3. An enzyme is a biological catalyst. Enzymes are found in all living cells. Catalase is an enzyme which causes the breakdown of hydrogen peroxide Hydrogen peroxide Water + Oxygen Catalase Enzyme

6. Enzyme action is said to be specific. That means an enzyme can only work on one specific substrate Hydrogen peroxide Water + Oxygen Catalase Hydrogen peroxide Amylase

7. Lock and Key Idea The active site of an enzyme is the place on its surface which is complementary in shape to it’s substrate Substrate e.g. Hydrogen Peroxide Enzyme e.g. Catalase Active sites

8. Enzyme activity Animations-click to view

10. A BREAKDOWN reaction is one in which an ENZYME breaks down it’s substrate into SMALLER molecules. Starch is an energy rich compound which must be broken down into smaller molecules to be absorbed into the blood stream. An enzyme called AMYLASE (found in saliva) is the first stage of this breakdown. Starch Maltose Amylase Enzyme

11. Carbohydrates G G G G G G Starch (insoluble) G G G G Maltose Amylase action

12. Iodine Testing for Starch Benedicts Testing for Maltose + - + -

14. Starch Storage in Potato Plants Glucose converted to glucose-1-phosphate Some glucose transported to roots Some glucose used for energy by shoots and young leaves or stored in fruit Glucose is made in leaves by photosynthesis An enzyme called Phosphorylase joins these molecules to produce STARCH

15. Phosphorylase is an enzyme which SYNTHESISES starch In a synthesis reaction the substrate molecules are built up into larger molecules Glucose-1-phosphate Starch Phosphorylase

16. Starch Synthesis Experiment Row A Substrate + enzyme Row B Substrate + water Row C Enzyme + Water 5 min 10 min 15 min 20 min Iodine added

18. The OPTIMUM temperature for an enzyme is the temperature at which it works best . The optimum temperature for most human enzymes is: 37°C = body temperature

19. Enzyme activity Denaturing-click to view A DENATURED enzyme is an enzyme that has lost its natural structure permanently and no longer works. Remember ! An enzyme is NEVER dead , dying or killed !!!!!!

21. The pH Scale Neutral Acidic Alkali Stomach pH 2 Mouth pH 7 Small Intestine pH 9

22. How do changes in pH affect this breakdown reaction? Invertase G F Sucrose G F Glucose Fructose (substrate) (products)

23. The OPTIMUM pH for an enzyme is the pH at which it works best . Each enzyme of the digestive system has a different optimum pH depending on its site of action.