1 Enzymes

Why Are Enzymes So Important? Why are we devoting one whole lecture topic to a protein molecule? – All chemical reactions in living organisms require enzymes to work Image: Jumping rope, Meagan E. KleinJumping rope From the Virtual Cell Biology Classroom on ScienceProfOnline.comVirtual Cell Biology ClassroomScienceProfOnline.com

Chemical Reactions A process that changes one set of chemicals to another set of chemicals Reactants – elements or compounds that enter into a chemical reaction Products – elements or compounds produced by a chemical reaction

Chemical Reactions 2H 2 + O 2 → 2H 2 O reactants products Involves the breaking of bonds in the reactants and the formation of new bonds in the product Chemical equations – the symbols and numbers used to represent each element or substance in a chemical reaction

Energy in Reactions – Energy Changes Chemical reactions that release energy often occur spontaneously. –Ex. 2H 2 + O 2 → 2H 2 O Chemical reactions that absorb energy will not occur without a source of energy. –Ex. When water is changed into hydrogen and oxygen gas

Energy in Reactions – Activation Energy Activation energy – energy needed to get a reaction started

7 What Are Enzymes? ProteinsMost enzymes are Proteins CatalystAct as Catalyst to accelerate a reaction Not permanentlyNot permanently changed in the process Make materials needed by the cell

Catalyst A substance that speeds up the rate of a chemical reaction by lowering the reaction’s activation energy

9Enzymes catalyzeAre specific for what they will catalyze aseEnd in –ase-Sucrase-Lactase-Maltase

10 How do enzymes Work? weakening bonds which lowers activation energy Enzymes work by weakening bonds which lowers activation energy

11Enzymes Free Energy Progress of the reaction Reactants Products Free energy of activation Without Enzyme With Enzyme

12 Enzyme-Substrate Complex substance enzyme substrate The substance (reactant) an enzyme acts on is the substrate Enzyme Substrate Joins

13 Active Site active site enzyme bindssubstrateA active site of an enzyme molecule binds to the substrate. Enzyme Substrate Active Site

14 enzyme substrate product active site Enzymes are not changed by the reaction, they are reusable

Active site of the enzyme Two substrates Enzyme

The active site is like a lock The substrates fit like a key in a lock Enzyme

The activation energy for these substrates to bind together has been lowered by the enzyme. Enzyme Chemical reaction!!!

Basic Enzyme Diagram Active site The substrates have reacted and changed into the product Enzyme is unchanged

Lock & Key model Fit between the substrate and the active site of the enzyme is exact Like a key fits into a lock very precisely The key is analogous to the enzyme and the substrate analogous to the lock.

21 Induced Fit shapeA change in the shape of an enzyme’s active site InducedInduced by the substrate

Induced Fit Model Enzymes can form to the shape of its substrate. Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College

23 What Affects Enzyme Activity? Three factors:Three factors: Temperature pH Inhibitors

24 Temperature -Effects rates of enzyme activity -Hot temps increase activity -Low temps reduce acitivity - High temps denature (unfold) enzyme. - High temps may denature (unfold) the enzyme.

pH Effect on rates of enzyme activity –Changes in pH changes protein shape~ Denatures –Most human enzymes = pH 6-8 depends on where in body pepsin (stomach) = pH 3 trypsin (small intestines) = pH 8

26 Two examples of Enzyme Inhibitors a. Competitive inhibitors: resemble enzyme’s normal substrate competeactive site a. Competitive inhibitors: are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site. Enzyme Competitive inhibitor Substrate

27Inhibitors b.Noncompetitive inhibitors: do not enter the active sitebind to another part enzymeenzyme change its shape alters the active site Inhibitors that do not enter the active site, but bind to another part of the enzyme causing the enzyme to change its shape, which in turn alters the active site. Enzyme active site altered Noncompetitive Inhibitor Substrate

For Catalase Lab EX for lab: Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as vegetables, fruit or animals). It catalyzes the decomposition of hydrogen peroxide to water and oxygen.

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