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Investigating an enzyme-controlled reaction: catalase and hydrogen peroxide concentration

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Investigating an enzyme-controlled reaction: catalase and hydrogen peroxide concentration Date: 08/05/09 Aim: To investigate the rate of oxygen production by the catalase in pureed potato as the concentration of hydrogen peroxide varies Hypothesis: I predict that as the concentration of hydrogen peroxide increases, the rate of reaction will increase until the pureed potato becomes saturated with the hydrogen peroxide. If the reaction reaches saturation point, no more reaction will be occurred. The reason that the rate of reaction increases is that more substrates can react with more active sites of the enzyme when the concentration of hydrogen peroxide increases. As a result, the more oxygen will be produced in the high concentration of hydrogen peroxide. 10% of hydrogen peroxide will produce 10cm3 of oxygen from every cm3 that decomposes. In this procedure, 2 cm3 of 10% hydrogen peroxide will release 20cm3 of oxygen if the reaction goes to completion. Variables * Independent:-The different concentration of hydrogen peroxide * Dependent:-The rate of reaction (the amount of oxygen produced) * Controls: - Standard Pressure and temperature of the room - Measuring equipments are kept consistent - The amount of pureed potato - The constant temperature of hydrogen peroxide and potato Data Collection Table 1: The amount of oxygen produced in the different concentration of hydrogen peroxide Concentration of hydrogen peroxide% (mol L-1) The amount of oxygen produced in 30 seconds (�0.01s) Trial 1 (�0.05mL) Trial 2 (�0.05mL) Trial 3 (�0.05mL) Trial 4 (�0.05mL) Trial 5 (�0.05mL) Distilled water 0.00 0.00 0.00 0.00 0.00 5% 2.00 2.00 2.00 1.00 2.00 10% 3.00 2.00 4.00 3.00 3.00 15% 6.00 5.00 5.00 4.00 5.00 20% 5.00 6.00 5.00 6.00 6.00 25% 5.00 6.00 5.00 7.00 8.00 ?Observation: As soon as the 2cm3 of hydrogen peroxide was added in the conical flask which contained the pureed potato, air bubbles begun to be produced and gathered in the measuring cylinder through the tube. ...read more.


The substrate molecules need time to join onto the enzyme and to leave it so the maximum rate achieved is always slightly below the theoretical maximum. The time taken to fit into and leave the active site is the limiting factor in the rate of reaction. The diagram below shows what happens V. EVALUATION POST-LAB SURVEY OF STUDENTS' CONCEPTIONS Have students retake the Pre-Lab Exercise. Compare pre-lab and post-lab responses. TRADITIONAL 1. Describe the general structure and function of an enzyme? Answer: An enzyme is a 3-dimensional molecule composed of long chains of amino acids, held together by peptide bonds. They are catalysts that make biochemical reactions possible. 2. Describe what happens in an enzyme catalyzed reaction. Include diagrams in your explanation. Answer: During an enzyme catalyzed reaction the enzyme bonds with a specific substrate at the active site. This is called an enzyme-substrate complex. The substrate is converted into a specific product, but the enzyme remains unchanged. Enzymes accelerate reactions by factors of at least a million. 3. Describe what will happen to the rate of an enzyme controlled reaction if the initial concentration of substrate is increased. Answer: As the initial substrate is increased, the initial reaction rate will increase up to the point where all the enzyme molecules are engaging at their maximum rate. Beyond this point the rate of reaction will remain constant (level off). Initial Reaction Rate Concentration of Substrate 4. Describe what will happen to the rate of an enzyme-controlled reaction if higher concentrations of the enzyme are used. Answer: As more enzyme is added initially to the substrate, the reaction rate will increase up to the point where all there are too few substrate molecules to allow all of the enzyme molecules to collide with them and catalyze the reaction at the maximum rate. At that point no additional increase in the initial rate of reaction will occur. ...read more.


For example, the rate of reaction at an enzyme concentration of 15 potato discs was 35 + or - 4. This results in an error of uncertainty of 11% The shape of the graph is as I predicted showing that as enzyme concentration increases so does the rate of reaction. This is because at a greater enzyme concentration, there are more free active sites available for the substrate and so more products can be made in a shorter length of time. However, it is not possible to take precise readings from the graph between the plotted points since insufficient readings were taken. To be able to do this, intermediate enzyme concentrations would have to be measured so that the shape of the graph would be more exact. Suggestions and Improvements - To create a more accurate experiment in the future, several precautions or alterations can be made: � Instead of using potato discs that have slight variations in size, and volume of catalase, as a source for the enzyme, a 1 molar solution of the enzyme could have been diluted to create different concentrations. This way the concentrations can be measured far more accurately reducing the chances of errors in the investigation. � In this experiment 8 enzyme concentrations were considered. However, although there was a large range, insufficient intermediate measurements were made creating gaps between the measurements where guess work is needed to predict the rate of reaction at these points e.g. point A on graph "Chart 2". In a future investigation, a far greater number of enzyme concentrations between those already recorded should be tested reducing the extent of any anomalies on a graph where the line of best fit must be drawn. � In this investigation each reading was repeated so that an average rate of reaction for each enzyme concentration could be calculated. This could be improved by repeating the reading more frequently thus reducing the extent of any anomalies further, once averaged. ?? ?? ?? ?? ...read more.

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