1. 3.3 & 3.4 Enzymes Lecture Radjewski

2. Biology, Sixth Edition Chapter 6, Energy and Metabolism Enzymes Enzymes are protein catalysts enormously speed up reactions. often have an “-ase” ending to their name. – e.g., hexokinase, catalase, peptidase, mutase Enzymes: 1.Lower the activation energy 2.Do not add or remove energy 3.Do not change the equilibrium 4.Are reused over and over

3. Biology, Sixth Edition Chapter 6, Energy and Metabolism

4. Enzymes Lower E A 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!

5. Biology, Sixth Edition Chapter 6, Energy and Metabolism A Catalytic Cycle Active Site

7. Biology, Sixth Edition Chapter 6, Energy and Metabolism Some enzymes require ions or other molecules to function Cofactor(s) -- an inorganic component, often an ion such as Ca 2+ or Mg 2+ 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

8. Biology, Sixth Edition Chapter 6, Energy and Metabolism Enzymes are Very Sensitive Each enzyme has an optimal temperature, pH, and ionic strength

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

11. Biology, Sixth Edition Chapter 6, Energy and Metabolism Enzyme Inhibition Two types: Competitive: Inhibitor binds at the active site Noncompetitive: Inhibitor binds at a site distant from the active site

14. Biology, Sixth Edition Chapter 6, Energy and Metabolism 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

15. 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