S-S) bond – an oxidation.Disulfide bridges are important for protein structureCOO- l C NH3+ l RHNon-polar, neutral amino acids – do not have polaror ionizable groups – in general, their “R” groups arenon-polar (hydrophobic) and hydrocarbon-rich. Classes of amino acids based on side chains – non-polar, neutralGlycine(Gly) lH lCH3Alanine(Ala)Phenylalanine(Phe) lCH2 lValine(Val) lH-C-CH3 l CH3Leucine(Leu) l CH2 l H-C-CH3 l CH3Isoleucine(Ile) l H-C-CH3 l CH2 l CH3Methionine(Met) l CH2 l CH2 l S l CH3Proline(Pro) H lN-COOHdehydration (condensation) RxAmino acids are linked together by amide bondsto form peptides & proteins+ HOHamino-terminalamino acidcarboxy-terminalamino acidPeptide bonds = amide bondsPeptide bonds“N-terminal” “C-terminal”PeptidebondEven with only 3 amino acids, there are 6 different amino acid sequences possible .There are 20 differentamino acids.Most proteins have hundreds of amino acids.The enormous number of unique sequences allows for the enormous variety of protein structure and thus function.20n possible sequencesThe sequence of amino acids in a protein is its “primary structure”and determines its 3-D shape and function NHCHCCH2OHOCOHONHCH CHOH2NCHCCH2OOHNHCHCCH2OCOHOH2NCHCHONHCH CCH2OHOOHNHCH CCH2OOHH2NCHCCH2OCOHONHCHCHOHOHNCHCCH2OCOHONHCHCHOHOH2NCH CCH2OOHH2N CH CHNHOCH CCH2NHOOHCH CCH2OHOCOHOH2NCHCCH2OCOHONHCHCHONHCH CCH2OHOOHH2N-ser-gly-asp-COOHH2N-gly-asp-ser-COOHH2N-asp-ser-gly-COOHH2N-asp-gly-ser-COOHH2N-ser-asp-gly-COOHH2N-gly-ser-asp-COOHGenetic mutations (alterations in DNA) lead to changes in the aminoacid sequence of a protein; altered function associated with this abnormal protein can cause a disease.~ 20,000 genes, but >100,000 proteins in the human bodyProteins and diseaseWhen tissues are damaged (injury or disease), they leak and/or die,releasing their proteins. Levels of tissue-specific proteins in bloodcan be useful in diagnosis/treatments. Differences in amino acid sequence (mutated vs normal) can sometimesbe used to diagnose/detect disease states in patients (if the mutation alters a physical/chemical property of the protein).Some diseases result when pathogens (foreign molecules or toxins)bind to proteins, altering their function.Positively charged proteins move toward the cathode. Negatively charged proteins move toward the anode. Uncharged proteins don’t move at all.Electrophoresis can be used to separate moleculeswith different chargesBuffer chamber@ specific pHBuffer chamber@ specific pHProteinsamplesElectrophoresis strip(sample support)ApplyelectriccurrentHuman serum proteinsseparated be electrophoresisPower supply provides electrical currentAnode (+)Cathode (-)Normal Val-His-Leu-Thr-Pro-Glu-Glu-Lys-Sickle Val-His-Leu-Thr-Pro-Val-Glu-Lys-Hemoglobin A vs Hemoglobin SHuman adult hemoglobin (HbA) consists of2 -chains and