Enzyme Catalysis And Substrate Binding Biology Essay

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Enzymes are proteins that speed up reactions in cells. Each of these enzymes speed up the reaction by binding to a substrate at the enzyme's active site causing this substrate to split into the reaction's products. These enzymes work by reducing the activation energy of a reaction so that the reaction is easier to start.1 Each individual enzyme catalyzes thousands of reactions per minute and is crucial to the processes of a cell. One of these enzymes is catalase which breaks down hydrogen peroxide (H2O2) into water and oxygen. It does this by undergoing a decomposition reaction to form these products.2 In this experiment, a solution of hydrogen peroxide will undergo a reaction with catalase to see the rate that hydrogen peroxide is consumed over a set interval. The reaction must be stopped at a certain interval, so sulfuric acid must be added to change the pH so that the catalase denatures. To measure how much hydrogen peroxide is used, a compound called potassium permanganate (KMnO4) is added to react with the excess hydrogen peroxide. This process works because the hydrogen peroxide and potassium permanganate are reactants in the reaction, so when all of the hydrogen peroxide is used up, the potassium permanganate turns the solution to a brown color.3 The purpose of this experiment is to find the reaction rates of catalase and hydrogen peroxide over a certain time period as compared to the normal decomposition of hydrogen peroxide. It is hypothesized that the catalase catalyzed reaction will follow a logarithmic curve as less hydrogen peroxide is readily available over time. It is also hypothesized that more hydrogen peroxide will be decomposed in 60 seconds in the presence of catalase than in the 3 days of natural uncatalyzed decomposition of hydrogen peroxide.

Materials and Methods

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Catalase Extract

1M H2SO4

2% KMNO4 solution

Distilled water

1.5 % H2O2

9: 60 mL beakers

2: 5 mL syringes

2: 10 mL syringes

Stopwatch

Experiment 1:

10 mL of 1.5% H2O2 is placed into a beaker. Add 1 mL of water to the beaker then 10 mL of 1M H2SO4 to the beaker and mix well. Remove a 5 mL sample from the beaker to use for the titration. To titrate, take 5 ml of the 2% KMNO4 solution and add one drop at a time, swirling each time before adding another drop. Continue this until there is a lasting color change in the beaker. Record the amount of 2% KMNO4 solution used.

Experiment 2:

Add 15 mL of H2O2 to a beaker and leave it uncovered for 24 hours. After the 24 hours is up, repeat the titration process from experiment 1 and record the results.

Experiment 3:

Add 10 mL of H2O2 to 7 beakers. Add 1 mL of catalase to each beaker and measure out times of 10 seconds, 30 seconds, 60 seconds, 120 seconds, 180 seconds, and 360 seconds. At each interval, add 10 mL of 1M H2SO4 to the beaker and mix well. After each reaction has been stopped, repeat the titration process from experiment 1 on each beaker and record the results.3

Results

Table 1- Initial and Final Readings of H2O2: Base line

Base Line Readings

Initial Reading

5 mL

Final Reading

8.5 mL

Table 2- Initial and Final Readings of H2O2 Naturally Decomposed

Natural Decomposition Readings

Initial Reading

5 mL

Final Reading

8.5 mL

Table 3- Initial and Final Readings of H2O2 Decomposed in a Catalyzed Reaction

10 sec Readings

30 sec Readings

60 sec Readings

90 sec Readings

120 sec Readings

180 sec Readings

360 sec Readings

Initial Reading

5.0 mL

5.0 mL

5.0 mL

5.0 mL

5.0 mL

5.0 mL

5.0 mL

Final Reading

8.2 mL

8.0 mL

7.4 mL

7.4 mL

7.0 mL

6.8 mL

6.6 mL

Discussion

In this experiment, it was hypothesized that the decomposition of hydrogen peroxide in a catalase- catalyzed reaction will follow a logarithmic curve, and that more hydrogen peroxide will be consumed in the catalyzed reaction in 60 seconds than the natural decomposition over 3 days.

Table 4: Amount of H2O2 Consumed

10 sec Readings

30 sec Readings

60 sec Readings

90 sec Readings

120 sec Readings

180 sec Readings

360 sec Readings

Base Line Amount

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3.5 mL

3.5 mL

3.5 mL

3.5 mL

3.5 mL

3.5 mL

3.5 mL

Initial Reading

5.0 mL

5.0 mL

5.0 mL

5.0 mL

5.0 mL

5.0 mL

5.0 mL

Final Reading

8.2 mL

8.0 mL

7.4 mL

7.4 mL

7.0 mL

6.8 mL

6.6 mL

Amount of KMnO4 Consumed

3.2 mL

3.0 mL

2.4 mL

2.4 mL

2.0 mL

1.8 mL

1.6 mL

Amount of H202 Used

0.3 mL

0.5 mL

1.1 mL

1.1 mL

1.5 mL

1.7 mL

1.9 mL

After examining Table 4 and Table 2, the hypothesis is proven correct by two factors. The first factor is that the rate of the catalase catalyzed reaction is tapering off over time. An example of this is that it takes 60 seconds to decompose 0.2 mL of hydrogen peroxide (120 sec to 180 sec), but the it takes 180 seconds to decompose the same amount. All of this slowing down is illustrated in Figure 1. This slowdown is due to the fact that the more hydrogen peroxide is decomposed, then the less hydrogen peroxide is readily available. At a molecular level, this comes down to the enzymes having trouble finding hydrogen peroxide in the solution thus less of it is decomposed. The second factor that proves the hypothesis true is the fact that there was no change in the amount of hydrogen peroxide in the beaker after being left out for 3 days. This is due to the fact that the decomposition of hydrogen peroxide is an extremely slow process that can take months before and noticeable change is found in the amount of hydrogen peroxide available. This slow decomposition is the reason that enzymes are an essential part of all cellular processes because large amounts of hydrogen peroxide can be lethal to a cell. With these factors in mind, the hypothesis is proven correct in all aspects and this experiment shows the necessity of essential enzymes that help all cells maintain a balanced equilibrium.

Figure 1: Amount of Hydrogen Peroxide Used Over Time

Citations

Campbell, Neil A., and Jane B. Reece. Biology. 7th ed. San Francisco: Pearson, 2005. 151. Print.

George, P. "Reaction Between Catalase and Hydrogen Peroxide." Nature 12 July 1947: n. pag. Web. 11 Nov 2010. <http://www.nature.com/nature/journal/v160/n4054/abs/160041a0.html>.

Biology Lab Manual for Students. The College Board, 2001. 19-22. Print.