Enzymes are proteins that catalyze chemical reactions without being altered themselves. They speed up reactions by lowering activation energy. Enzymes work most efficiently at a specific temperature and pH, and require cofactors to function. Enzyme activity is affected by substrate, temperature, pH, and other limiting factors. Enzymes are classified based on the type of reaction they catalyze, such as hydrolysis or oxidation-reduction.

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