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.

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

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

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

28. Effect of pH on Enzyme Activity

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

39. Enzymes Characteristics Functions

41. Enzymes Characteristics Functions Mode of Action

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

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