Jimenez, ChristianAP Biology; P.111-09-09Mrs. Gonzalez

Title: Enzyme CatalysisPurpose: The purpose of this activity is to determine the rate for the enzyme catalyzed decomposition of hydrogen peroxide.

Hypothesis: I predict that the reaction will begin rather quickly with the addition of the enzyme, but will slow as the H2O2 is converted to H2O and O2.

Background: Enzymes are basically proteins that serve as biological catalysts in reactions. In other words they speed up reactions. The enzyme works on a so called substrate which fits into a mold in the enzyme called the active sight. There, reactions take place as the enzymes lower the necessary activation energy. The substrate independently departs and the enzyme is left to be reused over and over again. Enzymes provide the necessary speed boost that most of our internal reactions require (e.g. Digestive Enzymes, etc) and without them, human life would be impossible.

Procedures: Described in the lab manual

Materials: Listed in the lab manual

Data:Titration Syringe

Initial Reading 10

Final Reading 6.6

Baseline 3.4

Time (seconds)

10 30 60 120 180Baseline Volume 3.4 3.4 3.4 3.4 3.4

Initial Volume 10 10 10 10 10

Final Volume 7.5 8.4 9.0 9.7 9.9

Amount of KmnO4 Used (Initial – Final)

2.5 1.6 1 0.3 0.1

Amount of H2O2 used (baseline- KmnO4 used)

0.9 1.8 2.4 3.1 3.3

Time Interval (seconds)

Initial 0 to 10 10 to 30 30 to 60 60 to 120 120 to 180

Rates .9 1.8 2.4 3.1 3.3

Conclusion:

1. What is the purpose of this activity? The purpose of this activity is to determine the rate for the enzyme catalyzed decomposition of hydrogen peroxide.

2. What is the i.v. in this activity? d.v.? some (four) constants? The independent variable is the amount of time allowed to catalyze. The dependent variable is the amount of H202 left. Constants are the temperature of the Kmn04, the amount of H202 that was started with, the setting of the experiment and the temperature of the H202.

3. What is an enzyme? Substrate? Induced fit? An enzyme is a protein that serves as biological catalyst that speeds up reactions. They allow reactions to occur with the minimum activation energy needed. A substrate is any molecule acted on by an enzyme for the reaction to occur. Induced fit is the slight changing of the active site when the substrate is introduced to it to better accommodate the substrate.

4. In this activity, what is the enzyme? The substrate? The product? The enzyme is catalase. The substrate is H2O2. Product is H2O and O2.

5. How could you show that oxygen gas evolved (formed) in the reaction? You could show that oxygen formed because if you light a match and placed it in a bag it would blow up. OR if you let the reaction happen inside a bag you will notice how the bag will inflate and possibly explode do the oxygen.

6. What are some factors that affect the rate of enzyme catalyzed reactions? ( p. 19-20). Describe each one in detail. Some factors that affect the rate of the reactions is PH because it either causes the enzyme side groups to gain or lose H+ denaturing the enzyme. The salt concentration because if it is too high or too low it interacts with the side groups denaturing the enzyme. Temperature because over energizes the bonds past the optimum level denaturing the enzyme. And activators and inhibitors because they can unfold the enzyme reduce the disulphide bridges, or by reacting with the side chains either blocking them or changing them.

7. What is the function of potassium permanganate in this activity? What is titration? The function of potassium permanganate (the titrant) is to measure how much H2O2 is left. Titration is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of a known reactant.

8. What reaction would you expect if you added boiled catalase to hydrogen peroxide? Explain your answer. I would not expect anything to happen because the enzymes in the boiled catalase are already denatured therefore no reaction can occur.

9. If you boiled a piece of potato or liver, and added hydrogen peroxide, what reaction would you expect? Explain why. I would expect no reaction because boiling denatures the enzymes and when they are denatured no reaction can occur.

10. In this activity, when is the rate the highest? Explain why. The rate is the highest at the beggining because the concentration of substrate is the highest at the start; the catalase is fresh and accepts as many substrates (H₂O₂) as possible into its active sites. This makes up for the exceptionally high rate of reaction.

11. When is the rate slowest? For what reason is the rate slow? Eventually, after the initial high rate the enzyme becomes saturated with substrates, and cannot continue to increase its rate of catalysis, so therefore cannot increase. As less substrate molecules become available, reaction rate slows down until it eventually levels off or reaches 0, when all substrate sources are depleted. This is when the rate is lowest, near the end of the reaction; in this case it’s supposed to be from 120 to 180 seconds.

12. Explain the inhibiting effect of sulfuric acid on the function of catalase. Relate this to enzyme structure and chemistry. The inhibiting effect of sulfuric acid (H₂SO₄) is mainly because it lowers the pH of the enzyme. Sulfuric acid is a very strong acid, so it denatures the protein. If the pH is lowered, the side chains will begin picking up hydrogen ions from its environment, which might disrupt its conformation, ultimately inhibiting its function. The secondary and tertiary structures of the enzyme become altered, thus changing the behavior of the enzyme. In other words, the substrate may not fit or the side chains will not interact correctly because of the hydrogen added by the sulfuric acid.

13. Predict the effect lowering the temperature would have on the rate of enzyme activity. Explain your prediction. Lowering the temperature will have a negative effect on an enzyme, since kinetic energy is needed to start the reaction. If it becomes too cold, the enzyme will denature and it will no longer function properly.

14. Different enzymes work better under different conditions. Where in a human body might it be beneficial to have enzymes that work well in acidic environments? In the stomach.

15. There is a large amount of catalase in the human liver. Does the liver break down more hydrogen peroxide in the summer or winter? Explain your answer. Neither, because the body will always be in homeostasis and therefore external temperatures will not affect your internal and less the enzyme.

16. Of the thousands of enzymes known, there is a family of enzymes called proteases that catalyze a reaction breaking down proteins. What do you think would happen if you added a protease to your sample of catalase before proceeding with your experiment? A reaction would occur between protease which acts upon proteins and catalase which is a protein. The reaction would most likely have caused the catalase in the experiment to denature and that would have made it not break down the H2O2.

17. Summary- at least 15 lines typed, 20 handwritten.Enzymes are biological catalysts that speed up reactions necessary to live. There are different types of enzymes for different types of reactions. Each enzymes specificity is determined by the shape of its active sight and clearly represents the induced fit how a substrate perfectly binds to the active sight only with a slight change of the enzyme. Substrates or molecules that require a speedier reaction are introduced to the active sight of the enzyme where after a certain amount of time the products are released and the enzyme may be used over and over again. This lab was helpful in showing us how enzyme catalysis really happens in biology. I believe we went wrong in establishing our baseline; we messed up quite a few times and these erroneous trials may have been corrected with a repetition of the lab itself; however, time did not allow us to do so. My hypothesis was partially correct as the reaction most certainly did begin quickly and slow as the time moved on, but I was essentially incorrect in the idea that enough H2O2 would remain so that the KMnO4 would react. Either way, the lab represented success in the fact that it taught me an essential concept to understanding how enzymes work. Reactants have an energy barrier called the activation energy which must be surpassed and enzymes serve as a helper to fulfill that energy goal quicker.