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Unformatted text preview: B iochemis ry E duca ion Department of iochemistry & Molecular iology University of New Mexico BIOC 423 Int oducto y Biochemist y How Enzymes Catalyze Reactions Reaction Thermodynamics OBJECTIVES • Be able to predict the spontaneity of a chemical reaction from the free energy change. • Define the relationship between standard free energy and the equilibrium constant. • Understand the differences between Δ G, Δ G o and, Δ G o ’. • Describe the common features of the active sites of enzymes. • Describe how enzymes accelerate the rate of reactions. • Compare and contrast thermodynamics in closed and open systems. Define steady state. • Be able to calculate Δ G ’ for coupled reactions given the standard free energies OUTLINE Catalysts Differences between enzymes and other catalysts Measuring enzyme activity Reaction thermodynamics Reaction progression Gibbs Equation Steady state reactions or open systems How enzymes function Catalytic mechanisms Naming enzymes Coupled Reactions LECTURE Catalysts Chemistry and biochemistry are sciences that study the process of change. This change can be on the scale of an organism moving from one location to another or it can be as small as the rotation about a single bond in molecule. Both of these dramatically different processes involve chemical reactions in which the change process is dependent upon the reaction rate of individual or hundreds of reactions. Obviously living systems demand that chemical reactions will proceed at a rate sufficient to support life. Not all reactions, left unaided can proceed at that rate. As we learned in our general chemistry courses, the rate at which a reaction take place can be increased dramatically by the addition of a catalyst. Typically, the catalysts discussed in general and organic chemistry are acids, bases or metal surfaces. In biochemistry catalysts are also necessary to insure a sufficient reaction rate, only in the case of biochemistry the catalysts are usually protein molecules called enzymes . Enzymes differ from other catalysts in one very important respect – they are exquisitely specific for the reactant. From your general chemistry courses recall that for a reaction to be spontaneous it must be exergonic (produce heat during the course of the reaction).However, just because a reaction may be exergonic does not mean that the reaction will happen spontaneously. There also needs to be a pathway that allows the reaction to proceed. In many of the reactions with which you are familiar this pathway required an acid or a base catalyst as part of the “pathway”. This is a second function of catalysts. An example of this point is the hydrolysis of an ester into a carboxylic acid and an alcohol....
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