3 Factors that affect enzyme rates of reaction An enzyme’s rate of reaction is measured by the amount of substrate converted to a product per minute.An enzyme’s activity can be affected by:General environmental factors, such as temperature and pH.Cofactors and coenzymes.Enzyme and substrate concentration which affects the saturation of the active site.Inhibitors.
4 What is the effect of temperature on enzyme function? Optimal temperature fortypical human enzymeenzyme of thermophilic(heat-tolerantbacteria)Temperature (°C)Optimal temperature for two enzymes20406080100Rate of reactionOptimal pH for pepsin(stomach enzyme)Optimal pHfor trypsin(intestinalenzyme)pHOptimal pH for two enzymes12345678910What is the effect of temperature on enzyme function?What is the effect of pH on enzyme function?
5 1. Environmental Factors Each enzyme has an optimal temperature in which it can function.Each enzyme has an optimal pH in which it can function.The wrong temperature of pH can denature an enzyme, which means the enzyme proteins shape is destroyed.
6 2. Cofactors and Coenzymes Cofactors are nonprotein inorganic enzyme helpers.For example, metal ions like iron in hemoglobin hold oxygen.Coenzymes are organic cofactors.For example, vitamins like niacin which serves as an electron acceptor.
7 Example of Cofactor Enzyme Activation: Binding of one oxygen to hemoglobin activates other sites to enhance oxygen binding at the three other sites.7
8 3a. Enzyme Concentration What does the graph tell us about the effect of increasing [enzyme]?Rate of ReactionEnzyme ConcentrationIncreasing the [enzyme] means the rate of reaction keeps increasing.
9 3b. Substrate Concentration What does the graph show us about [substrate]?Increasing [substrate] only increases the reaction rate until all the enzyme active sites are in use.
10 4. Enzyme InhibitorsCompetitive inhibitors bind to the active site of an enzyme, competing with the substrate.Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective.Noncompetitive inhibition is also called allosteric regulation.
11 LE 8-19 A substrate can normally bind to the active site of an enzyme. Normal bindingA competitive Inhibitormimics the substrate,competing for the active site.CompetitiveinhibitorCompetitive inhibitionA noncompetitive inhibitor bindsto the enzyme away from theactive site, altering the shapeof the enzyme so that itsactive site no longer functions.Noncompetitive inhibitorNoncompetitive inhibition
12 AZT and AIDSAZT is the first retroviral drug approved to fight the HIV virus.It is a competitive inhibitor for the enzyme reverse transcriptase.12
13 Allosteric Regulation of Enzymes Allosteric regulation is the term used to describe cases where an enzyme’s function is affected by the binding of a regulatory molecule at a different site than the active site.Allosteric regulation may either inhibit or stimulate an enzyme’s activity.Usually the end product of a long series of reactions that make a metabolic pathway inhibits an enzyme near the beginning of the pathway.This way when the [product] is high the chemical reactions leading to the product are slowed down.
15 Homework Read MHR p 41 – 50 Do p 54 # 1 – 11, 13 Adapt and redraw the diagram on p43 to illustrate an anabolic reaction instead of a catabolic reaction.Note: anabolic = synthesis catabolic = hydrolysis or breakdown
17 Feedback Inhibition Initial substrate (threonine) Active site availableThreoninein active siteEnzyme 1(threoninedeaminase)Isoleucineused up bycellIntermediate AFeedbackinhibitionEnzyme 2Active site ofenzyme 1 can’tbindtheoninepathway offIntermediate BEnzyme 3Intermediate CIsoleucinebinds toallostericsiteEnzyme 4Intermediate DEnzyme 5End product(isoleucine)17
18 Induced Fit Model of Enzyme Action SubstratesEnzymeProductsSubstrates enter active site; enzymechanges shape so its active siteHolds the substrates (induced fit).Substrates held inactive site by weakinteractions, such ashydrogen bonds andionic bonds.Active site acts on substratesSubstrates areconverted intoproducts.Products arereleased.Activesite isavailablefor two newsubstratemolecules.Quick Review ofInduced Fit Model of Enzyme ActionEnzyme-substratecomplex