1Enzymes 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.7Enzymes 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. 89101112131415161718Reducing activation energy increases the rate of a biochemical reaction by increasing the probability that this free energy barrier is climbed. 192021 It is crucial to understand the Gibbs free energy (including entropy) of the sequential steps of enzyme catalysis.222324252627282930313234353638This 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. 39This 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. 40For 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. 414243The 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. 444546This NAD(P) coenzymes will be used in many reactions we will study later. Understanding them now will bear much fruit in the near future. 47Remember that curved arrow diagrams are always about electrons (when properly drawn). 484950Keep 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. 515253545557585960Notice 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. 6162Notice 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.