Chapter 10

1. Chapter 10

2. Objectives for today’s lesson • Introduction to Metabolism • Review of Anabolic and Catabolic reactions • Define Enzymes and look at their structure • Outline the role of enzymes as catalysts • Outline the role of substrates

3. Metabolism(all of the chemical reactions in a living thing) Anabolic reactions Catabolic reactions Small molecules arecombined to make larger molecules. Energyis needed Large molecules arebroken downinto smaller molecules.Energyis given out.

4. Sources of energy in cells for anabolic reactions • Solar energy Sunlight is a source of energy capable of being absorbed by cellular pigments e.g. chlorophyll. 2. Cellular energy Catabolic reactions in cells release energy

5. Enzymes • Enzymes are molecules made of protein • They have a globular, 3 dimensional shape

6. Enzyme Structure

7. Enzyme substrate reaction

8. Enzyme substrate reaction

9. Enzymes

10. Enzymes – the key to it all Almost all chemical reactions that take place inside living things are controlled by enzymes. Enzymes are biological catalysts – they change the rate of reactions without getting used up themselves. Every enzyme is a protein and has a specific 3D shape. Enzymes are proteins that speed up a reaction without being used up in the reaction

11. Catalysts A catalyst is a substance that speeds up a reaction without itself being used up in the reaction. Enzymes are catalysts made of protein. Enzymes are called biological catalysts.

12. Enzyme structure

13. Enzyme Action The substrate is the substance with which an enzyme reacts e.g. Starch is the substrate for Salivary Amylase The product(s) is the substance(s) the enzyme forms after a reaction. E.g. Maltose is formed from the reaction between salivary amylase and starch.

14. Enzymes • Made of protein • Enzymes have the correct shape to fit one type of substrate • Enzyme reactions are reversible (they can proceed in either direction) e.g. X ----- Y + Z Or X -------- Y + Z

15. Enzymes • Enzymes are named by adding the ending ASE to the name of their substrate.

16. Role of Enzymes Enzymes are necessary in plants and animals to control metabolic reactions. Catabolic enzymes Anabolic enzymes

17. Catabolic enzyme Catalyse is an enzyme that converts hydrogen peroxide into water and oxygen • Catabolic = breaks a big molecule into smaller ones

18. Anabolic Enzyme DNA Polymerase is an enzyme that builds DNA nucleotides from tiny nucleotide units in our cells Anabolic = makes small molecules into bigger ones

19. Consider This • Amylase is an enzyme found in saliva. It breaks starch molecules into smaller maltose molecules • What is the substrate? • What is the product? • Will amylase break fats into fatty acids + glycerol? Why? • Is this an example of a catabolic or an anabolic reaction? Why?

20. And This • DNA Polymerase is an enzyme that builds DNA using tiny molecules in our cells • What is the substrate? • What is the product? • Do you think DNA polymerase could do the reverse reaction? Why?

22. Learning Check • What is meant by a substrate? • What is the unit formed when an enzyme combines with its substrate called? • Give an example of an anabolic reaction • Give an example of a catabolic reaction

23. Factors affecting enzyme activity • Temperature – As the temperature increases from 0oC the rate of molecular movement increases and the substrate molecules and enzymes to bump into each other more often and the rate of reaction increases.

24. Denatured Enzyme A denatured enzyme has lost its shape and can no longer carry out its function. Enzymes can be denatured by a range of factors including: Unsuitable pH, inhibitors, radiation, high temperatures etc.

25. pH

26. pH scale runs from 0 to 14 • Enzymes work over a very narrow pH range • Outside their pH range enzymes lose their shape (become denatured) very quickly • Optimum (best) pH for most enzymes is 7

27. Enzymes and Temperature

28. Mandatory experiment Investigation 1 • How does temperature effect the rate of reaction of an enzyme?

29. Step A • 5g of chopped up celery • 1 drop of washing up liquid • 10mls of Buffer solution ALL INTO A GRADUATED CYLINDER

30. 5ml of Hydorgen peroxide • The graduated cylinder and contents • ALL IN A WATER BATH UNTILL THEY ARE THE SAME TEMPERATURE AS THE WATER BATH Step B

31. Step C Add the hydrogen peroxide to the graduated cylinder.Time for 1 minute and see the volume of oxygen made

32. Temperature and enzymes • At very low temperatures molecules are moving slowly and enzymes work slower because of less collisions with substrate • As temperature increases molecules start to move and bump into each other causing the rate of reaction to increase

33. Rate of reaction 37 Temp (oC) Temperature and enzymes • Above certain temperatures enzymes start to lose their shape the rate of reaction falls. • When the shape is fully lost the enzyme is said to be denatured this is usually a permanent condition • Human enzymes work best at body temperature (37°C) • Plant Enzymes work best at 20-30 °C

34. Check your learning • Why does temperature have an effect on the rate of reaction? • Why do enzymes not work well at low temperatures? • As temperature increases what happens to enzyme activity? • What is the optimum temp for enzymes in plants and humans? • What happens when an enzyme loses its shape?

35. Enzymes and pH

36. Mandatoryexperiment • Investigation 2 - To investigate the effect of pH on the rate of enzyme action

37. pH • pH scale goes from 0 -14 • Less than 7 is acidic • 7 is neutral • More than 7 is basic (or alkaline)

38. To investigate the effect of pH on catalase activity

39. Finely chop the celery. Weigh 5 g of the chopped celery. Step 1

40. Step 2 Add 10 ml of your pH buffer 4, one drop of washing-up liquid and 5 g of celery into a graduated cylinder.

41. Step 3 Add 5 ml of hydrogen peroxide to a boiling tube.

42. Step 4 Place the graduated cylinder and the boiling tube in a water bath at 25 °C – until they reach the required temperature

43. Step 5 Add the hydrogen peroxide into the graduated cylinder and record the volume immediately.

44. Step 6 Time for 2 minutes and record the final volume.

45. Rate of reaction 0 pH 14 Enzymes and pH • pH is important for enzymes as it can make enzymes change their shape! • The best ph (optimum pH) is usually pH 7 • Outside this they lose their shape and get denatured

47. Check your learning.. • What is an enzyme? Why are they needed for our metabolism? • What does rate of reaction of an enzyme mean? • What does an enzyme act on? • What effect does temperature have on the rate of activity of an enzyme? • What effect does pH have on the rate of activity of an enzyme?

48. Higher level – The active site theory of enzymes

49. How enzymes work Enzymes are not flat they have a 3D structure The active site is the specific part of the enzyme which combines with the substrate.

50. Enzymes – active site theory Because of the special shape of the active site enzymes are very specific about the reactions they catalyse. If the shape of the active site changes then the enzyme cannot work and is denatured.