Enzyme Catalysis

Purpose  

The purpose of this enzyme catalysis lab was to understand the observe the conversion of hydrogen peroxide to water and oxygen gas by the enzyme catalase.The outcome of changes in PH,temperature, and enzyme concentration. Also, how environmental factors affects the rates of enzyme-catalyzed reactions.

Introduction

Enzymes are a very important part of cell activity and survival. Enzymes are proteins that act as catalysts, which means they speed up chemical reactions. All enzymes have a specific active site made up of certain amino acids that only certain kinds of substrates, molecules, can go into. When an enzyme is denatured it changes the shape of the active site making it no longer able to turn the substrates into the product needed for the cell. There are many things that can denature an enzyme. Some of the ones we tested out in this lab were temperature and pH level.

Methods

2B    We add 10 mL of 1.5% H2O2 in each clean plastic cup, add 1 ml of H2O then add 10 mL H2SO4(1.0M) with a syringe. We mix the solution well  then removed a 5-mL sample. Using a burette to add KMnO4 a drop at a time, to the solution until pink or brown color is obtained. Before we started using the burette we got the initial and at the end the final reading.

  

2C  The 1.5% H2O2 (about 15 mL) in a beaker was stored and  not covered at room temperature for about 24hrs. We repeated steps 2-5 from 2B to establish the proportional amount of H2O2 left.

2DWe add10 mL of 1.5% H2O2 in each clean plastic cup then added 1mL of Catalase extract (yeast) into a syringe. Next, we took the 10 seconds cup and the syringe that was filled with yeast and added it. We had set a timer swirl gently for 10 seconds. At the 10 seconds we added 10 mL H2SO4 (1.0M). We had repeated those steps for 30, 60, 90,120,180 and 360 seconds. Using a burette to add KMnO4 a drop at a time, to the solution until pink or brown color is obtained. Before we started using the burette we got the initial and at the end the final reading.   

measured out the H2O2

add 1 mL of Catalase extract

solution going to zero mark line

  removed  5 mL

Using the Brunette to add KMnO4, a drop at a time until the solution is pink or brown

one of the solution turned  brown 

Part 2B: Baseline

Final reading of burette	34.2 mL
Initial reading of burette	31 mL
Base line	3.2 mL KMn02

Part 2C:

Part 2D:

KMn04(mL)	10s	30s	60s	90s	120s	180s	360s
Base Line	3.2	3.2	3.2	3.2	3.2	3.2	3.2
Final Reading	37.4	34.9	49.2	42.2	39.9	37.6	35.5
Initial Reading	34.9	31.6	46.8	39.9	37.6	35.5	37.5
Amount of KMn04 Consumed	2.5	3.3	2.4	2.3	2.3	2.1	2
Amount of H202 Used	.7	-.1	.8	.9	.9	1.1	1.2

 

Discussion: The base line (2B) of 3.2 mL indicates the amount of hydrogen peroxide present in a 10 mL (1.5%) hydrogen peroxide mixed with 1 mL of water and 10mL of sulfuric acid. Through titration, the baseline required 3.2 mL of potassium permanganate. The baseline serves as a comparison for the rest of the lab experiments. It's crucial to recognize the proportional relationship between potassium permanganate and hydrogen peroxide. 2 molecules of potassium permanganate react with 5 molecules of hydrogen peroxide. We noticed that when hydrogen peroxide was present with catalase it formed bubbles, the mixture became cloudy, and oxygen was produced. Adding sulfuric acid would halt this reaction because the enzyme catalase would become denatured from such a rapid change in ph. Exercise 2C, helped us determine the rate of decomposition that hydrogen peroxide experiences in 24 hours. This process was spontaneous since hydrogen peroxide is broken down into oxygen and water, which indicates that no energy input is required. In 2C, we used only .3 mL of potassium permanganate to titrate the solution. The results demonstrated that only 10% of the hydrogen peroxide decomposed in 24 hours without the use of an enzyme. The natural decomposition of hydrogen peroxide will be slower than decomposition of hydrogen peroxide with enzymes. Errors could occur during titration, which might have resulted in skewed data. For example, too much potassium permanganate could have been used to make the solution pink or brown. Some of the titrations we completed were darker shades of pink and brown than other titrations we completed. Also, the titrating device leaked a little from the handle, which could have altered the readings on the burette. In experiment 2D, we repeated the same steps for the base line but we waited for different time intervals before adding the sulfuric acid. Our results demonstrated that as the time intervals increased in length, the amount of potassium permanganate required to change the solution’s color decreased. This occurs because the solution had more time to react and break down hydrogen peroxide into its components. Having the enzyme boosts the speed of this reaction. As time went up, the amount of potassium permanganate titrated decreased, and the amount of Hydrogen peroxide used increased. The variable we controlled was the amount of time the catalase was allowed to function before the addition of sulfuric acid. As a result, the amounts of hydrogen peroxide used up in the reaction changed. The highest reaction rate occurred during the first 10 seconds because we added only a certain amount of catalase into the solution and the concentration of this enzyme remained high during this short period of time. The amount of hydrogen peroxide readily available is extremely high since there are very few products. The lowest rate occurred during the 360 second time interval because the amount of hydrogen peroxide products is extremely high compared to the amount of hydrogen peroxide available. This means that the catalase has very few hydrogen peroxide molecules to react with. Sulfuric acid has an extremely high concentration of H+ ions, which indicates that this acid has an extremely low pH level. Enzymes optimal pH range is 6-8, so when sulfuric acid is added the enzyme is denatured. Lowering the temperature of the solution’s environment would slow the reaction down. If the temperature continues to decrease, then the reaction would eventually stop. Most enzymes are synthesized to function in body temperature. To test the effects of low ph levels, we could add hydrochloric acid. For neutral pH levels, we could add distilled water. For high pH levels, we could potassium hydroxide.

Conclusion

After changing the pH level of the environment of the enzyme, the predicted outcome was correct. We predicted that when you change the pH level of the enzyme's environment that it will decrease activity of the enzyme, producing less product. Through our charts and graph we were able to prove this. As there was less hydrogen peroxide, there was more enzyme activity due to the environment becoming more favorable. In our experiment we showed how enzymes must have a certain environment to preform to their full capacity.