Kinetic theory - Sample Essay

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 (5cmi?? ) 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:

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Buffer pH Na2HPO4 cm3 Hydrogen Peroxide cm3 8 Before the experiment it is advised that the pHs should be checked with litmus paper or an electrical pH meter. Safety: Due to the corrosive nature of Hydrogen Peroxide, safety glasses and lab coats will be worn in the event that any chemical is spilled. As an extra precaution the equipment will be placed as far into the work surface as possible to prevent any equipment from falling. Variables: As temperature increases, molecules involved in the reaction will move faster (kinetic theory).

In an enzyme catalysed reaction, such as the experiment to be conducted, higher temperature will increase the rate at which the enzyme and substrate molecules form a complex, therefore, increasing the rate at which the products are formed. As the temperature continues to rise the hydrogen and ionic bonds that structurally hold the enzyme in its shape, are broken. When the structure is disrupted, the enzyme will become denatured as the active site has permanently changed shape and substrates will not bind with the enzyme, rendering it useless.

In order to control this variable, the temperature will be maintained at a constant level of 23 degrees centigrade (room temperature) for the enzyme to function effectively. A test tube rack and tongs will be used to hold the apparatus to prevent the equipment from conducting heat from my hands. When there is an excess of enzyme molecules, an increase in the substrate concentration will result in an increase in the rate of reaction. To control the substrate (hydrogen peroxide) concentration the same quantities of substrate will be used for each test, 5ml syringes will accurately measure the amount required.

When excess substrate is present, an increase in enzyme concentration will result in an increase in the rate of reaction. However, where the substrate is a limiting factor in the reaction an increase in enzyme concentration will have no effect on the rate of reaction. To keep the enzyme concentration at a constant level, the potato discs will be cut to the same measurements and each will be weighed to ensure a similar mass before they are used in the experiment. By keeping the variables constant a fair test should be conducted, resulting in accurate, useful results.



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