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3.3 & 3.4 Enzymes

Learn about enzymes, protein catalysts that speed up reactions, their role in lowering activation energy, and how they are affected by factors like temperature and pH. Discover the different types of enzyme inhibition and the importance of commitment steps in metabolic pathways.

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3.3 & 3.4 Enzymes

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  1. 3.3 & 3.4 Enzymes Lecture Radjewski

  2. Enzymes • Enzymes are protein catalysts • enormously speed up reactions. • often have an “-ase” ending to their name. • e.g., hexokinase, catalase, peptidase, mutase • Enzymes: • Lower the activation energy • Do not add or remove energy • Do not change the equilibrium • Are reused over and over

  3. Enzymes Lower EA Activation energy (Ea) is the energy required to break the bonds to begin the reaction Example: A molecule of sucrose in solution may hydrolyze in about 15 days; with sucrase present, the same reaction occurs in 1 second!

  4. A Catalytic Cycle Substrates (reactant) ES Complex Induced fit Active Site enzyme product -> now available to catalyze again enzyme

  5. Some enzymes require ions or other molecules to function • Cofactor(s) -- an inorganic component, often an ion such as Ca2+ or Mg2+ • Coenzymes – an organic component • Vitamins • ATP, NADH • Coenzyme A • Prostethic groups – distinctive non-amino acid atoms that permanently bind to their enzymes • Heme • Flavin • Retinal

  6. Enzymes are Very Sensitive • Each enzyme has an optimal temperature, pH, and ionic strength

  7. High temperatures rapidly denature enzymes and this is not reversible • If pH is altered, enzymes become inactive and is not reversible

  8. Enzyme Inhibition • Two types: • Competitive: • Inhibitor binds at the active site • Noncompetitive: • Inhibitor binds at a site distant from the active site

  9. Allosteric Control • If a substance binds to an allosteric site (another region besides the active site), the conformation of the active site is changed and this affects enzyme activity

  10. Metabolic pathways: The first reaction is the commitment step—other reactions then happen in sequence. Feedback inhibition(end-product inhibition)—the final product acts as a noncompetitive inhibitor of the first enzyme, which shuts down the pathway. Commitment Step

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