Regularity of Enzyme ActionCopyright The McGraweHillCeeConstitutive enzymesalways present,alwaysproduced in equalAddmoreamounts or at equalsubstraterates, regardless of theConstitutiveenzymesamount of substrate(a)Regulated enzymes -not constantly present;production is turned onAdd more(induced) or turned offsubstrate(repressed)inresponseEnzymelevelincreasesorto changes in thesubstrate concentrationRemovesubstrateC11EnzymelevelRegulatedisreducedenzymes(b)
11 • Constitutive enzymes – always present, always produced in equal amounts or at equal rates, regardless of the amount of substrate • Regulated enzymes – not constantly present; production is turned on (induced) or turned off (repressed) in response to changes in the substrate concentration Regularity of Enzyme Action (a) Constitutive enzymes or (b) Regulated enzymes Enzyme level increases Add more substrate Add more substrate Remove substrate Enzyme level is reduced Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Synthesis and HydrolysisReactionsCopyright The McGraw-Hill Companies, Inc. Perission required for reproduction ar displaySynthesis orOHcondensation reactionsOHHQPanabolic reactionstoGC2glucoseEnzymemoleculesform covalent bondsATEHCbetweensmallersubstrate molecules.1maltoseEnzymerequire ATP,release onemoleculeOHHmolecule of water forH20each bond formedEnzymeGlycosidicbond(a)CondensationReaction.FormingaglycosidicbondbetweentwoglucosemoleculestogeneratemaltoserequirestheremovalofawatermoleculeandenergyfromATP.12
12 Synthesis and Hydrolysis Reactions • Synthesis or condensation reactions – anabolic reactions to form covalent bonds between smaller substrate molecules, require ATP, release one molecule of water for each bond formed O C C H H OH G G Enzyme (a) Condensation Reaction. Forming a glycosidic bond between two glucose molecules to generate maltose requires the removal of a water molecule and energy from ATP. Glycosidic bond 2 glucose molecules OH HO OH H G G G G O C H H OH H H2O H2O Enzyme 1 maltose molecule Enzyme Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Synthesis and HydrolysisReactionsCopyright @ The McGraw-Hill Comparies, Inc. Permission required for reproduction r displayHydrolysisreactionsNH-O- catabolic reactionsthat break downaaaa2substrates into smallEnzymemolecules; requires theinput of water to breakbondsaataa2EnzymeaaaaEnzymePeptidebond(b)HydrolysisReaction.BreakingapeptidebondbetweentwoaminoacidsrequiresawatermoleculethataddsOHtooneaminoacidandHtotheother.13
13 Synthesis and Hydrolysis Reactions • Hydrolysis reactions – catabolic reactions that break down substrates into small molecules; requires the input of water to break bonds (b) Hydrolysis Reaction. Breaking a peptide bond between two amino acids requires a water molecule that adds OH to one amino acid and H to the other. H2O Peptide bond Enzyme Enzyme aa1 aa1 aa2 aa2 NH C C N H O O OH Enzyme aa1 aa2 C NH O OH H H Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
TheMcGraw-Hill CompaniesConceptCheck:AnenzymeA.becomes part ofthe final productsB.is nonspecific forsubstrateC.is consumed bythereactionD.may be active extracellularlyE.is composed onlyofprotein
Concept Check: An enzyme A. becomes part of the final products B. is nonspecific for substrate C. is consumed by the reaction D. may be active extracellularly E. is composed only of protein
Sensitivity of Enzymes to TheirEnvironment: Activity of an enzyme is influenced by thecell's environment: Enzymes operate under temperature, pHand osmotic pressure of organism's habitat: When enzymes are subjected to changes inorganism's habitat they become unstable- Labile: chemically unstable enzymes- Denaturation: weak bonds that maintainthe shape of the apoenzyme are broken15
Sensitivity of Enzymes to Their Environment • Activity of an enzyme is influenced by the cell’s environment • Enzymes operate under temperature, pH, and osmotic pressure of organism’s habitat • When enzymes are subjected to changes in organism’s habitat they become unstable – Labile: chemically unstable enzymes – Denaturation: weak bonds that maintain the shape of the apoenzyme are broken 15