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Investigating the effect of substrate concentration on reaction between Hydrogen Peroxide (H2O2) and the enzyme Catalase.

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Investigating the effect of substrate concentration on reaction between Hydrogen Peroxide (H2O2) and the enzyme Catalase AIM Catalase is an enzyme found in Yeast, and when yeast reacts with H2O2, a reaction occurs, with H2O2 acting as the substrate, and Catalase being the complementary enzyme. In this experiment, I will analyse, interpret, conclude and evaluate the effects of reacting different concentrations of H2O2 with the enzyme Catalase and hence, use it to understand the effects on the rate of the reaction. My main aim is to understand how enzymes work under varied conditions. Yeast is not a chemical and has no chemical formula. Try looking at yeast as a single cell, similar to any single cell in your body. Those cells are made up of numerous types and classifications of chemicals. Some are very simple, like water. Others are extremely complex, like proteins. As the enzyme Catalase is not available in pure form, I will use yeast as the source of enzyme. There are other alternatives e.g. potato tubes which also contain catalase, but using yeast would give me greater accuracy because the amount of Catalase in each potato tube would be different. BACKGROUND INFORMATION Enzymes are biological catalysts, which means that they speed up biological reactions without getting used up themselves. They also provide a control mechanism for reactions, as the amount of enzyme available determines how quickly a reaction can happen. Enzymes are globular proteins that have a specific shape. They contain a 'depression' called the 'active site' and this is the main area for reactions to occur. The 'substrate' is what the enzyme acts on and breaks down. Enzymes are 'specific' because their active sites have specific shapes and only substrates that have a complementary shape can fit into the enzymes active site, thus causing a reaction. There are 2 theories, which describe the way enzymes function: 1) The Lock and Key Theory + Enzyme + Substrate Enzyme Substrate Complex Enzyme molecules are constantly moving about within a cell and when an enzyme molecule collides with a substrate molecule, the substrate binds to the enzyme's active site. ...read more.


3) Measure out the different concentrations of hydrogen peroxide solution using the following table as a guide. To measure out the concentrations, pour the required amount of solution from its designated beaker into the measuring cylinder until the required amount is reached. Place the solutions in separate test tubes and label them using an appropriate method. In my case I used sticky labels. Concentration (%) Amount of H2O2 needed (cm2) Amount of H2O needed (cm2) 100 20 0 90 18 2 80 16 4 70 14 6 60 12 8 50 10 10 40 8 12 30 6 14 20 4 16 10 2 18 0 0 20 4) Record the room temperature and measure out 1g of yeast with the weighing scale. Be sure to measure it out accurately to prevent defects in the results. 5) Take the test tube with 100% concentration and pour the contents into the conical flask. 6) Add the yeast to the conical flask and immediately seal the conical flask with the cork and start the stopwatch. To make sure that all the yeast is reacting with the substrate solution, swirl the conical flask slowly so that all the yeast gets in contact with the solution. Note that too much swirling will increase the kinetic energy of the molecules so the rate of reaction will increase, therefore take caution in ensuring that the conical flask is not swirled excessively. 7) Pay attention to the gas syringe and stop the stopwatch as soon as 100ml of gas is produced and record the time taken in a table. If 100ml of gas is not produced then record the final amount of gas produced. The reason that I'm measuring up to 100ml of gas is because the gas syringes that are available to me have a maximum of 100ml on the scales. 8) Wash and dry out the conical flask and reset the stopwatch. ...read more.


5. The yeast that I used in each of the experiments was different. The reason for this is because I carried out each of my experiments at different times and the tubs of yeast made available to me could have changed each time. For my final repeat, I used a new tub of yeast and this gave me much faster rates of reaction than the first 2 attempts. My assumption is that the first batch of yeast must have been tampered in some manner by any of the previous users, because it had a powdery appearance whereas the new tub that I used was in granules. This imperfection did affect my results but most importantly did not affect the general trend of the results. If I were to repeat my experiment, I would use the same sample of yeast for all my experiments. 6. It is very difficult to control the amount of swirling of the conical flask while the reaction is taking place. Swirling excessively will result in an increase of kinetic energy of the enzyme and substrate molecules therefore they will move around faster and collide more, so this will cause the rate of reaction to increase. No swirling could lead to some of the yeast not getting into contact with the substrate solution and this would cause the reaction to be incomplete. The method I used to overcome any abnormalities and to get a fair test was to swirl the conical flask 3 times for 360o each time and maintaining a constant speed of swirling. Obviously the amount of swirling cannot be exactly the same each time but I did my best to swirl the conical flask by the same amount each time. ALTERATIONS I only made a slight alteration to my method. In my method I mentioned that I will control the pH by storing it in a buffer solution, but I realised that there was no need for this as the pH would remain constant anyway. Biology Coursework Ismail Lakhi ...read more.

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