1. Enzymes

2. Introduction to Enzymes  Chemical reactions all occur at different rates  Some are very quick and some are extremely slow

3. Introduction to Enzymes We can speed up some chemical reactions by: 1. increasing the temperature 2. adding a catalyst Since it is not always appropriate increasing the temperature of a living organism, biological catalysts called ENZYMES are used to increase the rate of reaction.

4. Enzymes An enzyme is a substance which can speed up a reaction without itself being altered. There are 3 important points that are true for all enzymes and catalysts: 1.When an enzyme is present, the reaction requires less energy to start. 2.When an enzyme is present, the reaction is quicker 3.An enzyme remains unchanged during the reaction and can be reused.

5. Breakdown of Hydrogen Peroxide Hydrogen Peroxide (H ₂ O ₂ ) is a harmful by-product of reactions inside cells. H ₂ O ₂ can be broken down into water (H ₂ O) and oxygen (O ₂ ). Hydrogen peroxideWater + Oxygen (H 2 O 2 ) (H 2 O) (O 2 ) Hydrogen peroxideWater + Oxygen (H 2 O 2 ) (H 2 O) (O 2 )

6. Enzymes Enzymes are biological catalysts Catalase is an enzyme made by living cells, which can breakdown hydrogen peroxide When a piece of living tissue is added, you can see bubbles of oxygen released The more bubbles released, the more catalase is present in the tissue.

7. Questions 1.What is meant by activation energy? 2.State 3 properties of a catalyst. 3.Where are enzymes found in living organisms? 4.Of what type of organic substance are enzymes composed? 5.Briefly explain why enzymes are needed for the functioning of all living cells.

8. Enzymes Catalase can only speed up the breakdown of hydrogen peroxide, NO OTHER REACTION. It is said to be specific Each enzyme can catalyse only one reaction The substance that the enzyme catalyses is called the substrate

9. Enzymes Enzymes have an area on their surface which is a specific shape. It is here that the substrate attaches. This area is known as the active site. The shape of the active site is determined by its chemical structure which results from bonding between amino acids in the enzyme molecule.

10. Enzymes The active site and substrate are said to be complementary The substrate locks onto the enzyme at the active site and the reaction occurs. This is known as the ‘lock and key’ theory.

12. Enzymes The reaction produces the products of the reaction. Some enzymes are responsible for breaking down large substrates into small products Some enzymes are responsible for building up small substrates into large products

13. Questions 1.What determines the shape of an enzymes active site? 2.What name is given to the substance on which an enzyme acts? 3.Why is an enzyme said to be specific? 4.How is an enzyme thought to act according to the lock and key hypothesis?