1. Enzymes Enzymes are proteins that speed up biological chemical reactions without themselves being used up in the process. Thus they are biological catalysts. They can be used over and over and over again.

4. All chemical reactions involve a change in energy. Either energy needs to be put into a reaction to make it go, which is called an endothermic reaction, or energy is released, which is called an exothermic reaction.

5. All reactions need an input of energy just to get it started. This energy is called the activation energy.

6. Activation Energy

7. SUBSTRATE

9. Enzymes work by lowering the activation energy, making it easier to start the reaction.

11. Remember, an enzyme is a biological catalyst

12. An enzyme fits its substrate like a lock fits a key. An enzyme will work with only one type of substrate.

13. Enzymes are not changed when they catalyze reactions. Therefore they can be used over and over and over again.

14. There are many different types of enzymes in living organisms. Digestive enzymes break down the food you eat. Enzymes in your tears kill bacteria. There is an enzyme in your blood which breaks down the dangerous chemical hydrogen peroxide (H2O2).

15. Enzymes work best at certain temperatures. If enzymes get too hot or too cold the shape will change and the active site will be unable to bind the substrate. The reaction will not proceed. pH is also critical. Enzymes only work within a small range of pH. amount of substrate will change the rate of enzyme activity.