study of the enzyme catalysis

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Introduction

In biological settings, enzymes are important in order to stimulate reactions that normally wouldn't happen as quickly by catalyzing reactions so that they require less activation energy than without the enzyme present. In an enzyme-catalyzed reaction, the substrate binds to the active site of the enzyme, causing a temporary drop in the energy required to activate the reaction of the molecule so that the product of the reaction is formed.2 After the enzyme has completed it's task, it is then recycled to be used again in another reaction. However, enzymes are specific to particular reactions, because of its structure.2 In organisms, catalase stimulates the reaction where hydrogen peroxide is decomposed into water and oxygen.1 This process is measured by the equation 2 H2O2 2 H2O+O2 (gas).3 This enzyme is found specifically in mammalian tissues to prevent a build-up of the peroxide in tissues, therefore causing damage.1 In this experiment, hydrogen peroxide was placed into beakers with sulfuric acid and then titrated to create a base line for the experiment. After this was established, the catalase will be placed into the mixture at for different times, and then titrated. Therefore, the mixture with the catalase in it for the most amount of time should show a change in color faster when titrated than that of the base line or mixtures that held the catalase in them for shorter amounts of time.

Materials and Methods

100 mL of 1.5% H2O2

Distilled Water

55 mL of KMnO4

70 mL H2SO4

7 mL of Catalase

Pipettes labeled H2O2 , KMnO4 , H2SO4 and Titrate

12 beakers

Stop Watch

Labels for the cups

Establishing a Base Line

Place 10 mL of the 1.5% H2O2 solution into a clean cup

Add 1mL of H2O to the cup, this will later be replaced by the catalase

With extreme care, add 10mL of H2SO4 to the cup

Mix the solution well

Remove a 5mL sample of the solution and place into another cup to be titrated

Using a 5mL pipette, add the KMnO4 one drop at a time, until a pink or brown color is achieved and sustained.

Record readings

Uncatalyzed Rate of H2O2 Decomposition2

Place 15mL of 1.5% H2O2 into a beaker

Store the solution, uncovered, for 24 hours at room temperature

Repeat steps 2-5 from the "Establishing a Base Line" to conclude the amount of H2O2 remaining in the beaker.

Record findings

Enzyme-Catalyzed H2O2 Decomposition

Label 7 beakers with 10, 30, 60, 90, 180, and 360. This will be the amount of seconds the catalase will be in the H2O2 solution.

Add 10mL of the solution into each of the beakers

Add 1mL of the catalase and use the stop watch to time the reaction

Gently swirl for the amount of time listed (ex. If 10s, swirl for 10s etc.)

At the correct time, add 10 mL of H2SO4

Once this has been completed for each of the times, titrate with the KMnO4, adding only one drop at a time, then recording the findings.

Results

Table 1 Base Line Calculation

Final reading of Pipette

8.5mL

Initial Reading of Pipette

5mL

Base Line (Final-Initial)

3.5 mL KMnO4

Table 2 Uncatalyzed Rate of H2O2 Decomposition2

Final Reading of Pipette

4mL

Initial Reading of Pipette

10mL

Amount of Titrate

6mL

Amount of H2O2spontaneously decomposed

2.5 mL

Percent of H2O2spontaneously decomposed

22%

Table 3 Enzyme-Catalyzed Reaction

KMnO4(mL)

10

30

60

90

120

180

360

Base Line

3.5

3.5

3.5

3.5

3.5

3.5

3.5

Final Reading

8.2

8

7.4

7.4

7

6.8

6.4

Initial Reading

5

5

5

5

5

5

5

Amount of KMnO4Consumed

3.2

3

2.4

2.4

2

1.8

1.4

Amount of H2O2Used

.3

.5

1.1

1.1

1.5

1.7

2.1

Discussion

Once the experiment was conducted, the results were as followed, the amount of H2O2 in the beakers decreased as the amount of time the catalase was in the solution increased. This data proves the hypothesis to be true, and is represented by Table 3, and is validated by the establishment of a base line in Table 1 and Table 2. Tables 2 shows that without the presence of catalase, the H2O2 decomposes slowly, as the amount of H2O2 didn't change dramatically after 24 hours as compared to the base line established on the day of the experiment. However, when the catalase was added, the amount of H2O2 decreased much faster than without the added catalase.

Table 1 Base Line Calculation

Final reading of Pipette

8.5mL

Initial Reading of Pipette

5mL

Base Line (Final-Initial)

3.5 mL KMnO4

Table 2 Uncatalyzed Rate of H2O2 Decomposition2

Final Reading of Pipette

4mL

Initial Reading of Pipette

10mL

Amount of Titrate

6mL

Amount of H2O2spontaneously decomposed

2.5 mL

Percent of H2O2spontaneously decomposed

22%

Table 3 Enzyme-Catalyzed Reaction

KMnO4(mL)

10

30

60

90

120

180

360

Base Line

3.5

3.5

3.5

3.5

3.5

3.5

3.5

Final Reading

8.2

8

7.4

7.4

7

6.8

6.4

Initial Reading

5

5

5

5

5

5

5

Amount of KMnO4Consumed

3.2

3

2.4

2.4

2

1.8

1.4

Amount of H2O2Used

.3

.5

1.1

1.1

1.5

1.7

2.1

Citations

1. Britannica, Encyclopedia. "Catalase". Encyclopedia Britannica, 9 Nov. 2009. Web. 9 Nov. 2009. http://www.britannica.com/EBchecked/topic/99062/catalase

2. College, Board. AP Biology Lab Manual. New York: College Board, 2001. Print.

3. Pack, Phillip E. Cliffs AP AP Biology 3rd Edition. 111 River Street, Hoboken, NJ: Wiley Publishing Inc., 2007. Print.