CEnzymes - Enzymes Metabolism Enzyme characteristics...

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Enzymes & Metabolism Heyer 1 Enzymes and Metabolic Pathways Enzyme characteristics Made of protein Catalysts : – reactions occur 1,000,000 times faster with enzymes – Not part of reaction • Not changed or affected by reaction • Used over and over Why do cells need enzymes? Not enough time to leave things to chance Most probable reactions are not the required Important molecules do not always occur in large quantities But since life processes are dependent upon enzymes, organisms cannot survive at high temperature – Heat denatures proteins Mechanism of Enzyme Action Ability of enzymes to lower activation energy due to structure. Each type of enzyme has has a highly-ordered, characteristic 3-dimensional shape (conformation). – Ridges, grooves, and pockets lined with specific amino acids. – Pockets active in catalyzing a reaction are called the active sites of the enzyme. Mechanism of Enzyme Action (continued) Substrates have specific shapes to fit into the active sites (lock- and-key model): Substrate fits into active sites in enzyme. Perfect fit may be induced: Enzyme undergoes structural change. Enzyme-substrate complex formed, then dissociates. Products formed and enzyme is unaltered. Reactants must collide for reaction to occur
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Enzymes & Metabolism Heyer 2 Without enzymes, collisions are random An enzyme brings reactants together by binding to them Induced Fit Model 1. Enzyme binds substrate, forms complex 2. Substrates orient for productive collision Induced Fit Model 3. Productive collision produces transition state 4. Reaction occurs, products are released Naming of Enzymes Enzyme name ends with suffix “- ase .” Name = substrate – action – “ -ase – E.g., glucose phosphory lase is an enzyme that adds a phosphate to glucose. If the “action” is left out of the name, assume the action is hydrolysis. E.g., a prot ease catalyzes the hydrolysis of proteins into oligopeptides or amino acids. Different organs may make different enzymes (isoenzymes) that have the same activity. Differences in structure do not affect the active sites. Enzymes as Catalysts
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Enzymes & Metabolism Heyer 3 Regulation of Enzyme Activity Rate of enzyme-catalyzed reactions measured by the rate that substrates (reactants) are converted to products. Factors regulating enzyme activity: 1. Mass action: concentration of substrates and products. 2. Concentration of enzyme. Gene expression. Post-translational modification. • Proteolysis. 3. Alteration of enzyme structure. • Activation. • Temperature. • pH. 4. Cofactors and Coenzymes. 5. Inhibitors. Reversible Reactions Some enzymatic reactions are reversible. Both forward and backward reactions are catalyzed by same enzyme.
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