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Name: ____________________ ENZYME FUNCTION LAB 9 PURPOSE To explore the role of enzymes in chemical reactions. INTRODUCTION Enzymes are some of the most important kinds of molecules found in living cells. Cells could not function without enzymes. They control the chemical reactions of the cells. To understand how enzymes work, you will be observing some simple chemical reactions with hydrogen peroxide. you may have hydrogen peroxide in your medicine cabinet at home. It is commonly used as a bleaching and disinfecting agent. Hydrogen peroxide has the chemical formula H2O2. Notice the similarity between this formula and the formula for water, H2O. Hydrogen peroxide is an unstable compound, which turns into water by the following reaction: 2H2O2 ─────────────> 2H2O + Hydrogen peroxide Water O2 Oxygen Hydrogen peroxide is stored in a brown bottle to deep out light, which speeds up this reaction. Certain chemicals can also dramatically increase the speed at which this reaction takes place. In this lab you will work with some of them. Caution: Be careful not to get the hydrogen peroxide on your skin or your clothes. It is powerful bleach. Enzymes are proteins that speed up chemical reactions because they have a three-dimensional shape that accommodates their substrate(s), the reactant(s) in the reaction. This shape, therefore, determines the specificity of the enzyme and is important to the action of the enzyme. Various factors such as pH and temperature can denature enzymes and cause them to lose their effectiveness. Today's laboratory experiments will test the action of enzymes and the factors that affect their activity. CATALASE Catalase is an enzyme present in cells that speeds up the breakdown of hydrogen peroxide, a toxic chemical, to water and oxygen: 2H2O2 ────────────> 2H2O & + O2 Hydrogen peroxide water Oxygen As the reaction occurs, effervescence develops that is easily observable. 27 For the experiments below, record your results in the following manner: Results Record No effervescence 0 Moderate effervescence + Good effervescence ++ Very good effervescence +++ MATERIALS LIVER OR POTATO 3 TEST TUBES TEST TUBE RACK MORTAR AND PESTAL EYE DROPPER PROCEDURE HYDROGEN PEROXIDE HYDROCHLORIC ACID SODIUM HYDROXIDE SAND A: : Surface area on Enzyme Activity: Label and mark off three test tubes at 4 cm. Fill each to the mark with H 2O2. To the first tube, add a pinch of sand; to the second, add a 1 cm piece of fresh liver or potato and to the third, a macerated cube of liver/potato. To macerate the liver/potato take a 1 cm piece, place in a mortar, and grind with a pestle; pour off the contents into the tube of H2O2. Record and explain your results. Tube Contents Results Explanation 1 2 3 B: Effect of pH on Enzyme Activity Label and mark off three test tubes at 2 cm and 7 cm. Fill as follows: Tube 1 Add water to the first mark and one cube of macerated Tissue. Wait 3 minutes. Add H2O2 to the second mark. Record your results in the chart provided. Tube 2 Add HCL to the first mark. Add one cube of macerated Tissue. Wait 3 minutes. AFTER WAITING, add H2O2 to second mark. Record your results. Tube 3 28 Add NaOH to the first mark. Add one cube of macerated Tissue. Wait 3 minutes. AFTER WAITING, add H2O2 to the second mark. Record your results. CAUTION: HCL is a strong caustic acid and NaOH is a strong base. Exercise care in using these chemicals and follow the instructions of your instructor as to the disposal of these tubes. If any acid or base should spill on your skin rinse immediately with clear water. Tube Contents Results Explanation 1 2 3 C: The Effect of Temperature Design an experiment to test if heating destroys the enzyme catalase. procedure and observation. Point form is acceptable. Describe fully your ANALYSIS What two products does hydrogen peroxide change into when it breaks down? What effect does a catalyst have on this chemical reaction? What do you think causes the bubbling in this reaction? What is the function of an enzyme? What enzyme acts on hydrogen peroxide in living organisms? Would this enzyme act on chemicals other than hydrogen peroxide? Why or why not? 29 30