The effect of temperature on the rate of an enzyme catalysed reaction

H2O2 is a good substrate to use because we know exactly how much oxygen gas should be produced. We should use Hydrogen Peroxide from the same batch so that it will decompose the same amount. It should be stored in cool conditions to minimise decomposition. We are investigating the effect of changing temperature on a reaction. If this is to be a fair test with reliable useful results obtained other variable factors need to be controlled. Enzyme controlled reactions are very sensitive to many factors and are easily affected. We want to keep these other factors constant throughout our tests whist we only vary temperature so we can see what affect changing this factor alone. We have chosen to use potato in our experiment because the catalase enzyme is present in potato and we can also easily control the surface area and quantity of potato, which is important.

When temperature is increased the increased heat energy raises the kinetic energy of the reacting molecules leading to more frequent collisions between substrate and enzyme. More enzyme substrate complexes are formed per second, with a corresponding increase in the rate of catalysis and on the number of product molecules. Therefore the temperature of the environment surrounding the system should be kept constant and the temperatures variables should be accurate.

We already know that concentration affects enzyme activity as when concentration is increased there are more active sites available for reaction so collisions occur more frequently between substrate and enzyme, so there are more substrate complexes which form per second- so the rate of reaction increases. If enzyme concentration is varied then this will affect the rate of reaction. Can attempt to control this by using the same potato for each experiment. Surface are should be kept constant. If the piece of potato is for example cut into smaller pieces whilst another is left in a larger piece it will have a greater surface area If the potato has a larger surface area then there will be a much larger area upon which the collisions between substrate and enzymes occur. More enzyme substrate complexes will form per second and the rate of reaction will increase. To control surface area we need to use a potato borer to keep surface are constant throughout. It is also important that we use the same potato for each experiment as different potatoes could have different concentrations of enzymes within them and the y could also be of different ages, which could affect the rate of reaction

These are all the variables that I feel need to be controlled within the experiment so that the rate of reaction is not affected by anything other than temperature. However I also need to record my results at regular intervals so I can fairly compare the rates of reactions between different temperatures. I will take the readings of the volumes of oxygen produced every 20 seconds from immediately after the Hydrogen Peroxide has been added to the conical flask containing the potato. It is important that results are obtained at the same frequency so that we can see how oxygen evolution occurs across the whole experiment.

Method

The apparatus will be set up as shown in the diagram below-

* Use a size 5-potato borer to extract a length of potato. Cut this equally into 10 pieces of length 5mm. Put these pieces into a conical flask. Dispose of the excess.

* Pour around 25cm3 of Hydrogen Peroxide into the 50 ml beaker.

* Pour water into both 250ml beakers and cool them to 10 oC. Check with a thermometer. Put the conical flask in one beaker and the smaller beaker into the other. Make sure they do not sink. Leave them to adjust to the temperature and constantly check the temperature to make sure it is right.

* Using the graduated pipette, 10cm3 of Hydrogen Peroxide should be obtained and placed into the syringe.

* Check that the gas syringe is set at 0

* Apply pressure to the syringe containing the Hydrogen Peroxide until all the contents have been added to the conical flask.

* Immediately start the stopwatch. Take readings of oxygen evolution every 20 seconds and record them in a table. After 300 seconds stop recording results.

* Wash thoroughly the entire system and repeat the above steps using the different temperatures of 20, 30 40 50 and 60oC. For the higher temperature a heating system should be used instead of a cooling system.

* Ideally three sets of results should be obtained for each temperature

Evaluation

I conclude that generally

(I have no time left to finish but will complete at earliest available opportunity)