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  1. 1. Chapter 4 Enzymes and Energy www.freelivedoctor.com
  2. 2. Enzymes <ul><li>Biological catalysts. </li></ul><ul><li>Increase rate of chemical reactions. </li></ul><ul><li>Most enzymes are proteins with diverse structure. </li></ul>www.freelivedoctor.com
  3. 3. Biological Catalyst <ul><li>Chemical that: </li></ul><ul><ul><li>Increases the rate of a reaction. </li></ul></ul><ul><ul><li>Is not changed at the end of the reaction. </li></ul></ul><ul><ul><li>Does not change the nature of the reaction or final result. </li></ul></ul><ul><ul><li>Lowers the activation energy required. </li></ul></ul><ul><li>Activation energy: </li></ul><ul><ul><li>Amount of energy required for a reaction to proceed. </li></ul></ul>www.freelivedoctor.com
  4. 4. Activation Energy www.freelivedoctor.com
  5. 5. Mechanism of Enzyme Action <ul><li>Each type of enzyme has has a characteristic 3-dimensional shape (conformation). </li></ul><ul><li>Has ridges, grooves, pockets lined with specific amino acids. </li></ul><ul><li>Pockets active in catalyzing a reaction are called the active sites of the enzyme. </li></ul>www.freelivedoctor.com
  6. 6. Mechanism of Enzyme Action <ul><li>Lock-and-key model of enzyme activity: </li></ul><ul><li>Reactant molecules ( substrates ) have specific shapes to fit into the active sites. </li></ul><ul><ul><li>Substrate fits into active sites in enzyme. </li></ul></ul><ul><ul><li>Enzyme-substrate complex dissociates. </li></ul></ul><ul><ul><li>Products of reaction formed and free enzyme. </li></ul></ul>www.freelivedoctor.com
  7. 7. www.freelivedoctor.com
  8. 8. Naming of Enzymes <ul><li>Enzyme name ends with ase . </li></ul><ul><li>Classes of enzymes named according to activity. </li></ul><ul><li>Enzymes that have the same activity in different organs may make different models called isoenzymes. </li></ul>www.freelivedoctor.com
  9. 9. Control of Enzyme Activity <ul><li>Rate of enzyme-catalyzed reactions measured by the rate substrates are converted to products. </li></ul>www.freelivedoctor.com
  10. 10. Control of Enzyme Activity <ul><li>Factors influencing rate: </li></ul><ul><ul><li>Temperature </li></ul></ul><ul><ul><li>pH </li></ul></ul><ul><ul><li>[cofactors and coenzyme] </li></ul></ul><ul><ul><li>[enzyme and substrate] </li></ul></ul><ul><ul><li>Stimulatory and inhibitory effects of products </li></ul></ul>www.freelivedoctor.com
  11. 11. Effect of Temperature <ul><li>Increase in temperature increases rate of reaction. </li></ul><ul><li>At body temperature, plateaus. </li></ul><ul><li>Denature at high temperatures. </li></ul>www.freelivedoctor.com
  12. 12. pH <ul><li>Each enzyme exhibits peak activity at narrow pH range ( pH optimum ). </li></ul><ul><li>Optimum pH reflects the pH of the body fluid in which the enzyme is found. </li></ul>www.freelivedoctor.com
  13. 13. Cofactors and Coenzymes <ul><li>Cofactor: </li></ul><ul><ul><li>Attachment of cofactor causes a conformational change in enzyme. </li></ul></ul><ul><ul><li>Participate in temporary bonds between enzyme and substrate. </li></ul></ul><ul><li>Coenzymes: </li></ul><ul><ul><li>Cofactors that are organic molecules derived from niacin, riboflavin and other H 2 0 soluble vitamins. </li></ul></ul>www.freelivedoctor.com
  14. 14. www.freelivedoctor.com
  15. 15. Substrate Concentration <ul><li>Rate of product formation will increase as the [substrate]. </li></ul><ul><li>Plateau of maximum velocity occurs when enzyme is saturated. </li></ul>www.freelivedoctor.com
  16. 16. Reversible Reactions <ul><li>H 2 0 + C0 2 H 2 C0 3 </li></ul><ul><li>Direction of reversible reaction depends on the concentration of molecules to the left and right of the arrows. </li></ul>ca www.freelivedoctor.com
  17. 17. <ul><li>Sequence of enzymatic reactions that begins with initial substrate, progresses through intermediates and end with a final product. </li></ul>www.freelivedoctor.com
  18. 18. <ul><li>An intermediate can serve as substrate for 2 different enzymes, producing 2 different products. </li></ul>www.freelivedoctor.com
  19. 19. Negative feedback inhibition. One of the final products inhibits the activity of the branch enzyme. Prevents final product accumulation. www.freelivedoctor.com
  20. 20. Inborn Errors of Metabolism <ul><li>Inherited defect in a gene. </li></ul><ul><li>Quantity of intermediates formed prior to the defect increases. </li></ul><ul><li>Final product decreases, producing a deficiency. </li></ul>www.freelivedoctor.com
  21. 21. Cannot produce tyrosine, PKU results. Cannot produce melanin, albinism results. www.freelivedoctor.com
  22. 22. Bioenergetics <ul><li>Flow of energy in living systems. </li></ul><ul><li>1 st law of thermodynamics: </li></ul><ul><ul><li>Energy can be transformed, but it cannot be created or destroyed. </li></ul></ul><ul><li>2 nd law of thermodynamics: </li></ul><ul><ul><li>Energy transformations increase entropy. </li></ul></ul><ul><ul><li>Free energy can be used to do work. </li></ul></ul>www.freelivedoctor.com
  23. 23. Endergonic Reactions <ul><li>Chemical reactions that require an input of energy. </li></ul><ul><li>Products must contain more free energy than reactants. </li></ul>www.freelivedoctor.com
  24. 24. Exergonic Reactions <ul><li>Convert molecules with more free energy to molecules with less. </li></ul><ul><li>Release energy in the form of heat. </li></ul><ul><li>Heat is measured in calories . </li></ul><ul><li>Calorie: </li></ul><ul><ul><li>Amount of heat to raise the temperature of one cubic centimeter of H 2 0 one degree Celsius. </li></ul></ul>www.freelivedoctor.com
  25. 25. www.freelivedoctor.com
  26. 26. www.freelivedoctor.com
  27. 27. Coupled Reactions: ATP <ul><li>Cells cannot use heat for energy. </li></ul><ul><li>Require energy released in exergonic reactions (ATP) to be directly transferred to chemical-bond energy in the products of endergonic reactions. </li></ul>www.freelivedoctor.com
  28. 28. Universal energy carrier of the cell. www.freelivedoctor.com
  29. 29. Oxidation-Reduction <ul><li>Reduced: </li></ul><ul><ul><li>Molecule/atom gains electrons. </li></ul></ul><ul><li>Reducing agent: </li></ul><ul><ul><li>Molecule/atom that donates electrons. </li></ul></ul><ul><li>Oxidized: </li></ul><ul><ul><li>Molecule/atom loses electrons. </li></ul></ul><ul><li>Oxidizing agent: </li></ul><ul><ul><li>Molecule/atom that accepts electrons. </li></ul></ul><ul><li>May involve the transfer of H + rather than free electrons. </li></ul>www.freelivedoctor.com
  30. 30. Reduced form. www.freelivedoctor.com
  31. 31. Oxidized form. www.freelivedoctor.com