MCHowEnzymes WorkirawHH自品0PlayPauseAudioTextEnzymesare proteins that speed up chemical reactions in the cellCopyrightTheMcGraw-Hill Companies,Inc
FEXApoenzymes:SpecificityandtheActive SiteExhibits primary, secondary, tertiary, and some,quaternary structureSite for substrate binding is active site, or catalytic siteCopyright The McGraw-Hll Companies, Inc. Permission required for reproduction or display.Levels of StructurePrimarySecondaryTertiaryWAs the poly peptide(a)forms intrachain bondsandfolds,itassumesathree-dimensional0(tertiary)state thatdisplays an active siteaS(b) Because eachdiff erent poly peptidefolds differently,each-#-apoenzymewill haveadifferently shaped activesiteQuatemaryAS(c) More complexenzymeshaveaquatenarystructureconsisting ofmore than一one poly peptide. Theactivesimay beformed bythejunction oftwo poly peptides.AS
7 Apoenzymes: Specificity and the Active Site • Exhibits primary, secondary, tertiary, and some, quaternary structure • Site for substrate binding is active site, or catalytic site AS AS Levels of Structure AS AS Primary Secondary Tertiary Quaternary (a) As the poly peptide f orms intrachain bonds and f olds, it assumes a three-dimensional (tertiary ) state that display s an activ e site (AS). (b) Because each dif f erent poly peptide f olds dif f erently, each apoenzy me will hav e a dif f erently shaped activ e site. (c) More complex enzy mes hav e a quaternary structure consisting of more than one poly peptide. The activ e sites may be f ormed by the junction of two poly peptides. Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display
FEXApoenzymes:SpecificityandtheActiveSiteAtemporaryenzyme-substrate unionoccurswhensubstratemoves into active site -induced fitAppropriate reaction occurs; product is formed and releasedCopyright The McGraw -HillCompanies, Inc. Permission required for reproduction or displaySubstrate (S)Products?EScomplexEnzyme(E)Doesnotfit(b)(a)(c)8(d)
8 Apoenzymes: Specificity and the Active Site • A temporary enzyme-substrate union occurs when substrate moves into active site – induced fit • Appropriate reaction occurs; product is formed and released (a) (b) (c) (d) Substrate (S) Products S Does not fit E E E Enzyme (E) ES complex E Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display
Cofactors:SupportingtheWorkofEnzymesCopyright The McGraw -HillCompanies, Inc. Permis sion required for reproduction or display.Chemicalgroup(Ch)Substrate2(S2)Substrate1(S)1.AnenzymeMicronutrientswithacoenzymepositionedtoreactwith twosubstrates.are needed asCoenzymeEnzyme(C)complex(E)cofactors2.Coenzymepicksupachemicalgroupfromsubstrate1Cofactors actas carriers to3.Coenzymeassist thereadiesthechemicalgroupfortransfertoenzyme in itssubstrate2.hactivity4.Final actionisforgrouptobeboundtosubstrate2;alteredsubstrates9arereleasedfromenzyme
9 Cofactors: Supporting the Work of Enzymes • Micronutrients are needed as cofactors • Cofactors act as carriers to assist the enzyme in its activity 1. An enzyme with a coenzyme positioned to react with two substrates. 2. Coenzyme picks up a chemical group from substrate 1. 4. Final action is for group to be bound to substrate 2; altered substrates are released from enzyme. 3. Coenzyme readies the chemical group for transfer to substrate 2. Substrate 2 (S2 ) Coenzyme (C) Chemical group (Ch) Substrate 1 (S1) Enzyme complex (E) S2 S1 C E Ch C E S1 S1 C E Ch Ch Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display. S2 S1
Location of Enzyme ActionExoenzymes -transported extracellularly,where theybreak down large food molecules or harmful chemicals-Cellulase,amylase,penicillinaseEndoenzymes - retained intracellularly and function there- Most enzymes are endoenzymesCopyright The McGraw-Hil Companies, nc. Permission required for reproduction or displaySubstrateProductsActiveProductsenzymeEnzymeInactiveSSubstrateenzymes10EndoenzymesExoenzymes(a)(b)
10 Location of Enzyme Action • Exoenzymes – transported extracellularly, where they break down large food molecules or harmful chemicals – Cellulase, amylase, penicillinase • Endoenzymes – retained intracellularly and function there – Most enzymes are endoenzymes (a) (b) Exoenzymes Endoenzymes Active enzyme Substrate Products Enzyme Substrate Products Inactive enzymes Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display