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Investigation into the rate of reaction of the enzyme catalase in yeast when decomposing hydrogen peroxide.

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Introduction

Investigation into the rate of reaction of the enzyme catalase in yeast when decomposing hydrogen peroxide. Aim To investigate the rate of reaction of catalase when reacted with hydrogen peroxide. The enzyme catalase converts hydrogen peroxide, a by-product of cellular reactions, into water and oxygen for use in other reactions in the formula below; 2H2O2 ?2H2O + O2 Background Knowledge Enzymes have a specific area where they work on the substrate. Enzymes have a specifically "folded" protein location called the active site, where the enzyme-substrate reaction takes place. Enzymes speed up chemical reactions by forming enzyme-substrate complexes and, in this case, releasing hydrogen and water, harmless chemicals instead of poisonous hydrogen peroxide inside living cells. This type of reaction is called an anabolic reaction, where chemicals are split up into smaller particles. The rate of reaction depends on a number of factors, including the optimum temperature and pH (which depends on where they would naturally be occuring in the body) and the ratio of enzyme to substrate as the active site on an enzyme can only work on one substrate at a time. Prediction I think that as I increase the substrate concentration(hydrogen peroxide) the amount of oxygen evolved in a certain time period will increase. The rate steadily increases when a higher concentration substrate is added because more of the active sites of the enzyme, catalase in yeast, are being used which results in more reactions according to kinetic theory so the amount of oxygen released in a given time is higher. ...read more.

Middle

Water (ml) % H2O2 5 20 20% 10 15 40% 13 13 50% 15 10 60% 20 5 80% 25 0 100% This will create 6 different concentrations for reactions with yeast. Add known amount of yeast powder to clean test tube and add known volume of water as buffer for pH. This gets clamped as shown in diagram. When ready with stopwatch, add one of the concentrations of H2O2 and take regular readings as to the amount of O2 evolved, i.e every 30s for 3 minutes. Repeat with same concentration of H2O2 and record results. Repeat with new concentration. Trial To find out what amount of enzyme and volume of substrate to use, I had to do a trial. This involved changing the variables and testing to see if it reacted too much or too little. 1st Trial I tried using 2 spatulas of yeast powder, with 5 mls of water as a buffer, and 5 mls of neat H2O2 (20 vols). This caused a vigorous reaction which had the "bubbles" of O2 travelling down the delivery tube and interfering with the amount of O2 evolved. As my variable was the concentration of the H2O2, I thought it would be better to reduce the mass of yeast powder that got added and set a level for the independent variables to use for all the experiments. 2nd Trial Next, I tried only 1 spatula of yeast powder and te rest of the above amounts the same to see if this controlled the reaction to an accurate level. ...read more.

Conclusion

The pattern shown on the graph was made by 6 different concentrations of hydrogen peroxide which gave a good enough range to show clearly what I intended. As can be seen on the graph, there is a slight plateau between 40% and 60% vol of H2O2 and also the gradient at the start of the graph is lower than on the final concentration. This could be because the amount of enzymes in the yeast can vary from sample to sample, therefore possibly reducing the number of active sites available for the substrate. It could also be that at that concentration the number of substrate molecules increases and the enzyme can only split one substrate at once so the oxygen evolved slows down. The only way to see if this is an anomaly is to test more of the yeast at that concentration. But there are no distinct anomalies on the results that I have. This helps to prove the prediction more strongly. Suggestions for improvement Make the measurement of H2O2 and the water amounts in the different concentrations more accurate by using a volumetric pipette and smaller measuring cylinders. Then the numbers of concentrations can be increased as they are more accurate and a smoother curve should be shown on the graph with a steadier gradient. Make some concentrations of H2O2 above 20 vol, (100%) to show what happens when there is an excess of substrate to enzyme. This would, once again, make the graph more accurate as the plateau would be clear. Francesca Spencer 13JC 02/05/07 Page 1 of 5 ...read more.

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