The Hydrogen Peroxide Breakdown

1 The Hydrogen Peroxide Breakdown 7. The Hydrogen Peroxide Breakdown Examining Factors that Affect the Reaction Rate of Enzymes Using a Graphing Calculator and Data Collection Device There are thousands of chemical reactions that occur in an organism that make life possible. Most of these chemical reactions proceed too slowly to occur by themselves. Enzymes are protein catalysts that speed up chemical reactions in a cell. Catalysts are not changed by the reactions they control, and are not used up during the reaction. Enzymes, therefore, can be used over and over again. Enzymes are large complex proteins made by the cell and allow chemical reactions to take place at the temperature of the cell.

2 These catalysts are needed in only very small amounts because a single enzyme molecule can complete the same reaction thousands of times in one minute. Each enzyme is very specific and can only catalyze a certain reaction. The specific reaction catalyzed by an enzyme depends on the molecular structure and shape of a small area of the enzyme's surface called the active site. The active site can attract and hold only its specific molecules. The target molecule that the enzyme attracts and acts upon is called the substrate. The substrate and the active site of the molecule must fit together very closely. Sometimes the enzyme changes its shape slightly to bring about the necessary fit.

3 A chemical reaction requires that bonds in the reactants be broken. The initial energy that must be absorbed in order to break the bonds of the reactant molecule is called the energy of activation. Laying the Foundation in Biology 329. 7 The Hydrogen Peroxide Breakdown Enzymes work by lowering the energy of activation. For example, Hydrogen Peroxide decomposes to form water, H2O, and oxygen gas, O2. While this is a catabolic reaction, the rate at which it occurs is slow. Light and temperature affect the reaction rate. As a result, bottles of Hydrogen Peroxide you may purchase at the drug store are sold in light-blocking brown bottles and have instructions to store them in a cool dark place.

4 Hydrogen Peroxide also comes with an expiration date because even with cool and dark storage, the Breakdown of H2O2 molecules will still occur to some degree. Hydrogen Peroxide is toxic to cells. This property makes it useful for treating open wounds since it kills invading bacterial cells. Interestingly enough, Hydrogen Peroxide is a by-product of some biochemical pathways found in many cells. Yet, the accumulation of Hydrogen Peroxide can kill a cell. Cells, therefore, cannot wait for Hydrogen Peroxide to naturally decompose because that takes too much time. Most tissues produce the enzyme, catalase, to increase the rate of Hydrogen Peroxide 's decomposition. Catalase lowers the energy of activation needed for the decomposition and as a result, more molecules are able to be decomposed in a shorter amount of time.

5 There are factors that can affect how fast an enzymatic reaction occurs. For example, an increase in the amount of enzyme will increase the reaction rate. There are more enzyme molecules available to be involved in the reaction. Another factor that can affect how fast the enzyme works is temperature. An increase in temperature causes the molecules to move faster and engage more frequently in a chemical reaction. At higher temperatures though, the enzymes will denature as the Hydrogen bonding falls apart. This lab investigates the effect of enzyme concentration and temperature on an enzymatic reaction. The reaction used in this laboratory exercise is the decomposition of Hydrogen Peroxide and the enzyme used is catalase.

6 A pressure probe connected to an interface device and graphing calculator will measure the amount of oxygen gas produced. The more oxygen gas produced the greater the increase in pressure. PURPOSE. The purpose of this laboratory exercise is to determine the reaction rate of the decomposition of Hydrogen Peroxide when the concentration of catalase is varies or the temperature is varied. 330 Laying the Foundation in Biology 7. The Hydrogen Peroxide Breakdown MATERIALS. pressure sensor probe graphing calculator CBL or LabPro interface filter paper disks 3% Hydrogen Peroxide solution catalase solution forceps test tube rack 10 mL pipette 10 mL graduated cylinder 2 ea 50 mL beakers 80 mL test tube # 4 test tube stopper with eye dropper link cord Safety Alert CAUTION: Take care not to spill any liquids on the interface or graphing calculator.

7 PROCEDURE. Note: You will either do Part I or Part II of this experiment and then share your results with another group. PART I (EFFECT OF CONCENTRATION). 1. Answer the pre-lab questions on the student answer page. 2. Formulate two hypotheses: The first hypothesis should be about the effect of enzyme concentration on the reaction rate, and the second hypothesis should be about the effect of temperature on the enzyme reaction rate. Record this on the student answer page. 3. Slide the calculator and CBL or LabPro Interface in the bottom part of the cradle and it will click into place. Snap the calculator into the top portion of the cradle. 4. Plug the short black link cable into the link port on the bottom of the TI Graphing Calculator and the interface.

8 5. Plug the gas pressure probe into channel 1 of the interface. There should piece of plastic tubing from the pressure probe. Some versions of certain pressure probes have valves for opening and closing the sensor. If the pressure probe has such a valve, ensure that it is open in accordance to the directions accompanying the probe. 6. Turn on the calculator and press for a TI 83+ or for the TI 83 then press the number key that precedes the DATAMATE program. At this time the interface should have automatically identified your pressure sensor. It will display the correct pressure in the upper right hand corner. If the correct pressure is not displayed do the following: Select SETUP from the MENU by pressing.

9 Select CH1 from the MENU and press . Laying the Foundation in Biology 331. 7 The Hydrogen Peroxide Breakdown Press for more, press again for pressure. Select the correct type of probe. Select MMHG by pressing Press to indicate OK. 7. Select SETUP from the MENU by pressing . Select MODE by pressing the and then . Select "TIME GRAPH" by pressing and then again to change the time settings Enter 3 as the time between sample, in seconds, press . Enter 99 as the number of sample (the interface will collect data for approximately five minutes), press . 8. Another window will appear with the summary of the probes and the length of the experiment. Press to indicate OK. Press or OK again to return to the main menu.

10 9. A new window will appear and the calculator is now ready to start the experiment. DO NOT press until you are ready to run the experiment. 10. Place the other end of the aquarium tubing found on the pressure probe onto the eye dropper sticking out of the #4 test tube stopper. 11. Place the test tube in a test tube rack. Measure 10 mL of Hydrogen Peroxide with a graduated cylinder and add it to the test tube. 12. Pour a small amount of the catalase solution into the 50 mL beaker. Keep the catalase beaker on ice. 332 Laying the Foundation in Biology 7. The Hydrogen Peroxide Breakdown 13. Obtain some paper filter disks and separate any paper disks that may be stuck together. Using the forceps, dip one disk into the catalase solution.