Enzyme Lab Write Up- Rebecca Sennaraj

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Dec 6, 2023

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Rebecca Sennaraj Ms. Bradford AP Biology 10/17/2023 Introduction : In this procedure, the function of enzymes was investigated. The experiment was designed to determine the rate of reaction for enzyme catalyzed reaction, and to see how the conditions, such as enzyme concentration, temperature, pH, substrate concentration, affect the initial rates of reaction. To do so, first, the initial baseline rate of reaction, with no change in condition, was determined. This was achieved by measuring the rate of appearance of the product which in this case was O 2 . To find the baseline rate of reaction, 3% hydrogen peroxide solution was mixed with the enzyme solution which is a catalase yeast solution. Upon mixing these two solutions, the amount of product/gas that is produced in the reaction chamber was measured. The initial rate was then determined when the rate of reaction seemed to be constant, which would be between the first and second minute. Then the amount of product formed at one minute was subtracted from the amount of product formed at the second minute, and then it was divided by 60 seconds, to give the initial rate of reaction. The same procedure was repeated for the different conditions, and the reaction rate was calculated, using the same equation before: (final amount of product- initial amount of product)/ time. Data : Part B: Avg. rate @ 25% Catalase Concentration: 0.0225 mL/s ± 0.02 Avg. rate @ 50% Catalase Med Concentration: 0.0531 mL/s ± 0.025 Avg. rate @ 75% Catalase High Concentration: 0.044 mL/s ± 0.026 Part C: Avg. rate @ 5 degrees Celsius: 0.0376 mL/s ± 0.004 Avg. rate @ 37 degrees Celsius: 0.2135 mL/s ± 0.017 Avg. rate @ 100 degrees Celsius: 0 mL/s ± 0 Part D: Avg. rate @ pH of 4: 0.0594 mL/s ± 0.019 Avg. rate @ pH of 7: 0.1186 mL/s ± 0.02 Avg. rate @ pH of 10: 0.1421 mL/s ± 0.009

Part E: Avg. rate @ 0.3% H 2 0 2 solution: 0.0545 mL/s ± 0.009 Avg. rate @ 1.5% H 2 0 2 solution: 0.09875 mL/s ± 0.012 Avg. rate @ 3.0% H 2 0 2 solution: 0.171 mL/s ± 0.017 Graph: Why is baseline reaction important?* : In our group, the determined average value of the baseline reaction rate is 0.143 mL/s. O. This is calculated by finding the constant part of the rate of reaction graph, and then finding the difference in appearance of the product, and then dividing this value by the time: Δ O 2 gas / Δtime. In this context, the baseline reaction rate serves as the control variable for this experiment. In order to determine how these different conditions affect the rate of reaction, there must be a value that it can be compared to: the baseline rate of reaction. As a result, it is possible to determine whether the rate of reaction increases or decreases or stays the same in accordance to conditions the experiment is placed in.

*I do not have the baseline reaction data since I wasn’t there. How does each condition affect the function of the enzyme catalase? Enzyme concentration impact: The reaction rate for an enzyme catalyzed reaction is directly dependent on the concentration of the enzyme. This is because if the enzyme concentration increases, then more enzymes will be available to help catalyze the reaction resulting in a greater rate of reaction. Because enzymes reduce the activation energy for a reaction to take place, an increased concentration of enzymes reduces the activation energy required to a greater extent. The rate of an enzyme-catalyzed reaction is directly dependent on the enzyme concentration. However, it can only increase to an extent since the enzymes must react with the substrate to convert it into product. As the reaction proceeds the substrate becomes saturated, there will be nothing for the enzymes to bind to. Therefore, if you have an excess of enzyme but not enough substrate, the reaction rate will be less. This explains the lower reaction rate for a 75% Catalase solution, in comparison to 50% and 25% catalase solution. Temperature impact: As the temperature increases, the reaction rate increases. This is because there is more kinetic energy due to the increased temperature which results in more collisions which increases the likelihood that substrate will collide with the active site of the enzyme, thus increasing the rate of an enzyme-catalyzed reaction. However, this is only at generally low temperatures. At higher temperatures, the enzyme gets denatured, and the rate of the reaction dramatically decreases which is exemplified with the 0mL/s reaction rate at @ 100 degrees Celsius. pH Impact : As the pH increases, the reaction rate increases because the optimal pH value for the catalase used in this experiment is closer to a pH of 10. This is because enzymes- proteins- are sensitive to the changes in hydrogen ion concentration. In extreme levels of hydrogen ions, enzymes are denatured at some pHs because a change in hydrogen ion concentrations alters the enzyme's acidic and basic side groups, along with the substrate’s components. For an enzyme to bind its substrate, it must have a charge in the active site. A change in pH can alter an enzyme’s catalytic activity since it can neutralize the charges located in the active site. An enzyme is able to reduce the reaction’s activation energy the most in a narrow range of pH. In this context, the optimal range is at a pH of 10 since it has the highest reaction rate. In addition, it is clear that the enzyme is denatured at lower levels of pH, since the reaction rates are much lower. Substrate Concentration Impact: The reaction rate is directly proportional to the concentrations of the substrate. At a lower substrate concentration, most active sites of enzymes are not filled, but when there is a higher substrate concentration, there are more collisions due to

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the number of collisions, so the likelihood that substrate will collide with the active site of the enzyme increases, and the activation energy for the reaction decreases, and the reaction occurs faster. However, this is only until the limit of enzymes is reached. This is because there needs to be enough enzymes for the substrate to react with, and if there is more substrate than enzyme, the reaction cannot occur anymore. However, this is not applicable in the context of this experiment, since the reaction rates are consistently increasing as the substrate concentration increases. Presence of Error in Experiment : There are plenty of places for human error in this experiment ranging from inaccurate readings of the amount of product produced to incorrect proportions when forming the solutions necessary to change the pH, enzyme concentration, and substrate concentration. Therefore, it is important to use error bars when displaying the initial rates of the experiments. The standard error bars demonstrate the uncertainty in the rates and give a general idea of how precise the measurement is and the rough range the true rate of reaction is in.

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