Living Cells

1. Living Cells Enzymes Mr G Davidson

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

3. Introduction to Enzymes • We can speed up some chemical reactions by: • Increasing the temperature • Adding a catalyst • Since it is not always appropriate to increase the temperature of a living organism, biological catalysts called ENZYMES are used to increase the rate of reactions. Mr G Davidson

4. Catalysts • A catalyst is a substance which can speed up a reaction without itself being altered in the reaction. • When a catalyst is present, the reaction requires less energy to start it; activation energy . • When a catalyst is present the reaction is quicker. • A catalyst remains unchanged in the reaction and can be re-used. Mr G Davidson

5. Hydrogen peroxide Water + Oxygen (H2O2) (H2O) (O2) Breakdown of Hydrogen Peroxide • Hydrogen peroxide (H2O2) is a harmful by-product of reactions inside cells. • H2O2 can be broken down into waterH2Oand oxygenO2. Mr G Davidson

6. Breakdown of Hydrogen Peroxide • Hydrogen peroxide can be broken down to water and oxygen by increasing the temperature. • If it is placed in water baths of increasing temperatures, the number of bubbles of oxygen released increases with temperature. Mr G Davidson

7. Biological Catalysts • Enzymes are biological catalysts. • Catalase is an enzyme, made by living cells, which can break down hydrogen peroxide. • If we add a piece of living tissue to hydrogen peroxide, we can see bubbles of oxygen being released. • The more bubbles released, the more catalase there is in the tissue. Mr G Davidson

8. Specificity • Catalase can only speed up the breakdown of hydrogen peroxide, not any other reaction. • It is said to be specific. • Each enzyme catalyses only one reaction. • The substance the enzyme catalyses is called the substrate. Mr G Davidson

9. Specificity • All enzymes are made of protein. • Enzymes have an area on their surface which is a specific shape, and it is here that the substrate attaches. • This area is called the active site. Mr G Davidson

10. Specificity • The enzyme’s shape and the substrate’s shape are said to be complimentary. • The substrate locks onto the enzyme at the active site and the reaction occurs. • This is called the Lock and Key Theory. Mr G Davidson

11. Specificity • The reaction produces the products. • Some enzymes are responsible for breaking down large substrates into smaller products, while others are responsible for the building up of large products from smaller substrates. Mr G Davidson

12. Substrate Active site Enzyme Lock & Key Theory Product Product Mr G Davidson

13. Starch & Amylase • Starch is a carbohydrate. • It contains energy and is found in many foods. • Starch molecules are very large and cannot pass through cell membranes. • Therefore, they need to be broken down to smaller molecules. Mr G Davidson

14. Starch & Amylase • This is done by an enzyme called AMYLASE. • Amylase is found in our saliva. • The starch is broken down to molecules of a sugar called maltose. AMYLASE STARCH MALTOSE (Enzyme) (Substrate) (Product) Mr G Davidson

15. Starch molecule Maltose molecules Starch & Amylase Mr G Davidson

16. Controls • When we carry out any experiment, it is important to have a control. • The control allows us to make a valid comparison. • e.g. if we are testing the action of amylase by putting it in starch solution, a control would be to have another tube and put water in the starch solution. • This way we know it is the amylase that is responsible for the changes that occur. Mr G Davidson

17. Synthesis Reactions • So far, we have looked at enzymes which break down molecules, e.g. amylase breaks down starch. • How is the starch built up in the first place? • Plants make glucose using sunlight. • This glucose is converted to glucose-1-phosphate. Mr G Davidson

18. Synthesis Reactions • An enzyme called PHOSPHORYLASE is used to join glucose-1-phosphate molecules together to make starch. • This is called a synthesis reaction. PHOSPHORYLASE GLUCOSE-1-PHOSPHATE STARCH (Enzyme) (Substrate) (Product) Mr G Davidson

19. Synthesis Reactions • There are many other synthesis enzymes which allow organisms to build up structural molecules as well as storage molecules, e.g. • The liver converts excess glucose to glycogen for storage. • Skin cells convert amino acids into collagen which allows the skin to be flexible but tough. Mr G Davidson

20. Temperature and Enzymes • Enzymes are affected by a change in temperature. • If the temperature is particularly low, the enzyme activity will be very slow. • As the temperature increases the enzyme activity increases, but only up to a certain point. Mr G Davidson

21. Temperature and Enzymes • The temperature at which the enzyme works at its quickest is called the Optimum temperature. • Most human enzymes have an optimum temperature around 37oC • Once the temperature is too high the enzyme (being a protein) is damaged and we say it has been denatured. Mr G Davidson

22. Optimum temperature Increasing enzyme activity Enzyme being denatured Increasing rate of Reaction 40 50 0 30 10 20 Temperature (oC) Temperature v Enzyme Activity Mr G Davidson

23. Effect of pH on Enzymes • pH is a measure of how acid or alkali something is. • The pH scale goes from 1 to 14, with 1 being very acidic, 14 being very alkaline and 7 being neutral. • The shape of an enzyme can be affected by changes in pH and this will affect how well the enzymes work. Mr G Davidson

24. Effect of pH on Enzymes • Like temperature, enzymes have an optimum pH, i.e. a pH when they are most efficient. • The optimum pH varies from enzyme to enzyme. • Our digestive system has a range of pH’s as the food passes through it, and this creates ideal conditions for specific enzymes. Mr G Davidson

25. 100 80 Pepsin 60 Catalase Enzyme Activity (%) Lipase 40 20 0 0 1 2 3 4 5 6 7 8 9 10 11 12 pH Effect of pH on Enzymes Mr G Davidson