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Influence of pH on the Activity of Potato Catalase.

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Introduction

Influence of pH on the Activity of Potato Catalase Catalase is found in a vide variety of plant and animal tissues, its use is to break down toxic hydrogen peroxide which is formed as a by-product of biochemical reactions, into the harmless substances, water and oxygen. The rate of activity of many enzymes is largely influenced by changes in the pH level. To show the effect of pH on the enzyme Catalase, an experiment will be conducted where potato-discs of a constant size are placed in solutions of known pH and will react with hydrogen peroxide in the solution. The rate at which oxygen is evolved will be measured using a manometer, thus reflecting the activity of the Catalase in the potato. Requirements for Experiment: - Scalpel/Sharp Cutting Device - Cork Borer - Petri Dish - Boiling Tube (with rubber bung) - Stand (with bosses and clamps) - Manometer Tube (with a select diameter 2mm/3mm) - Beaker - Syringe (5cm�) X2 - Clip - Stop Clock - Pencil - Potato Tubers - Tongs - Test Tube Rack - Hydrogen Peroxide - Citric Acid phosphate buffers, made up as shown below from Na2HPO4 (0.2 mol dm-3) and citric acid (0.1 mol dm-3) to provide 100cm3 of buffer in each case: Buffer pH Na2HPO4 cm3 Hydrogen Peroxide cm3 8.3 5 5 6.3 5 5 4.3 5 5 3.5 5 5 2.8 5 5 Before the experiment it is advised that the pHs should be checked with litmus paper or an electrical pH meter. ...read more.

Middle

4) As the reaction begins and oxygen is produced the manometer fluid should be pushed down the left hand side of the manometer tube. Using the stop clock, time how long it takes for the fluid to rise through a distance of 5cm in the right hand side of the tube. During this period gently agitate the boiling tube to ensure that the reaction is occurring at an optimal level. 5) Open the clip at the top of the boiling tube so that the manometer fluid returns to its idle position. Time the evolution of oxygen twice more and work out an average result. 6) Remove the bung and wash out the boiling tube thoroughly. 7) Repeat steps 1-6 another five times, with a fresh set of five potato discs each time and using differing buffer solutions of the chosen pH in turn. 8) For each of the final readings, divide the rate of reaction by 100 by the time taken in seconds for a 5cm rise in the right-hand manometer tube. This provides larger numbers for graph plotting. 9) Collate the results in a table 10) Plot a graph of the rate of reaction against pH for the results found. Setup: Results Table Results of the experiment are displayed as follows: pH Buffer cm3 Hydrogen Peroxide cm3 Time/Seconds 2.8 5 5 129.31 5 5 84.38 5 5 98.91 3.5 5 5 110.04 5 5 75.79 5 5 65.09 4.3 5 5 92.45 5 5 75.16 5 ...read more.

Conclusion

It therefore competes with the substrate for the active site, so the reaction is slower. A non-competitive inhibitor molecule is quite different in structure from the substrate molecule and does not fit into the active site. It binds to another part of the enzyme molecule, changing the shape of the whole enzyme, including the active site, so that it can no longer bind substrate molecules. Non-competitive inhibitors therefore simply reduce the amount of active enzyme; similar to decreasing the enzyme concentration. In conclusion, the presence of these inhibitors will have altered the reaction by increasing or decreasing the rate at which the products are produced. There will have been limitations in the results as the range of buffer solution pHs used in the experiment were inadequate to determine an exact optimal pH for the enzyme Catalase to function. To find the optimal pH, further tests could have been conducted by using pHs with closer intervals within the range of 4.5 and 6.5, where the rate of reaction increases sharply, as shown on the graph by an arrow. By analysing the results and the graphs that were produced, there are no obvious anomalies in the results achieved; however there may have been a slight discrepancy in one result which is marked on the graph/s with a circle. This could have been a consequence of any of the factors mentioned above in the evaluation section. Adam Darrah A-Level Biology 09/05/2007 Influence of pH on the Activity of Potato Catalase ...read more.

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