1. Enzymes

2. Most chemical reactions require energy to begin
The amount of energy needed to start the reaction is called activation energy 2

3. Biological catalysts are called enzymes
Certain chemical substances (catalysts) reduce the amount of activation energy required
Biological catalysts are called enzymes 3

4. Enzymes are an important class of catalysts in living organisms
Mostly protein
Thousands of different kinds
Each specific for a different chemical reaction 4

5. Enzyme Structure Enzymes work on substances called substrates
Substrates must fit into a place on an enzyme called the active site
Enzymes are reusable! 5