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Investigation of the effect of substrate concentrationon the rate of activity of the enzyme catalase

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Investigation of the effect of substrate concentration on the rate of activity of the enzyme catalase Background Information: Enzymes are biological catalysts that increase the speed of chemical reactions without undergoing any physical change. They are neither used up in the reaction nor do they appear as reaction products. All enzyme catalysed reactions are reversible. Enzymes effectively lower the amount of activation energy required for chemical reactions to start. Some enzymes weaken covalent bonds within the substrate molecule, whereas in other cases this lowering of the activation energy seems to take place because the enzyme holds the substrate molecules in a particular position that increases the likelihood that the molecules are going to react. The graph below shows how the activation energy is lowered when enzymes are present; The enzyme and substrate form an enzyme-substrate complex (Savante Arrhenius 1888 Swedish scientist). One theory of this is the lock and key hypothesis. According to this hypothesis the enzyme molecule can only bind with a substrate with a complementary shape to fit its active site, like a lock and a key. However, another theory of how the enzyme-substrate complex binds together is the induced fit hypothesis (Koshland). This hypothesis suggests that some enzymes undergo small modifications to the active site when they form a complex with the substrate. Within cells, hundreds of reactions occur all the time, however they don't happen at room temperature, as it is too cool, if they do, then it is a very slow reaction. Which is why enzymes are so important. The human body is still quite cool for reactions to occur, but enzymes work very well at body temperature, so speeding up the reactions. However enzymes can be denatured if the temperature or the pH is too high, or if the concentration of ions is too high. If the enzymes become denatured the structure becomes disrupted and cannot return to its original shape. ...read more.


Remember to wash the apparatus out in between each experiment. Repeat this experiment three times per different concentration of hydrogen peroxide, by taking several readings for each enzyme concentration, the results could be averaged, to minimize chances of inaccuracies. The apparatus used are as follows: * Two clamps, to hold the boiling tube and gas syringe steady. * 100cm gas syringe, as no more than 100cm of O2 would be collected, and if it were a 50cm then it wouldn't be big enough to collect all the oxygen. * 5 boiling tubes. One for each concentration of hydrogen peroxide. This ensures even more that the different concentrations will not mix. Although they must be washed out between each repeat experiment. * 5 5cm syringes for each of the different concentrations. This ensures even more that they don't mix. * 1 2cm syringe for the yeast. There is no need to have more than one, as there is only one concentration of yeast. (See plan for why there are different sized syringes for the yeast and for the hydrogen peroxide.) * 5% vol of yeast. At least 30 ml of it so that there is enough for each test. (2cm for each test.) * At least 12ml of each concentration of hydrogen peroxide, so there is enough for each repeat test (4cm for each test). Concentrations- 100%, 80%, 60%, 40% and 20%. * An open bore needle so that you can inject the hydrogen peroxide into the boiling tube, through the bung, ensuring less oxygen escapes. * A stop clock. * A test tube rack-to keep the boiling tubes at room temp, instead of holding them-stops heat from hands warming boiling tubes. Hydrogen peroxide is an irritant (see background information) so to work safely, and to protect myself from any damage; I shall wear safety goggles, a lab coat, and rubber gloves. At the end of the experiment, the bench should be disinfected in case there are any spillages such as hydrogen peroxide left on the bench. ...read more.


The major limitation in this experiment was the time. Meaning that only 5 concentrations could be used, and there was not enough time to repeat each test more than 3 times, therefore only general, overall trends could be identified in the results. They can only be approximated and are not necessarily accurate. A further cause of inaccuracy is individual operator error, for example whilst reading the meniscus, to measure the volumes, slightly different eye-level positions would cause slight over or under estimations. To make this experiment more accurate in the future, a greater number of substrate concentrations between those already recorded should be tested reducing the possibility of any anomalous results. To reduce the chance even more, repeat each test far more than 3 times. In the experiment I could have recorded how much gas was collected every 10 seconds, up to 1 minute, for an even more accurate set of results. If I had had the equipment and the time, I would have used an incubator to keep the temperature constant. I tried to keep the syringes as accurate as possible, i.e. as 2cm of yeast was used I used a 2cm syringe and checked to see if the meniscus was lined up to the correct mark. For the hydrogen peroxide, 4cm was being used, there was no 4cm syringes available so I used the closest size to it which was a 5cm syringe, and checked the meniscus again. However, again if I had the correct resources, I would have used a micropipette as this can measure extremely small measurements, such as a tenth of a millimetre. My results were moderately reliable as all the repeat tests were within 1cm of each of the same concentration tests. E.g., for the 20% concentration, the 3 results were; 20, 19 and 20. Causing the average to be 19.67 to 2dp. However my result's unreliability was mainly due to the fact only one variable could be controlled, all other factors that increased the rate of reaction could not be kept constant. In spite of this, the experiment has proved my hypothesis. - 1 - ...read more.

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