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The effect of concentration in the rate of enzyme catalysed reaction

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The effect of concentration in the rate of enzyme catalysed reaction Aim: To investigate how altering the concentration of the substrate, hydrogen peroxide, affects the rate of a catalytic reaction. Hydrogen peroxide (H202) is a toxin, which is a by-product of metabolism, namely anaerobic respiration. Hydrogen peroxide (H202) is a colorless and transparent liquid, which is relatively stable and so requires the presence of catalase in order to decompose during anaerobic respiration. It is a poisonous toxin and must be broken down into harmless by-products in order to be removed from the organism's body. Catalase is one of the fastest acting enzymes in an organism's body. It catalyses hydrogen peroxide, producing water and oxygen. A single molecule of the globular protein decomposes 40,000 molecules of H202 per second. The catalase is responsible for producing 1012 molecules of oxygen per second. For this experiment, I am going to use yeast as the catalase. The reaction between hydrogen peroxide and catalase is illustrated in the equation below; Predictions: I predict that as the concentration of the hydrogen peroxide increases, there will be a greater number of collisions between the substrate, hydrogen peroxide, and the enzyme catalase. Because of the collision theory, where there is an increased probability of molecules colliding as the concentration of molecules increases, I predict in increased rate with increased substrate concentration. However, I am going to keep the enzyme concentration the same for all conditions so I anticipate that there will be a saturation point, where all of the enzyme active sites will be in use by substrates or products, and so there will be a point where the rate of reaction will plateau out. For lower concentrations of the hydrogen peroxide, I predict that the rate of reaction will be directly proportional to the concentration of hydrogen peroxide in each solution. If I double the concentration of the hydrogen peroxide, there will be twice as much volume of solution. ...read more.


At lower temperatures, the particles have less kinetic energy and will move slower, resulting in less collisions at the right energy level, and so a reduced rate of reaction. Also, enzymes work best at an optimal temperature of 35�C, because this best matches the temperature of the human body. At higher temperatures, enzymes become denatured. This is where their chemical bonds break and the activation sites change shape. This means that the lock and key function is not in place so the chemical reaction is much slower. Diagram 1, below shows particles at lower temperatures, where reactions are reduced. Diagram 2 shows particles at higher temperatures where there is an increase in the number of collisions Concentration Increasing the concentration means increasing the number of molecules in a particular volume. This means that there will be more particles or molecules that can collide. A reduced concentration means that water has been used to dilute the solution, which means that the reactant particles are further apart, so less collisions. If there is a high concentration of hydrogen peroxide, this will mean that it will react more with the yeast, and there will be a greater volume of the byproducts in a given time. Pressure Increasing the pressure of a gas plays the same role as increasing the concentration of a solution. Increasing the pressure means that particles are compressed into a smaller area, so they will collide more. If the same number of particles is exposed to lower pressures, they will collide less as the area they are in will increase. Surface Area Smaller particles will have a greater reaction rate than larger particles. This is because smaller particles have a larger surface area: volume ratio. Therefore, those with a larger surface area will have a larger area on which the reaction can take place. Thus, they will have in increased rate of reaction compared with particles of large surface area. ...read more.


A fluctuation of any of the measuring would have adversely affected the results, resulting in biased, anomalous, or incorrect readings. The major factors that could have influenced my results were: * Fluctuations in the setting up of the experiment. If some air had become trapped in the apparatus, this would have resulted in a reading far greater than the actual results * Accuracy of diluting of hydrogen peroxide. If this was not done accurately, this would have affected the reaction rate * Gradual breakdown of the hydrogen peroxide due to exposure to sunlight means that the results were not 100% accurate. Unfortunately, it was not possible to do this experiment in the dark. Nor was it possible to conduct this experiment at low temperatures as the enzyme needed to be as close to its optimum temperature as possible. Unfortunately, increased temperatures also facilitated the breakdown of hydrogen peroxide * Accuracy of measuring the volume of gas. The volume of solution would have had to be measured at the meniscus to ascertain what volume of gas was in the cylinder Evaluation Although my results did support my predictions, I do not believe that there were a significant number of results to determine an accurate initial rate of reaction for each concentration of hydrogen peroxide. Furthermore, perhaps I should have measured the volume of gas in the tube for more than 45 seconds. There didn't appear to be any real anomalies in my results, but again, it would have been wise to conduct more experiments on the varying concentrations of hydrogen peroxide. Unfortunately, due to time constraints, there was little time to undertake an initial study to determine how to collect my results. I think that if I could have conducted this again, I would have counted the number of bubbles emitted as a result of hydrogen peroxide breaking down to water and oxygen. The theories behind this experiment appear to be sound and the collision theory supports my predictions. ?? ?? ?? ?? Amanda Gaber March 2006 Page 1 of 11 ...read more.

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