Regulation of EnzymaticActivity and Metabolic PathwaysCopyrightThe McGraw-HillCompanies, Inc.Permission required forreproduction or displayMultienzyme SystemsLinearCyclicABinputcSproductYDE...BranchedDivergentConvergentMN-OPOQV1602R2
16 Regulation of Enzymatic Activity and Metabolic Pathways Multienzyme Systems Linear A B C D E Cyclic U V T input W X Z Y S product Branched O2 O O1 Divergent M N P Q R Convergent M A B C N X Y Z Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display
Direct ControlsontheActionsofEnzymes1. Competitive inhibition - substance thatresembles the normal substrate competeswith the substrate for the active site2. Noncompetitive inhibition - enzymes areregulated by the binding of molecules otherthan the substrate away from the active siteEnzyme repression-inhibits at the geneticlevel by controlling synthesis of key enzymesEnzyme induction- enzymes are made onlywhen suitable substrates are present17
17 Direct Controls on the Actions of Enzymes 1. Competitive inhibition – substance that resembles the normal substrate competes with the substrate for the active site 2. Noncompetitive inhibition – enzymes are regulated by the binding of molecules other than the substrate away from the active site • Enzyme repression – inhibits at the genetic level by controlling synthesis of key enzymes • Enzyme induction – enzymes are made only when suitable substrates are present
FEXRegulationofenzymeactionCopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or displayNoncompetitive InhibitionCompetitive InhibitionSubstrateNormalCompetitivesubstrateinhibitorwithsimilarshapeActivesiteBothmoleculescompeteforthe active siteRegulatorysiteEnzymeRegulatorymolecule(product)EnzymeEnzymeXReactionisblockedReactionproceedsReactionisblockedbecauseReactionproceedsbecausecompetitivebindingofregulatorymoleculeininhibitorisincapableregulatorysitechangesofbecomingaproduct.conformationofactivesitesothatsubstratecannotenter.Product18
Regulation of enzyme action 18 Substrate Reaction proceeds Noncompetitive Inhibition Active site Regulatory molecule (product) Product Regulatory site Reaction is blocked because binding of regulatory molecule in regulatory site changes conformation of active site so that substrate cannot enter . Normal substrate Competitive inhibitor with similar shape Enzyme Enzyme Enzyme Both molecules compete for the active site. Reaction proceeds Reaction is blocked because competitive inhibitor is incapable of becoming a product. Competitive Inhibition Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display
EnzymerepressionCopyright The McGraw-HillCompanies, Inc. Permission required for reproduction or displayDNARNAProteinFoldstoformfunctionalenzyme structureEnzymeSubstrateProductsExcessproductbindstoDNAand shutsdownfurtherenzymeproduction.19DNARNAProteinNo enzyme
Enzyme repression 19 DNA RNA Enzyme Protein Folds to form functional enzyme structure Excess product binds to DNA and shuts down further enzyme production. + Substrate Products 1 2 3 4 7 DNA RNA Protein No enzyme 5 6 Copyright © The McGraw -Hill Companies, Inc. Permission required for reproduction or display
MCFeedback Inhibition of Biochemical PathwaysGrawHH国PlayPauseAudioTextMany of the enzyme-catalyzedreactions that occur in a cell,such as thoseinvolved in thebiosynthesis of an amino acid,are carried out in a specificsequencecalledabiochemicalpathwayCopyrightTheMcGraw-Hill Companies,Inc