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An Investigation on the Effect of Enzyme Concentration on rate of hydrogen peroxide breakdown.

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Introduction

An Investigation on the Effect of Enzyme Concentration on rate of hydrogen peroxide breakdown Planning Aim The aim of this investigation is to study how the rate of reaction i.e. rate of substrate breakdown. is affected by varying the concentration of the enzyme. The enzyme that is used in this investigation is catalase, which is sometimes referred to as peroxidase. The substrate is hydrogen peroxide. Celery extract is used in this investigation to provide the catalase, and a solution of hydrogen peroxide will have been prepared beforehand. Background Knowledge * Introduction Our liver has the vital function of detoxifying any poisons that may be absorbed with food or produced as a wasted product by the body itself. Hydrogen peroxide (H2O2) is one such example. This highly toxic chemical is a waste product of the deamination of amino acids in the liver. If the amount of hydrogen peroxide builds up to large amounts, the poisonous material can quickly kill cells. Therefore, the body needs a mechanism of breaking down harmful materials such as hydrogen peroxide. Hydrogen peroxide will breakdown to harmless products without the use of enzymes. However, the reaction is so slow that levels would rapidly increase which would result in death of that organism. One method of rapid detoxification is the use of enzymes, these act as catalysts which greatly increase the rate of chemical reactions, therefore, maintaining a safe level of H2O2 in the body. The enzyme, catalase, is responsible for detoxifying hydrogen peroxide. Catalase has one of the highest turnover numbers for all known enzymes (40,000,000 molecules/second). This high rate shows the importance for the enzymes capability for detoxifying hydrogen peroxide and preventing the formation of carbon dioxide bubbles in the blood. The liver contains many different types of enzymes, including catalase, each capable of breaking down one type of poison. This is the reaction that takes place between the substrate and the enzyme: CATALASE 2H2O2 2H2O + O2 The effect of catalase on hydrogen peroxide has already been observed in a previous experiment where a small piece of kidney, used to provide the catalase, was reacted with hydrogen peroxide. ...read more.

Middle

3. The rubber bung and delivery tube was fitted securely into the neck of the conical flask and the flask was supported so that the end of the delivery tube was below the burette. 4. Using the 10cm� syringe 10cm� of hydrogen peroxide was carefully introduced through the open tube in the bung. A good seal with the syringe was ensured. As the hydrogen peroxide was added the flask was being gently stirred. 5. The stopwatch was started immediately and the level of water in the burette was recorded at 0, 1, 2 and 3 minutes. 6. Three dilutions of celery extract were made using the equipment and steps 1-5 were repeated for each dilution. The conical flask was rinsed out thoroughly with distilled water between dilutions. 7. the concentrations that were used were: 100%, 75%, 50%, 25% and a control of distilled water 0%. The table below shows volumes of celery extract and water to use for each concentration to ensure that the same volume of celery extract was used. Celery Extract (%) Vol. Of 100% celery (cm�) Vol. Of distilled water (cm�) 100 2 0 75 1.5 0.5 50 1 1 25 0.5 1.5 0 0 2 Results The results from the experiments have been tabulated in different forms to make them easier to understand and study. The table below shows the level of water left in the burette at the specified times, for the reaction between celery extract and H2O2. Table No.1 Conc. Of celery Extract (%) Level of water in burette (cm�) at time (min) for each set of experiments 0min 1min 2min 3min 100 45.8 20.3 18.0 14.5 75 43.1 25.9 24.4 22.9 50 42.3 29.0 27.8 26.3 25 42.5 31.3 30.5 29.7 0 43.2 43.2 43.2 43.2 Below is a table which shows the effect of enzyme concentration on the volume of O2 produced from the reaction with H2O2. ...read more.

Conclusion

Problems that arose from this were that air was forced out of the delivery tube when the syringe was pressed (giving a false reading instantly). Also, not all of the 10cm3 of hydrogen peroxide was introduced to the catalase because some of this got trapped at the end of the syringe. To stop this from happening a larger syringe could be used eg. a 20cm3 syringe. This way all the hydrogen peroxide would be forced out because there would be an extra 10cm3 of air to push it. However with this it would mean that there would be even more air pushed into the burette to start with. To make it so that the burette did not have that extra air in, the 0 minute reading could be taken after all the contents of the syringe had been pushed into the conical flask. At this point the stopwatch would start and the rest would carry on as usual. The clamp holding the burette up also caused a problem because sometimes it obstructed the view of the markings. Therefore making it hard to read the volume off. To fix this the burette could be held up with something else. For example it could be held up by a piece of string, which was then clamped. Improvements Below are a set of possible improvements to the investigation that could have offered a more varied and accurate set of results: A datalogger with a oxygen sensor could have been used instead of the burette configuration. The datalogger would then process detailed graphs of the course of the reaction to see how reaction rates differ with time using much smaller time intervals than 1 minute. More accurate graphs of rate of reaction according to enzyme concentration would also be produced. A more plentiful source of catalase could be used e.g. liver, this means more oxygen would be produced in total, therefore reducing the percentage error in measurements, and also the reaction would last for much longer thus presenting more accurate results and graphs. Sean Fang 12SD ...read more.

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