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  1. Practical's Enzymes

  2. Practical 1 The Breakdown of Hydrogen Peroxide

  3. ____________________ will break down into water and oxygen very slowly at room temperature Hydrogen Peroxide Introduction • ____________________ is a _________ which speeds up the breakdown of Hydrogen peroxide Oxygen Hydrogen peroxide Water Manganese dioxide catalyst • ____________ is a _________________ which speeds up the breakdown of hydrogen peroxide. Catalase is present in all living cells. Catalase Biological catalyst

  4. Aim • To show the effect of heating and catalysts on the breakdown of hydrogen peroxide

  5. Method • Set up the apparatus shown in the diagram • Water bath at 30o C Water bath at 90o C Hydrogen Peroxide + Yeast (catalase) Hydrogen Peroxide + Manganese dioxide Hydrogen Peroxide Hydrogen Peroxide A B C D

  6. Note the quantity of bubbles in each test tube • Record your observations in your results table

  7. Results No Bubbles Many bubbles Many Bubbles Few Bubbles

  8. Conclusions • Which two tubes are compared to show that high temperatures speed up the breakdown of hydrogen peroxide? • ______________________________________ • Which two tubes are compared to show that catalysts speed up the breakdown of hydrogen peroxide? • _____________________________________ Tubes A and D Tubes A and C • Which two tubes are compared to show that biological catalysts speed up the breakdown of hydrogen peroxide? • __________________________________________ Tubes A and B

  9. Evaluation • What name is give to an experimental set up which acts as a comparison • ________________________________ • Which tube is used as a comparison in this experiment • ___________________________________ A control Tube A

  10. Practical 2 The specificity of enzymes

  11. Enzyme Action • Learning objectives: • By the end of the lesson you should be able to: • Explain that enzymes are specific to their substrate. • Describe why enzymes are specific to their substrate.

  12. Introduction • Enzymes are _____________. This means that each enzyme can act on _______________________. • ______________ and _____________ are types of enzyme. Specific Only one particular substrate Catalase pepsin Egg white • __________ suspension is cloudy because it ___________________________floating in it Has large protein molecules

  13. Aim • To show that enzymes are specific to particular substrate

  14. Method • Label four test tubes A, B, C, and D and prepare as below using SEPARATE DROPPERS for each substance • Tube A-5 cm3 hydrogen peroxide solution and 1 cm3 of catalase • Tube B -5 cm3 hydrogen peroxide solution and 1 cm3 of pepsin • Tube C -5 cm3 egg white suspension and 1 cm3 of catalase • Tube D- -5 cm3 egg white suspension and 1 cm3 of pepsin

  15. Examine the contents of the tubes A and B for the presence of bubbles • Check the contents of tubes C and D to see if they are cloudy or clear • Record your results in the table • Place your tubes in the water bath at 37oC

  16. Results Bubbles • Interpretation • Which substrate is acted on by catalase? • _________________________ No bubbles Cloudy Clear Hydrogen Peroxide Which substrate is acted on by pepsin? ___________________________________ Egg White

  17. Conclusion • What do these results suggest about the specificity of enzymes? • ________________________________ Enzymes act on only one substrate , so are said to be specific

  18. Evaluation • Name 2 of the variables which are controlled to make the experiment valid? • _____________________________________ • ____________________________ Volume of substrate Volume of enzyme Temperature Time

  19. Practical 3 Enzymes and temperature

  20. Enzyme Action • Learning objectives: • By the end of the lesson you should be able to: • Describe how temperature effects enzyme activity

  21. Introduction Are made of protein • Enzymes _______________________ • If a little detergent is added to the hydrogen peroxide solution a foam is formed by the oxygen gas given off during the reaction. • The ___________________an indication of ____________ • The enzyme ______________ is found in all living tissue. It catalyses the reaction Catalase Water Hydrogen Peroxide Oxygen height of the foam gives Enzyme activity • Egg white contains protein molecules which are affected by temperature

  22. Aim: • To show the influence of temperature on enzyme activity.

  23. Method • You will be split into groups with each group carrying out the experiment at different temperatures and the results will be pooled. • 1 Label 3 test tubes A, B and C and prepare as below • Tube A - 3cm3 egg white • Tube B - 5cm3 hydrogen peroxide • Tube C - Piece of potato tissue

  24. Set up a beaker water bath (Your teacher will tell you the temperature) and place all three tubes in the water bath. You must keep the temperature constant throughout the experiment. 6 Leave for a further 10 minutes 7 Note the appearance of tube A and measure the height of the foam above the liquid in tube C. 8 Pool the results from all groups in the table. • Leave for 10 minutes • Carefully add the hydrogen peroxide to the test tube containing the potato tissue.

