chapter 7 Biochemistry

7.1Enzymes7.2Metabolism7.3EnergyTransformation7.4Proteincrystallization–AdditionalReadingChapter7BiochemistryEnzymesallowmanychemicalreactionstooccurwithinthehomeostasisconstraintsofalivingsystem.Enzymesfunctionasorganiccatalysts.Acatalystisachemicalinvolvedin,butnotchangedby,achemicalreaction.Manyenzymesfunctionbyloweringtheactivationenergyofreactions.Bybringingthereactantsclosertogether,chemicalbondsmaybeweakenedandreactionswillproceedfasterthanwithoutthecatalyst.7.1Enzymes•Enzymescanactrapidly,asinthecaseofcarbonicanhydrase(enzymestypicallyendinthe-asesuffix),whichcausesthechemicalstoreact107timesfasterthanwithouttheenzymepresent.Carbonicanhydrasespeedsupthetransferofcarbondioxidefromcellstotheblood.Thereareover2000knownenzymes,eachofwhichisinvolvedwithonespecificchemicalreaction.Enzymesaresubstratespecific.Theenzymepeptidase(whichbreakspeptidebondsinproteins)willnotworkonstarch(whichisbrokendownbyhuman-producedamylaseinthemouth).7.1Enzymes(Continued)ProfessionalWordsandPhrasescatalyst['kætəlist]n.催化剂activationenergy活化能reactant[ri'æktənt]n.反应物chemicalbond化学键carbonic[kɑ:'bɔnik]adj.碳的anhydrase[æn'haidreis]n.脱水酶substrate['sʌbstreit]n.底物peptidase['peptideis]n.肽酶amylase['æməleis]n.淀粉酶•Enzymesareproteins.Thefunctioningoftheenzymeisdeterminedbytheshapeoftheprotein.Thearrangementofmoleculesontheenzymeproducesanareaknownastheactivesitewithinwhichthespecificsubstrate(s)willfit.Itrecognizes,confinesandorientsthesubstrateinaparticulardirection.•Theinducedfithypothesissuggeststhatthebindingofthesubstratetotheenzymealtersthestructureoftheenzyme,placingsomestrainonthesubstrateandfurtherfacilitatingthereaction.Cofactorsarenonproteinsessentialforenzymeactivity.IonssuchasK+andCa2+arecofactors.Coenzymesarenonproteinorganicmoleculesboundtoenzymesneartheactivesite.7.1Enzymes(Continued)•Enzymaticpathwaysformasaresultofthecommonoccurrenceofaseriesofdependentchemicalreactions.Inoneexample,theendproductdependsonthesuccessfulcompletionoffivereactions,eachmediatedbyaspecificenzyme.Theenzymesinaseriescanbelocatedadjacenttoeachother(inanorganelleorinthemembraneofanorganelle),thusspeedingthereactionprocess.Also,intermediateproductstendnottoaccumulate,makingtheprocessmoreefficient.Byremovingintermediates(andbyinferenceendproducts)fromthereactivepathway,equilibrium(thetendencyofreactionstoreversewhenconcentrationsoftheproductsbuilduptoacertainlevel)effectsareminimized,sinceequilibriumisnotattained,andsothereactionswillproceedinthepreferreddirection.7.1Enzymes(Continued)ProfessionalWordsandPhrases(Continued)activesite活性部位inducedfithypothesis诱导契合假说cofactor[kəu'fæktə]n.辅因子coenzyme[kəu'enzaim]n.辅酶intermediate[intə'mi:diət]n.中间产物endproduct终产物NotestotheDifficultSentences•Enzymesallowmanychemicalreactionstooccurwithinthehomeostasisconstraintsofalivingsystem.Enzymesfunctionasorganiccatalysts.Acatalystisachemicalinvolvedin,butnotchangedby,achemicalreaction.Manyenzymesfunctionbyloweringtheactivationenergyofreactions.Bybringingthereactantsclosertogether,chemicalbondsmaybeweakenedandreactionswillproceedfasterthanwithoutthecatalyst.•酶能允许许多化学反应发生在一个生命系统的体内平衡限制体系之内。酶是作为有机催化剂起作用的。催化剂是与化学反应有关、但不改变化学反应的一种化学物质。许多酶是通过降低反应的活化能起作用的。化学键可以通过使反应物相互接近到几乎在一起而被减弱，而且反应本身将比没有催化剂存在的条件下进行得更快。•Metabolismisasetofprocessesperformedbythelivingbeingsthatallowthemtointerchangematterandenergywiththeirenvironment.Thelivingbeingsusethemetabolicprocessestogrowandorganizethemselvesinternally.Thisisoneofthevisiblemanifestationsoflife.Unlikethebiotic(living)systems,someabiotic(inert,withoutlife)systemsgrowexternally;forexample,acopperchloridecrystalgrowstowardoutsideaddingmaterialinitsperipheryorformingnucleiofgrowtharounditself.Thelivingbeingsgrowinternallyalthoughtheydonotreproduce,thatis,eveniftheydonotproducedescendants.Therefore,themetabolismisasetofprocessesusedbythelivingbeingsformaintainingtheirstructureandmolecularorganizationinaquasi-stablestate.7.2Metabolism•Themetabolismconsistsoftwobasictypesofinterdependentphases,thephaseinwhichtheenergyisfreedandthephaseinwhichenergyiscaptured.Thephasethatconsistsofthedisintegrationofcomplexorganiccompoundtoreleaseenergyisknownascatabolism,whereasthephasethatconsistsofthearrangementoforganiccompoundsfromsimplercompoundstostoreenergyiscalledanabolism.7.2Metabolism(Continued)ProfessionalWordsandPhrasesbiotic[bai'ɔtik]adj.生命的,生物的abiotic[eibai'ɔtik]adj.非生物的copperchloride氯化铜crystal['kristəl]n.晶体quasi-stablestate准稳态organiccompound有机化合物catabolism[kə'tæbəlizəm]n.分解代谢anabolism[ə'nabə.lizəm]n.合成代谢•Anexampleofcatabolismisthatacellintakesamoleculeofglucosefromthesurroundingsanddisintegratesittoreleaseenergy(glycolysis).Immediatelyaftertheenergyhasbeenreleased,itiscapturedandstoredbyaspecializedmolecule,theadenosinetriphosphateorATP.WhentheenergythatwasstoredbytheATPisusedinthesynthesisofmorecomplexcompounds(e.g.bondingseveralmonosaccharidestobuildmoleculesofdisaccharidesorpolysaccharides)theprocessisanabolism.7.2Metabolism(Continued)•Generally,thematerialsobtainedduringthecatabolicphasewillbeusedintheanabolicphase.Manymoleculesareusedtoformcel