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Enzyme catalysed decomposition of hydrogen peroxide

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Objective The purpose of my experiment is to determine the effect of different concentration of copper Hydrogen Peroxide on the activity of catalase and the production of oxygen. Background Knowledge Catalase is an enzyme which is globular protein - the secondary protein structure is folded into a spherical or globular shape. Hydrogen bonds, ionic bonds, disulphide bridges and hydrophobic interactions (between groups of amino acids) maintain the specific three dimensional shape of the enzyme. This specific 3D shape is very essential for the functioning of enzymes. The part of the enzyme which binds with the substrate is called the active site. The shape of the active site differs from one enzyme to another. This makes the enzyme react only with a specific substrate, which fits the active site. Enzymes also lower the activation energy and provide an alternate (lower energy) pathway for the reaction to proceed. Thus the rate of reaction speeds up (catalyst). Figure 1 The enzyme active site binds to hydrogen peroxide (substrate) and decomposes it to oxygen and water. Catalase (Yeast) Hydrogen Peroxide Water + Oxygen 2H2O2 2H2O + O2 Figure 2 There are many factors which affect the activity of enzymes; the concentration inhibitor is one of the factors which have a massive effect the activity of enzyme. An enzyme inhibitor is a substance that slows down the rate at which an enzyme-catalysed reaction takes place. Many enzyme inhibitors work by binding with the enzyme, with the result that the enzyme can no longer bind with its substrate Some inhibitors have shapes rather like the enzyme's normal substrate molecule, allowing them to bind at the active site of the enzyme. They are called active site-directed inhibitors. Figure 3 If there is an inhibitor molecule in the active site, the substrate cannot bind there. Some active site-directed inhibitors bind permanently to the active site, so that they permanently inactivate the enzyme. ...read more.


Buffer solution (pH 7) It is put in a test tube and acclimatised before mixing it with the potato tubes and the other solutions It is used to maintain the pH of the reaction constant at 7 throughout, which is the optimum pH for the reaction involving catalase. Hydrogen peroxide solution 20% It is put in a test tube and acclimatised before making it react with catalase. The concentration of the Hydrogen Peroxide was 20% It functions as the substrate in the catalysis reaction. I decided to study catalase, and since enzymes are specific, Hydrogen Peroxide is the only substrate that can fit into catalase's active sites. Stopwatch To measure the length of time of the reaction, and also to measure the length of time of the acclimatisation process undergone by the 3 test tubes containing the reactants, and the beaker which functions as the environment in which the reaction is happening. The accuracy of the stopwatch was to half a second. For measuring the total time for the experiment (120seconds) and the time intervals in which the amount of oxygen produced would be measured. (20 seconds). The test tubes containing the reactants are inserted into the water bath set at 35 C, so that the solutions temperature rises to the one in the water bath, the same is carried out with the beaker. This process has to be undergone for a specific length of time, measured by the stopwatch. Graduated syringe x2 10 ml One is for injecting the Hydrogen Peroxide into the test tube at the start of the reaction; the other one is used to mix right amounts of other solutions. To make sure that the hydrogen peroxide doesn't make contact with the other reactants before the right apparatus is set up for the counting of the gas produced. The other syringe is used to measure for example, the amount of distilled water to inject into the copper sulphate solutions. ...read more.


Limitation of experimental techniques and uncertainties associated with the equipment: First I will calculate the uncertainties associated with the measurements that I have taken. I will choose the lowest value where I have a choice to illustrate the 'worst case scenario' Measuring cylinder: The uncertainty associated with the measuring cylinder reading is 0.5cm3 The % uncertainty in a measuring cylinder reading of 50cm3 = 0.5 � 100 =1.0% 50 Percentage error = 1.0% Thermometer: The thermometer I used in this experiment is accurate to 0.5 oC The uncertainty associated with the thermometer reading is 0.5oC The % uncertainty in a thermometer reading 40oC = 0.5 � 100 = 1.25% 40 Percentage error = 1.25% Gas syringe: The gas syringe I used in this experiment is accurate to 0.5 cm3 The uncertainty associated with the gas syringe reading is 0.5cm3 The % uncertainty in a gas syringe reading of 100cm3 0.5 � 100 = 0.5% 100 Percentage error = 1.25% I have listed some of the limitations of the experimental techniques in the following table Aspect of procedure Limitation Effect on the overall result Reading on Graduated syringe The syringe was graduated to the nearest 0.5ml The overall effect is very Insignificant because it was unlikely to be a possible error when measuring 10 ml of Hydrogen Peroxide, yeast solutions or the other solutions (copper sulphate & buffer solution) using 10ml Graduated syringe Making recordings at identical intervals(every 10 seconds) The difficulty was that it was difficult to read off values exactly on time when the reaction was still taking place. Reading on gas syringe The syringe was graduated to the nearest 0.5ml Improvement: If I was given a chance to conduct another similar experiment, I would change some of the apparatus, improve the procedures and techniques that were during the experiment. My experiment could be improved in numerous ways. Further investigation This experiment can be extended to investigate the type of inhibitor that was used through out the experiment i.e. (Competitive or Non- competitive inhibitor) ?? ?? ?? ?? Enzyme catalysed decomposition of hydrogen peroxide Yeshak Dejene - 1 - ...read more.

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