Chapter 5   enzymes
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  • Figure 5.1 page 73
  • Figure 5.1 page 73
  • Figure 5.1 page 73
  • Figure 5.1 page 73
  • Figure 5.1 page 73
  • Figure 5.6 page 77
  • Figure 5.6 page 77
  • Figure 5.6 page 77
  • Figure 5.7 page 80
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87
  • Concept Map page 87

Chapter 5 enzymes Presentation Transcript

  • 1. Chapter 5 - Enzymes
    • 5.1 What Are Enzymes?
    • 5.2 Classification of Enzymes
    • 4.3 Characteristics of Enzymes
  • 2. Learning Objectives
    • Candidates should be able to:
    • Define enzymes as proteins which function as biological catalysts.
  • 3. 5.1 What Are Enzymes ?
    • Enzymes are:
    • Biological catalysts,
    • Protein in nature,
    • Catalyze chemical reactions without being changed at the end of the reaction.
  • 4. Enzymes as catalysts
    • Enzymes lower the activation energy of a reaction so that it occurs more readily .
  • 5. Activation Energy Imagine a chemical reaction as the process of rolling a huge stone ( reactant ) up a hill so that it rolls down and breaks into tiny pieces ( products ). 1
  • 6. Activation Energy Activation energy is the energy needed to roll the stone up the hill. Imagine a chemical reaction as the process of rolling a huge stone ( reactant ) up a hill so that it rolls down and breaks into tiny pieces ( products ). 1 2
  • 7. Activation Energy Once over the hill, the rest of the reaction occurs. Imagine a chemical reaction as the process of rolling a huge stone ( reactant ) up a hill so that it rolls down and breaks into tiny pieces ( products ). 1 Activation energy is the energy needed to roll the stone up the hill. 2 3
  • 8. Activation Energy Imagine a chemical reaction as the process of rolling a huge stone ( reactant ) up a hill so that it rolls down and breaks into tiny pieces ( products ). 1 Activation energy is the energy needed to roll the stone up the hill. 2 Once over the hill, the rest of the reaction occurs. 3 The stone rolls down and breaks into tiny pieces (products are formed). 4
  • 9. Activation Energy The stone rolls down and breaks into tiny pieces (products are formed). The energy needed to start a chemical reaction is called activation energy. Imagine a chemical reaction as the process of rolling a huge stone ( reactant ) up a hill so that it rolls down and breaks into tiny pieces ( products ). 1 Activation energy is the energy needed to roll the stone up the hill. 2 Once over the hill, the rest of the reaction occurs. 3 4 5
  • 10. Digestion: An Enzyme-Catalysed Process
    • Why do we need to digest our food?
    • Starch, proteins and fats are very large.
    • They cannot diffuse across cell membranes for absorption.
    • Therefore, they must be digested into
      • Simpler, smaller and soluble substances.
      • Diffusible across cell membranes.
  • 11. Other applications of Enzymes
    • Anabolic processes
      • Eg. Synthesis of proteins from amino acids.
    • Catabolic processes
      • Eg. Oxidation of glucose (tissue respiration)
    • Catalase production
      • Catalase catalyses the breakdown of toxic hydrogen peroxide into harmless water and oxygen.
      • Catalase is abundant in liver and blood.
  • 12. 5.2 Classification of Enzymes
    • Enzymes are classified
    • according to the chemical reaction involved in:
      • Enzymes that catalyse hydrolysis reactions are called hydrolases.
        • Example of hydrolases:
        • Carbohydrases, proteases, lipases .
      • Enzymes involved in oxidation of food as called oxidation-reduction enzymes.
  • 13. Learning Objectives
    • Candidates should be able to:
    • Explain enzyme action in terms of the ‘lock and key’ hypothesis.
    • Investigate and explain the effects of temperature and of pH on the rate of enzyme catalyzed reactions .
  • 14. 5.3 Characteristics of Enzymes
    • Enzymes alter or speed up the rates of chemical reaction that occur in a cell.
    • Enzymes are required in minute amounts .
      • Since enzymes are not altered in a chemical reaction, a small amount can catalyse a huge reaction.
  • 15. Enzymes are specific
    • Specificity of enzyme is due to its shape (or surface configuration).
    • The substrate will fit into an enzyme, forming an enzyme-substrate complex .
    • The product will then be released.
  • 16. Lock and key hypothesis
    • What is the ‘lock and key’ hypothesis?
    • It is the old view of enzyme specificity, that there was an exact match between the active site and the substrate.
  • 17. A synthesis reaction
  • 18. Lock and Key Hypothesis active sites A B enzyme molecule (the ‘lock’) substrate molecules ( A and B) can fit into the active sites
  • 19. Lock and Key Hypothesis active sites A B enzyme molecule (the ‘lock’) enzyme-substrate complex substrate molecules ( A and B) can fit into the active sites
  • 20. Lock and Key Hypothesis active sites A B AB enzyme molecule (the ‘lock’) enzyme-substrate complex substrate molecules ( A and B) can fit into the active sites enzyme molecule is free to take part in another reaction a new substance (product) AB leaves the active sites
  • 21. Induced fit hypothesis
    • What is induced fit hypothesis?
