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Investigating a factor affecting the rate of breakdown of sucrose into glucose by the enzyme sucrase (invertase).

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Introduction

GCSE Biology Coursework-Enzymes Tom Doke Summer '03 Plan Introduction I shall be investigating a factor affecting the rate of breakdown of sucrose into glucose by the enzyme sucrase (invertase). In order to do this successfully it will be necessary to ensure that all other limiting variables remain constant throughout the reaction. I shall be using clinistix to determine when the reaction has taken place, as they turn from pink to blue in the presence of glucose. Background Information The enzyme sucrase is as a biological catalyst, speeding up the rate of reaction, without taking part in it. Only Sucrose can fit into Sucrase's unique active site, forming an enzyme substrate complex. This is called the lock and key mechanism and is shown below: There are a number of variables, which may affect the experiment. I shall choose the one I think shall be easiest to vary, and give the most representative results, whilst keeping the others constant: Temperature- As the temperature of the active site increases, the enzyme and substrate particles gain kinetic energy (Kinetic theory of matter), moving quicker, and thus colliding more frequently. This causes the rate of reaction to increase up until a certain point. This is called the optimum temperature, and for enzymes is around 40oC. Beyond this point the weak bonds in enzymes are broken, and so their chemical and physical properties change. ...read more.

Middle

This will allow me to draw conclusions more effectively. Analysis Results table: Temp. 500 (oC) Repeat 1 Repeat 2 Repeat 3 Mean Mean Time 20 78 87 82 82.3 6.1 30 46 38 43 42.3 11.8 38 24 19 22 21.7 23.1 40 17 16 19 17.3 28.8 42 17 15 15 15.7 31.9 50 42 43 48 44.3 11.3 60 300(no change) 300(no change) 300(no change) 300(no change) - My results and graph show that the rate of reaction increases as temperature is increased. This is true until 42oC, the optimum temperature, of the enzyme sucrase, according to my results. After this point the rate decreases. I have concluded that the experiment can be explained scientifically, as below: By the lock and key mechanism an enzyme and substrate fit into each other. As the temperature of the active site increases, the sucrase (enzyme) and sucrose (substrate) particles gain kinetic energy (Kinetic theory of matter), moving quicker, and thus colliding more frequently. This causes the rate of reaction to increase up until a certain point. This is called the optimum temperature, and for enzymes is normally around 40oC. However in my results the optimum temperature appears to be 42oC. This could be due to the enzyme sucrase having been extracted from a plant as opposed to an animal. ...read more.

Conclusion

every 5oC instead of every 10oC. Thus, by plotting more points, I would have been able to be more certain about the shape of the results graph. Unfortunately on the day there was no buffer available, which in a future experiment would be useful, along with Universal Indicator paper, to control and monitor pH. As I have said in my plan, pH affects enzyme activity in a similar way to temperature. I would like to do some further work to back up my conclusion. This could involve times being taken for different concentrations of sucrose solution by mixing various volumes of 10% sucrose and distilled water. I would expect at graph like the one below to be produced. Up until the point marked by the line 'a' direct proportionality exists, because by increasing sucrose concentration rate increases too. However after this point increasing concentration has no effect on rate, as concentration of sucrose is no longer the limiting factor. All the active sites in the sucrase are occupied by sucrose molecules, and thus to further increase rate, a greater sucrase concentration is needed. This further experiment would help me to better understand the nature of the reagents sucrose and sucrase, and ensure that temperature is the limiting variable in the experiment I performed. As my results agree with the prediction, which was based on good scientific knowledge and understanding, I think the experiment was a success. GCSE Biology Enzyme Coursework Tom Doke Merchant Taylors' School ...read more.

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