  25. Results

  26. Analysis of Results • Draw a line graph of results Height of foam (mm) Temperature (oC)

  27. Conclusion • What is the relationship between the enzyme activity and temperature. • As the temperature rises to ____oC enzyme activity increases. • The optimum temperature for the enzyme is ___ oC 40 Above ____oC enzyme activity decreases 40 40

  28. Evaluation • Why are the hydrogen peroxide and potato left in the water bath for ten minutes before being added together? • To allow them to reach the experimental temperature

  29. Practical 4 Enzymes and pH

  30. Enzyme Action • Learning objectives: • By the end of the lesson you should be able to: • Describe how pH effects enzyme activity

  31. Introduction • Introduction • ________ indicate the level of acidity and alkalinity of a solution • When universal indicator is added to a solution it _____________________________________ pH values Changes colour indicating the pH value Red Orange/Yellow Green Grey Blue 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acid Alkali Neutral

  32. Pepsin is an enzyme found in the human stomach which catalyses the reaction • Egg white is a ______________. It is cloudy because of the large protein molecules floating in it. Pepsin Protein Peptides Source of protein

  33. Aim • To show the influence of pH on enzyme activity

  34. Method • 1. Label three test tubes A, B, C • 2. Using separate droppers, add to each tube 3 cm3 egg white and 3 cm3 pepsin solution. • 3. Use separate droppers to now add • 4. Place the tubes in a water bath at 37oC for 20 minutes. • 1 cm3 of acid to A • 1 cm3 of water to B • 1 cm3 of alkali to C • 5. Note the appearance of each tube and then determine the pH by adding a few drops of universal indicator.

  35. Results CLEAR CLOUDY CLOUDY

  36. Conclusion • Under which pH conditions is pepsin active? • _______________________________ Acid conditions only

  37. Evaluation • How could you improve this experiment to find the optimum pH for the enzyme pepsin? (Hint: Is pepsin equally active at all pH values?) • Set up a similar experiment using a range of pH values

  38. Practical 5 Action of Phosphorylase

  39. Enzyme Action • Learning objectives: • By the end of the lesson you should be able to: • Explain that enzymes can be involved in making substances.

  40. Introduction • Phosphorylase is an enzyme found in potato tubers which catalyses the build up of starch from glucose-1-phosphate • Potato extract is liquid from the potato tuber which ________________________ phosphorylase Glucose-1-phosphate Starch Contains the enzyme but no starch • ______solution is used to ____________ Iodine Test for the presence of starch • It turns _____________ when starch is present Black

  41. Aim • To demonstrate the action of the enzyme phosphorylase

  42. Method • Your teacher will set up a dimple tile as shown in the diagram Glucose -1-phosphate = g-1-p Distilled water = DW Phosphorylase = P Column 1 Column 2 Column 3 Column 4 g-1-p P g-1-p P g-1-p P g-1-p P Row A g-1-p DW g-1-p DW g-1-p DW g-1-p DW Row B P DW P DW P DW P DW Row C Add iodine to each dimple as follows Column 1 after 5 minutes Column 2 after 10 minutes Column 3 after 15 minutes Column 4 after 20 minutes

  43. In the results, shade in the dimples which turned black after iodine was added.

  44. Results

  45. Conclusion • What is produced in row A? • ______________ • What two substances are present where this is produced? • ___________________________________ • ____________________________________ Starch The enzyme - phosphorylase The substrate - Glucose-1-phosphate

  46. Evaluation • Why is row B set up? • _____________________________________ _________________________________________ • Why is row C set up? • _____________________________________ ________________________________________ As a control to show that glucose-1-phosphate can not produce starch on its own As a control to show that phosphorylase can not produce starch on its own