Cells & Enzymes

1. Cells & Enzymes Section 2

2. Catalysts • The rate chemical reaction can be speeded up by raising the temperature or adding a catalyst • A catalyst is not changed by the reaction so it can be re-used • An artificial catalyst used to speed up the breakdown of hydrogen peroxide is manganese dioxide

3. Enzymes • Enzymes are biological catalysts and are found in all living cells • The enzyme that speeds up the breakdown of hydrogen peroxide into water and oxygen is called catalase catalase HYDROGEN PEROXIDE OXYGEN + WATER

4. The Nature of Enzymes • There are thousands of different enzymes working in your body • Why are there so many different enzymes? Each enzyme has its own substrate and no other enzyme can work on that substrate • The substrate of an enzyme is the substance it works on e.g. hydrogen peroxide is the substrate for the enzyme catalase.

5. Lock & Key Theory proteins • Enzymes are made from • An enzyme can only work on it’s own specific substrate • For this reason an enzyme’s action is said to be SPECIFIC • Similar to a lock and key – only one specific key (substrate) will fit into a specific lock (enzyme)

6. Each enzyme has a particular area on its surface called an active site • The active site matches the shape of the enzyme’s substrate so it can join to the enzyme complimentary This substrate will not works with the enzyme because the shape is not complimentary to the enzyme

7. Types of Reactions • Enzymes can be involved in two different types of reactions: • Breakdown (Degradation) Reactions • Building-Up (Synthesis) Reactions

8. Breakdown Reactions • Breakdown or degradation reactions convert large molecules into smaller ones • An example of this is the breakdown of large starch molecules into smaller maltose molecules by amylase • Amylase is found naturally in saliva

9. Breakdown Reactions amylase Starch is broken down by the enzyme .…….… to ……….. sugar molecules STARCH AMYLASE MALTOSE maltose Large starch molecule Small maltose molecules

10. Breakdown Reactions water Hydrogen Peroxide is broken down into ……… and ……….. gas by the enzyme ………… HYDROGEN PEROXIDE CATALASE WATER+OXYGEN • catalase oxygen

11. Breakdown Reactions glucose Sucrose is broken down into ……….. and ………… by the enzyme ………… SUCROSE INVERTASE GLUCOSE + FRUCTOSE fructose • invertase G F S

12. Protein is another large, insoluble, molecule that needs to be broken down into smaller, soluble, units so that it can get across the cell membrane and into our bodies Protein is broken down into polypeptides by the enzyme pepsin Breaking Down Protein Protein pepsin Polypeptides

13. Fats must be broken down into smaller units called fatty acids and glycerol Fats must be broken down so we can absorb them into our bodies The enzyme lipase helps to break down the fats Breaking Down Fats Fats lipase Fatty acids + Glycerol

14. Synthesis Reactions • Build-up or synthesis reactions convert small molecules to larger ones • An example of this is the build up of starch from glucose-1-phosphate molecules

15. The build up of glucose-1-phosphate in plants • Leaves make glucose • Some used as energy for growth • Some transported to root for storage • Once in roots glucose is converted to glucose-1-phosphate • The enzyme phosphorylase converts lots of glucose-1-phosphate into a larger starch molecule Glucose-1-phosphate phosphorylase Starch

16. Phosphorylase Experiment • Aim: to show that starch is being synthesised when the substrate and enzyme are both present

17. Row A: glucose-1-phosphate and phosphorylase Row B: glucose-1-phosphate and distilled water Row C: distilled water and phosphorylase

18. Row A: glucose-1-phosphate and phosphorylase Row B: glucose-1-phosphate and distilled water Row C: distilled water and phosphorylase Row A was the only one that gave a positive result with iodine solution. This means that there was starch present in row A only. This experiment proves that in order to synthesise starch from glucose-1-phosphate and the enzyme phosphorylase must be present.

19. Controls Row A: glucose-1-phosphate and phosphorylase Row B: glucose-1-phosphate and distilled water Row C: distilled water and phosphorylase Rows B and C where used as controls in this experiment to prove that both the enzyme and the substrate were needed together to synthesise starch.

20. Digestive Enzymes • Each enzyme has an optimum pH Mouth = pH 7 amylase Stomach = pH 2 pepsin Small Intestine = pH 9 trypsin Most enzymes that work in the body have an optimum temperature of 37°C

21. The pH Scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14 …. …. Acid Alkali Neutral Strong Acid Weak Acid Weak Alkali Strong Alkali

22. Effects of Temperature • Like you, enzymes like to be at a comfortable temperature to work at their maximum rate • If the temperature is too low, there is not enough energy for the reaction to go • By increasing the temperature, the rate of reaction will increase because there is more energy for the reaction • After a certain temperature, the reaction will start to decrease rapidly to zero

23. Effects of Temperature • When enzymes reach a particular temperature, they will work at their maximum capacity. • The temperature at which an enzyme works best is known as the optimum temperature. • If the temperature continues to rise, the enzyme’s shape will eventually be destroyed. We say that the enzyme has been denatured.

24. Effects of Temperature

25. Denaturing • If an enzyme is denatured it’s shape will change • Enzyme will no longer be complimentary to the shape of the substrate • Excessive heat can cause an enzyme to be denatured 37°C 60°C