1 Enzymes are proteins polypeptides Enzymes need to be in a precise conformation or shape in order to perform enzymatic catalysis This concept will be important to understanding catalysis and when enzymes are put into different settings and situations 7 Enzymes only lower the activation energy of a biochemical reaction They don t change the free energy of a reaction Activation energy is a parameter that limits the rate of a reaction representing a free energy barrier that must be climbed for the reaction to proceed 8 9 10 11 12 13 14 15 16 17 18 Reducing activation energy increases the rate of a biochemical reaction by increasing the probability that this free energy barrier is climbed 19 20 It is crucial to understand the Gibbs free energy including entropy of the sequential steps of enzyme catalysis 21 22 23 24 25 26 27 28 29 30 31 32 34 35 36 38 This image and the next illustrate the three contact points rule for an enzyme to produce a chiral center from a non chiral but prochiral substrate Take time to think this through carefully 39 This image and the preceding illustrate the three contact points rule for an enzyme to produce a chiral center from a non chiral but prochiral substrate Take time to think this through carefully 40 For those who are unfamiliar with the term oxidoreductases this is the same as redox enzymes catalyzing coupled oxidation and reduction reactions Keep in mind these are general GROUPS of enzymes and that actual individual enzymes are very specific for a particular biochemical reaction and substrate 41 42 43 The listed items are the kinds of physical processes enzymes have evolved to make use of Some of them have the effects of lowering activation energies and others of increasing the effective local concentrations of reactants Watch carefully for examples of these specific molecular strategies in the individual enzymes we will study later 44 45 46 This NAD P coenzymes will be used in many reactions we will study later Understanding them now will bear much fruit in the near future 47 Remember that curved arrow diagrams are always about electrons when properly drawn 48 49 50 Keep in mind that biochemistry is a field involving an overlap of many areas of chemistry biochemical systems have evolved to use The thermodynamics of enzymes can often involve organic chemistry of acid base catalysis for example 51 52 53 54 55 57 58 59 60 Notice the spatially precise arrangement of the enzyme and its substrate made possible by the highly evolved amino acid sequence and thus tertiary structure of this enzyme including both its substrate binding and catalytic amino acid residues 61 62 Notice the mirror image roles in acid base catalysis these two histidines will play in the following steps We will see analogous phenomena in later enzymes we study Various amino acid side chains can act as either a base or an acid depending on their local chemical microenvironment and the effective local pH 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80