    • shape of the active site adjusts to fit the substrate.
  • 22. Induced fit hypothesis
    • How did induced fit hypothesis come about?
    • - recent imaging technology demonstrated changes in the 3-D conformation of enzymes when interacting with their substrates.
  • 23. Effect of temperature
    • At low temp:
      • Rate of reaction is slow.
      • Enzymes are inactive at low temp .
      • Every 10 o c rise in temp, rate of reaction increases by double
      • (till it reaches optimum temp).
  • 24. Effect of temperature
    • At optimum temp:
      • Rate of reaction is the highest .
      • Enzymes are most active .
    • Beyond optimum temp:
      • Rate of enzyme activity decreases sharply.
      • Enzymes are being denatured.
      • Hydrogen bonds are easily disrupted by increasing temperature .
  • 25. Effect of temperature
  • 26. Effect of Temperature on the Rate of Reaction Temperature Rate of reaction (enzyme activity) 0 K (optimum temperature) D At point D , the enzyme has lost its ability to catalyse the reaction. An enzyme is less active at very low temperatures. 1 As the temperature rises, enzyme activity increases as indicated by the increase in the rate of reaction it catalyses. Usually the enzyme is twice as active for every 10°C rise in temperature until the optimum temperature is reached. 2 The optimum temperature is reached. Enzyme is most active. 3 Beyond the optimum temperature, enzyme activity decreases. 4 5
  • 27. Effect of pH
    • Enzymes have an optimum pH .
    • Deviation from the optimum pH will decrease enzyme activity .
  • 28. Effect of pH on Enzyme Activity
  • 29. Effects of substrate and enzyme concentration on rate of reaction
    • Increasing substrate concentration will increase rate of reaction until a certain limit.
    • Cause:
      • Enzyme molecules are saturated .
    • Enzyme concentration is now the limiting factor.
  • 30. What is a limiting factor?
    • Any factor that directly affects the rate of a process if its quantity is changed
    • The value of the limiting factor has to be increased in order to increase the rate of the process .
  • 31. Coenzymes
    • What are coenzymes?
    • Some enzymes require a coenzyme to be bound to them before they can catalyse reactions .
    • Usually, coenzymes are non-protein organic compounds .
      • Eg. Vitamins, especially the B complex vitamins.
  • 32. Coenzymes
    • Coenzymes are altered in some way by participating in enzyme reaction.
  • 33. Enzymes
    • catalyse reversible reactions
    A D B C + + reactants products reactants reactants
  • 34. Enzymes Characteristics Functions Mode of Action Limiting factors affected by
  • 35. Enzymes
  • 36. Enzymes Biological catalysts, which are mainly made of proteins. They speed up the rate of chemical reactions without themselves being chemically changed at the end of the reactions.
  • 37. Enzymes Functions
  • 38. Enzymes Functions
    • Building up or synthesising complex substances
    • Breaking down food substances in cells to release energy (cellular respiration)
    • Breaking down poisonous substances in cells
  • 39. Enzymes Characteristics Functions
  • 40. Enzymes Characteristics Functions
    • Speed up chemical reactions
    • Required in small amounts
    • Highly specific
    • Work best at an optimum temperature and pH
    • May need coenzymes for activity
    • Some catalayse reversible reactions
  • 41. Enzymes Characteristics Functions Mode of Action
  • 42. Enzymes Characteristics Functions Mode of Action
    • Lower the activation energy of a reaction
    • Interact with the substrate according to lock and key hypothesis to form an enzyme-substrate complex
  • 43. Enzymes Characteristics Functions Mode of Action affected by
  • 44. Enzymes Characteristics Functions Mode of Action Limiting factors Factors that directly affect the rate at which a chemical reaction occurs if their quantity is changed. The value of a limiting factor must be increased in order to increase the rate of reaction. affected by
  • 45. Enzymes Characteristics Functions Mode of Action Limiting factors Temperature / pH e.g. affected by
  • 46. Enzymes Characteristics Functions Mode of Action Limiting factors Temperature / pH e.g.
    • Increase in temperature increases the rate of enzyme reaction until optimum temperature is reached
    • Increase in pH increases the rate of enzyme reaction until optimum pH is reached
    affected by
  • 47. Enzymes Characteristics Functions Mode of Action Limiting factors Temperature / pH e.g. Classes affected by
  • 48. Enzymes Characteristics Functions Mode of Action Limiting factors Temperature / pH e.g. Classes based on the type of reaction catalysed e.g. Hydrolases affected by
  • 49. Enzymes Characteristics Functions Mode of Action Limiting factors Temperature / pH e.g. Classes based on the type of reaction catalysed e.g. Hydrolases Oxidation-reduction enzymes affected by