1. METABOLISM

2. The concept of metabolism Metabolism = all the chemical reactions taken place inside the living organisms Metabolic reactions produce different life processes, e.g. –photosynthesis –respiration –movement –growth –reproduction

3. Types of metabolism Catabolism : –breaking down of complex organic molecules into simpler molecules, e.g. respiration

4. Types of metabolism Anabolism –building up of complex organic molecules from simple molecules, e.g. photosynthesis

5. Control of metabolism Metabolic reactions can be controlled and speeded up by enzymes –metabolic reactions would be too slow to occur if no enzymes are present!

6. Mechanism of enzyme action Each enzyme has an active site

7. Mechanism of enzyme action Place where substrate binds with the enzyme Each enzyme only allows its specific substrate to fit with its active site exactly

8. The enzyme and substrate molecules combine to form a temporary structure called enzyme-substrate complex Mechanism of enzyme action

9. The product molecules are then formed and they escape from the active site Mechanism of enzyme action

10. The product molecules are then formed and they escape from the active site Mechanism of enzyme action The active site is free to attach to other substrate molecules

11. This hypothesis to explain the specificity of enzyme action is called

12. Biological catalyst Nature and properties of enzymes Proteins in nature Specific in action –one kind of enzyme will catalyse only one kind of chemical reaction Biological found within living organisms catalyst substance which can speed up a chemical reaction

13. Nature and properties of enzymes Catalyse reversible reaction in both directions Action affected by temperature and pH –high temperature and extreme pH can denature enzymes  protein in nature

14. Effect of temperature on enzyme activity Low temperature : low kinetic energy possessed by the substrate and enzyme molecules  Lower reaction rate (and enzyme activity) The enzyme becomes inactive

15. Effect of temperature on enzyme activity Higher temperature : more kinetic energy possessed by the substrate and enzyme molecules  Higher reaction rate (and enzyme activity)

16. Effect of temperature on enzyme activity The temperature which allows the highest enzyme activity is called the optimum temperature

17. Effect of temperature on enzyme activity At temperature higher than the optimum temperature, the shape of the active site is changed  substrate can no longer bind to the active site of the enzyme The enzyme is said to be denatured

18. Graph showing effect of temperature on enzyme activity

19. Effect of temperature on enzyme activity Enzymes become inactive but not denatured at low temperatures  They can regain catalytic function when the temperature increases

20. Effect of temperature on enzyme activity Denaturation is a permanent process  When an enzyme is denatured, its catalytic function is lost permanently, and cannot be restored even it is put in lower temperature

21. Effect of temperature on enzyme activity Different enzymes may have different optimum temperature The optimum temperature of many enzymes in human body is not 37 o C, even though this is our body temperature! –Our body temperature can provide a better environment for the enzymes in our bodies to work

22. Effect of pH on enzyme activity Optimum pH : the pH value at which the enzyme has the highest activity Different enzymes may have different optimum pHs pH of medium higher or lower than optimum pH can denature the enzyme