Metabolism part 2 Proteins part 3 Enzyme Catalyzed Reactions 1 General rule creating complexity increases entropy Is spontaneous Needs no net energy Usually still require catalysts Biological processes chemical reactions that require energy hydrolysis Respiration General rule reducing complexity Biological processes chemical reactions that reduce complexity Learning goal Students should be able to explain how explain how cells control the rate of chemical reactions metabolism and drive energetically unfavorable biochemical reactions Focus how enzymes catalyze reactions by decreasing EA and coupling ATP hydrolysis to endergonic reactions 4 Enzymes reduce eliminate the energy of activation barrier What is energy of activation How do enzymes reduce it Enzymes cannot change the free energy difference between reactants and products 5 G the difference in free energy between the reactants and products A BC AB C 6 Activation energy required to reach transition unstable state Exergonic Endergonic This spontaneous reaction can now occurs spontaneously in a cell This nonspontaneous reaction still requires additional energy 7 Enzymes reduce eliminate the need for activation energy Enzyme catalyzed reactions Exergonic Endergonic 8 General principle of biology Stable lower energy states Equilibrium Systems at euqilibrium 9 General principle of biology Unstable unequal states are high energy states They take more energy to create and maintain and they can be used to do cellular work 10 Activation energy is a function of chance encounters 1 how often reactants collide heat kinetic energy concentration 1 2 2 In what orientation reactants collide 3 The instability of the transition state 4 energy needed to strain and break bonds Factors like pH salinity and temp that affect shape of organic molecules 1 cells keep these constant 11 General rule 2 Enzymes decrease Ea not G Enzymes decrease Ea because 1 They bring reactants into close proximity 2 They hold reactants in exactly the right conformation 3 They hold reactants in a way that strains the chemical bonds 12 General rule 3 Enzyme structure is critical for function Active site s Where substrates bind Binding Interactions between molecules and enzyme R groups Highly dependent on enzyme shape Affinity how strongly a substrate is attracted to an active site relative to other molecules 13 General rule 3 Enzyme structure is critical for function Enzymes are flexible dynamic they change shape conformation when substrates or inhibitors bind to them 14 General rule 4 A cell drives nonspontaneous reactions by coupling them to spontaneous reactions G Energy released R G P P R Reaction 1 Reaction 2 Spontaneous Nonspontaneous Reaction 1 is almost always the 15 ATP hydrolysis exergonic Negative charges compressed together General rule 4 A cell drives nonspontaneous reactions by coupling them to spontaneous reactions Pi Pi ATP G ADP P Pi i R G P ADP R Reaction 1 Modified reaction 2 Spontaneous Now Spontaneous A phosphate group increases the of the reactants This is called 17 General rule 4 A cell drives nonspontaneous reactions by coupling them to spontaneous reactions Reactant B is chemically modified A B A B endergonic Figure 9 3 18 Enzymes are PROTEINS enzymes proteins function structure ALTER THESE primary structure 2 3 4 structure monomers polymerization ionic covalent nonpolar H bond interactions 19 General rule 4 Enzymes are OPTIMIZED for biological conditions rate 10 C 100 C 20 At an enzyme s OPTIMIZED biological range the rate of the reaction depends on concentration of substrates reactants at some point you will reach saturation of enzyme concentration of the enzyme structure of enzyme presence of cofactors coenzymes prosthetic groups regulatory modifications that alter structure phosphorylation inhibitors 21 For recitation consider this problem You have three different versions of an enzyme that catalyzes a particular reaction B differs from A by one amino acid in the primary sequence a K to F switch C is identical to A except it s missing five amino acids off the N terminus Explain the results you see below enzyme A rate of reaction enzyme B enzyme C 0 1M 1M 2M 3M increasing concentrations of substrate reactants present 22 For the exam You should be able to use examples to explain how proteins support cell function and discuss the importance of enzymes in living systems You should be able to describe the structure and function of enzymes and how they can catalyze both exergonic and endergonic reactions you should be able to explain how enzymes reduce activation energy of chemical reactions but why they cannot change the overall G You should be able to connect enzymes to everything you learned about proteins in chapter 3 their structure their polymerization and how they fold into a 3D shape and the consequences of disrupting folding with pH or temperature 23 For the exam You should be able to relate what you learned about chemical reactions to explain how cells can perform nonspontaneous chemical reactions in cellular conditions and why this doesn t break the laws of thermodynamics coupling an endergonic to an exergonic reaction via the hydrolysis of ATP how enzyme reduce activation energy You should be able to predict whether and how and why changing the following variables might change the rate of an enzyme catalyzed reaction concentration of the reactants concentration of the enzyme mutation of the enzyme in a noncritical spot mutation of the enzyme in an active site addition of a competitive inhibitor increase concentration of enzyme or reactants addition of a noncompetitive inhibitor increase concentration of enzyme or reactants temperature pH salinity 24