Investigating Cells

1. Investigating Cells Enzymes Mr G Davidson

2. Hydrogen peroxide (H2O2) Water (H2O) + Oxygen (O) Investigating Enzymes • Most chemical reactions occur very slowly at normal temperatures e.g. hydrogen peroxide breaks down very slowly at room temperature. G Davidson

3. Investigating Enzymes • If the temperature is increased the reaction speeds up, however this is not possible with living organisms. • Therefore, a special chemical called a catalyst is used to speed the reaction up. • Biological catalysts are called ENZYMES. • Living cells produce enzymes to speed up reactions within the cells. G Davidson

4. Investigating Hydrogen peroxide • CATALASE is an enzyme which breaks down hydrogen peroxide to water and oxygen. • If the enzyme is working properly, bubbles of oxygen are released. G Davidson

5. Living Tissue Dead Tissue Control Each test tube contains 20ml hydrogen peroxide G Davidson

6. Investigating Hydrogen peroxide • Results: The living tissues all produce bubbles, but the dead tissue doesn’t. • Conclusion: Living tissues contain catalase which breaks down hydrogen peroxide. G Davidson

7. Catalysts and Enzymes • Catalysts are not changed by the reactions that they are acting on and so can be used again. • There are many chemical reactions occurring in living cells at any one time. G Davidson

8. Catalysts and Enzymes • With the help of catalysts – enzymes, because the temperature is so low, these reactions would occur so slowly that life would be impossible. • Enzymes themselves are NOT living – they are chemicals made of PROTEIN. G Davidson

9. Catalysts and Enzymes • It is possible to extract enzymes from living cells, and once this is done they can be dried and stored in powdered form. • Most enzymes act within the cells in which they are produced. G Davidson

10. Catalysts and Enzymes • A small number do, however, work outside the cells, e.g. digestive enzymes. • Some of the chemical reactions in living organisms involve the building up of large molecules. • Others involve the breakdown of large, complex molecules into smaller simpler ones. G Davidson

11. AMYLASE STARCH SUGAR Amylase • Starch is a large molecule made of hundreds of smaller glucose molecules joined together. • An enzyme called amylase can break down starch and turn it into sugar. G Davidson

12. Testing Amylase • Object: to investigate the enzyme amylase. • Method: • 1. Add 10ml starch solution to a test tube. • 2. Add 2ml amylase solution. • 3. Shake the tube to mix. • 4. Test a drop for starch using iodine solution. • 5. Test a drop for starch every 1 minute. • Results: • Conclusion: The iodine solution does NOT turn blue/black. Amylase breaks down starch to sugar. G Davidson

13. Specificity • Other enzymes act on different substances (SUBSTRATES) and so have no effect on starch. • Each enzyme acts only on a specific substrate; other substances are not affected. • The substance produced as a result of the reaction catalysed by an enzyme is called the PRODUCT. G Davidson

14. Specificity G Davidson

15. Synthesis of Starch • Starch may be synthesised from glucose. • An enzyme is used to speed up the synthesis of starch. • Potatoes contain large amounts of starch. • Potato extract contains the enzyme phosphorylase which speeds up starch synthesis. PHOSPHORYLASE GLUCOSE-1-PHOSPHATE STARCH G Davidson

16. A B C D Synthesis of Starch • Object: To investigate the enzyme phosphorylase. • Method: Set up the following: 1. Test the potato extract for the presence of starch. 2. Put 2 spots of glucose-1-phosphate into each of the hollows. 3. Add a drop of potato extract to each hollow and start the clock. G Davidson

17. Synthesis of Starch • After 4 minutes test A for the presence of starch. • After the next 4 minutes test B and so on. • Results: • Conclusion: G Davidson

18. Pepsin Activity • The activity of an enzyme is affected by the pH of its surrounding medium. • Pepsin is an enzyme produced in the stomach. • It speeds up the breakdown of protein. G Davidson

19. Pepsin Activity Copy and Complete the table using the results on your sheet. G Davidson

20. Effect of pH on Enzyme Activity G Davidson

21. Model Enzymes • During an enzyme controlled reaction the substances involved – the substrates – become joined to the surface of the enzyme molecule. • The chemical reaction then occurs very quickly. • The spot on the enzyme molecule where the catalytic activity takes place is called the ACTIVE SITE. G Davidson

22. Model Enzymes • Enzyme molecules have many active sites over their surface. • Only substrates that fit the active site exactly, react on the surface of the enzyme. • Substrate molecules fit into these active sites like a key fitting into a lock. G Davidson

23. Enzyme Enzyme/substrate complex Substrate Enzyme Products Model Enzymes G Davidson

24. Model enzymes G Davidson

25. Effect of Temperature on Enzyme Activity • Because enzymes are proteins, they are affected by heat and the pH of the surrounding medium. • At temperatures above 50oC most enzymes are permanently inactivated or DENATURED. • Enzymes have a temperature at which they work best, and this is called the OPTIMUM temperature. G Davidson

26. Optimum Temperature Effect of Temperature on Enzyme Activity G Davidson

27. Investigating Urease • Urease is an enzyme which catalyses the breakdown of urea. • The activity of urease can be followed using a pH indicator to detect the presence of ammonia. • Ammonia is a strong alkali. UREASE UREA + WATER AMMONIA + CO2 G Davidson

28. Investigating Urease • Test a little ammonium hydroxide with pH paper and note the colour. • Place a little urea, water and 3 drops of indicator in a test tube. • Add a pinch of urease and note what happens. G Davidson

29. Inhibitors • Some substances are able to stop or INHIBIT the activity of an enzyme. • Repeat the urea experiment but add a few drops of silver nitrate to the test tube. • The enzyme fails to work because the silver nitrate INHIBITS it. G Davidson