扬州大学：《生物化学 Biochemistry》课程教学课件（讲稿）03 Amino acids, peptides, and proteins

Amino acids, peptides.and proteins

Amino acids, peptides, and proteins

KeyPrinciplesIn every living organism, proteins are constructed from a commonsetof20aminoacidsIn proteins,aminoacidsarejoined in characteristiclinearsequencesthrougha commonamidelinkage,the peptidebond.aemaid] For study, individual proteins can be separated from the thousandsofother proteins present ina cell, based ondifferences intheirchemical and functional properties arising from their distinctaminoacid sequences.Shapedby evolution,aminoacid sequences areakeyresourceforunderstanding the function of individual proteins and for tracingbroader functional and evolutional relationships

Key Principles  In every living organism, proteins are constructed from a common set of 20 amino acids.  In proteins, amino acids are joined in characteristic linear sequences through a common amide linkage, the peptide bond.  For study, individual proteins can be separated from the thousands of other proteins present in a cell, based on differences in their chemical and functional properties arising from their distinct amino acid sequences.  Shaped by evolution, amino acid sequences are a key resource for understanding the function of individual proteins and for tracing broader functional and evolutional relationships. [ˈæmaɪd] 酰胺

ProteinsElementsComponents of life.Carbon.HydrogenMacromoleculesProteins(polypeptides).Oxygen-NucleioacidsWater.NitrogenCarbohydrates(polysaccharides)-sometimes SulfurlonsandLipidssmall molecules

Proteins Elements •Carbon •Hydrogen •Oxygen •Nitrogen •sometimes Sulfur Components of life

ProteinsMost structurallyand functionally diversegroupofbio-moleculesFunction(involvedinalmosteverything)enzymes(pepsin,polymerase,etc.)酶['keratn]["kplad3an]structure (keratin, collagen)结构carriers&transport(membranechannels)转运receptors&binding(defence:antibodies)受体contraction(actin&myosin)收缩signalling(hormones:insulin)信号storage (bean seed proteins)储存

Proteins Most structurally and functionally diverse group of bio-molecules  Function (involved in almost everything )  enzymes (pepsin, polymerase, etc.)酶  structure (keratin, collagen)结构  carriers & transport (membrane channels)转运  receptors & binding (defence: antibodies) 受体  contraction (actin & myosin)收缩  signalling (hormones: insulin)信号  storage (bean seed proteins)储存 [ˈkerətɪn] [ˈkɒlədʒən]

Most areglobularProtein structure variesPolypeptides smallPolypeptideInsulin (pig)DNApolymerase(E.coliKlenowfragment)Releasedfromthepancreastosignal the[sinersaiz] Synthesizesa newDNAchain usingan existingavailabilityof the metabolicfuel glucoseDNAstrandasatemplateProteinPolypeptidesComplexof3peptidesmaltoser'molteuz]麦芽糖Maltoporin (E.coli)Permits sugars to cross themaltoporinr'moiteparn)麦芽糖孔蛋白bacterialcellmembrane

Protein structure varies Most are globular Polypeptide DNA polymerase (E. coli Klenow fragment) Synthesizes a new DNA chain using an existing DNA strand as a template Polypeptides small Insulin (pig) Released from the pancreas to signal the availability of the metabolic fuel glucose Protein ≠ Polypeptides Maltoporin (E.coli) Protein ≠ Polypeptides Maltoporin (E.coli) Permits sugars to cross the bacterial cell membrane Complex of 3 peptides [ˈsɪnθɪˌsaɪz] maltose [ˈmɔːltəʊz]麦芽糖 maltoporin [‘mɔːltəpərɪn]麦芽糖孔蛋白

AreviewofisomersIsomers-Samechemicalformula,differentpropertiesStructural -Stereoisomers['speifal]DifferentbondsSame bonds,different spatialarrangementDiasteriomers-Enantiomerscis vstransmirrorimagesarrangements

 [ˈspeɪʃəl ]

AminoAcidsShareCommon StructuralFeatureseea carbon and fourCOOsubstituentsαcarbonisthechiralcenter+HH.NtetrahedralRDifferentsidechain-

 Different side chain→

Amino Acid Substituentsfoursubstituents:rerea- a carboxyl groupCOO- an amino group-- a hydrogen atom- an Rgroup (aside6dchain unique to eachHNHaamino acid)o. glycine has asecond hydrogenRatominsteadofanRgroup

TheAminoAcidResiduesinProteins areLStereoisomers.two possiblestereoisomers=H.Nenantiomers(a)D-AlanineL-AlanineopticallyactiveCOOCOOinteract with light differentlyH3N-C-HNHH-DsystemspecifiesCHeCHa(b)L-AlanineD-AlanineabsoluteconfigurationCOO-COO-HaNNH3HMirrorimageofeachother-CH3CH(c)L-AlanineD-Alanine

Mirror image of each other → interact with light differently

Aminoacid chiralityCHOCHOChiral carbon:HOH,CICH20Hbound to 4HOOHdifferent groupsD-GlyceraldehydeL-GlyceraldehydeExcept?[.glisa'raelda,haid]甘油醛COO-COO.MirrorimagesR..IR+H3NNH3+AHD-Amino acidL-Amino acid[livao'raotatan]L=levorotatory,rotatepolarizedlighttotheleftD=dextrorotatory,rotatepolarized lighttotherightAll aminoacidsfound inproteinsareL-enantiomersStereochemistryinaminoacidsplaysroleinoverallproteinstructure

Amino acid chirality L = levorotatory; rotate polarized light to the left D = dextrorotatory; rotate polarized light to the right All amino acids found in proteins are L-enantiomers Stereochemistry in amino acids plays role in overall protein structure [ˌɡlɪsəˈrældəˌhaɪd]甘油醛 [ˌliːvəʊ'rəʊtətərɪ]