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Investigate how changing the concentration of hydrogen peroxide (substrate) affects the rate of reaction of the enzyme Catalase.

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Introduction

Biology Coursework Introduction: Catalase, like all enzymes, is made up of protein molecules. It can be found in the cytoplasm of living tissue. It speeds up the decomposition of Hydrogen Peroxide, a metabolic waste product, into water and oxygen that can safely be removed from the cell. The type of reaction involved is known as a catabolic reaction (i.e. substrate broken down.)This is simply because the substrate enters the active site and is broken down, and leaves as 2 separate products, in this case water and oxygen: 2H2O2 > 2H20 + O2 Like all enzymes, the rate at which the enzyme works is affected by many variables. These are: 1. Temperature: As increase in temperature and therefore heat energy reaching the enzymes and substrate molecules causes them to increase random movement. The more heat energy the more the molecules move and so collide more often. The more collisions between molecules the greater chance there is that the substrates will fit into the active site. Therefore there is an increase in rate of reaction. However if the temperature continues to increase above the optimum temperature of the enzyme (what it works best at) the polypeptide bonds that are responsible for the specific shape of the active site, start to break. This means that the specific shape of the active site starts to distort. The active sight can become permanently damaged and at this point the enzyme is said to be denatured. The substrates will no loner fit into the active sights and so a reaction does not take place. 2. PH Value: Enzymes also have an optimum PH value at which they work best. If the PH value of the medium is changed it can have the same affect as a temperature change. The polypeptide bonds start to break and the shape of the active sight begins to distort meaning the substrate will no longer fit. ...read more.

Middle

o Inhibition: I will be adding nitrate to the hydrogen peroxide in the same way as with the water. This nitrate solution may be either no inhibitor, competitive or non-competitive inhibitor. Throughout the rest of the experiment this variable will remain unchanged. Prediction: In my experiment I will be studying how the varying concentrations of Hydrogen Peroxide affects the rate of reaction/amount of oxygen given off. I will also study how the varying concentrations of nitrate solution affect the rate of reaction/amount of oxygen given off. I can then compare the 2 sets of results. From my background knowledge gained from my A-S Course can make some predictions on what I think will happen. I think that when I add water to the hydrogen peroxide, therefore decreases the concentration the rate of reaction will fall quite a bit in comparison to when there is 100% concentration. As the concentration of hydrogen peroxide increases, the rate of reaction will also increase at a corresponding rate. This is because there are less substrate molecules to react with the enzyme and therefore less oxygen will be given off. I also think that as the concentration increases the rate at which the rate of reaction increases will decrease. This is because all of the enzyme molecules are in use and it is the enzyme concentration that is the limiting factor, not the substrate concentration. When I use nitrate solution to vary the hydrogen concentration instead of water, one of two things could happen. If the nitrate is an inhibitor, the rate of reaction/amount of oxygen given off will decrease more dramatically as more nitrate is added compared to when water is added to the hydrogen to dilute the solution. This is because not only is the hydrogen peroxide becoming more dilute, but also an inhibitor is replacing it. Therefore the inhibitor will spend time in the active site instead of the substrate and slow down the reaction (see above). ...read more.

Conclusion

* I could have crushed and then drained the celery, so that I could use just the juices of the celery as a source of enzyme. This would have been more accurate than simply using blocks of celery because the solution could have been mixed up, and therefore the concentration of enzyme used it each experiment would have been the same. It would have been even more accurate to use a known molar solution as a source of enzyme. * To minimise the errors of the timing between placing the bung over the end of the boiling tube to start collecting the oxygen and starting the timer could have been minimised by 2 people doing the experiment. That way one person could have placed the celery in the text tube, the other could have put the bung on the end of the test tube, and the first person starts the timer. * I could have also, if more time was available taking readings using a larger measuring cylinder, for a longer time, to see what the maximum velocity was, and whether the experiment using the nitrate solution would have reached it. I believe the fact that I did not get results for all the concentrations going up in 10%'s, has not affected my overall conclusion. But I do believe that because I did not know what the maximum velocity was-this has affected my overall conclusion. If I knew what the maximum velocity was I could have made more accurate decisions on what the nitrate solution was. If I had tested using the hydrogen peroxide, and added 3g of celery; using a larger measuring cylinder to find the Vmax, I could have done the same with the experiments using the nitrate solution. If they had reached Vmax, but taken longer to do so, I could then be definite that the nitrate solution was a competitive one. But if they did not reach Vmax, then I would have known that it was a non-competitive one. This can be shown in the earlier drawn graph of predicted results. o ?? ?? ?? ?? Page 1 ...read more.

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