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AP Lab 2

Completing the Research Notebook for AP Biology Lab #2.....Enzyme Catalysis

Resource: Lab Two, Enzyme Catalysis

Page 19 of the AP Biology Lab Manual

 

Part 1: Title (Write the title in the form of a question after you have completed the pre-lab)

 

Part 2: Objectives:

The two main objectives are presented in the Overview on the first page of the lab handout (page 19)

 

Part 3: Prelab Questions and Answers:

Note: You will need to read the Introduction on pages 19-22 of the lab handout carefully.

1. What is a very important role that enzymes have in cells?

2. Explain the participants in an “enzyme catalyzed reaction” and explain the “active site” of the enzyme.

3. The following are factors that affect an enzyme’s action. For each, explain its effect and why it has this effect.

a. salt concentration b. pH c. temperature d. activators and inhibitors.

4. Write the equation for the decomposition of hydrogen peroxide. Briefly describe catalase and its role in living

cells.

5. Read pg 21 and examine Figure 2.1 carefully. Then, explain “initial rate” and how to calculate the rate of the

reaction using the graph.

6. There are many ways to study the rate of a chemical reaction. How will the rate of the reaction in this laboratory

be measured?

7. Read the general procedure, and then copy Figure 2.2 which is a visual of this procedure.

8. “Assay” means measure, and a titration will be done to measure the amount of hydrogen peroxide remaining in

the beaker. Copy the equation on page 22 which is the titration reaction.

9. The titration:

a. What goes in the buret?___

b. What reactant in the beaker will react with the titrant?_____

c. Once all of the reactant is used, excess titrant added will cause the solution to turn _________. This is the

e_______ of the reaction.

10. This is a timed experiment. What is added to stop the enzyme reaction when the time is up? How does this

work? (see #2 on page 22, general procedure)

 

Parts 4 and 5: Method and Data Tables.

(Note: The method and tables will be presented together.)

Exercise 2A Test of Catalase Activity

For this part, get a ruler and make a chart as shown here:

Procedure Qualitative Data

Mix 10 mL 1.5 % H2O2 and 1mL catalase

Place 5 mL of catalase in test tube and

place in boiling water bath for 5 min; then

mix 10 mL of 1.5 % H2O2 with this boiled

catalase

Macerate small piece of potato and

mix it with 10 mL of 1.5% H2O2

Exercise 2B The Base Line Assay

The following will be placed in a 50 mL beaker: 10 mL of 1.5 %H2O2 , 1 mL H2O, and 10 mL H2SO4. KMnO4 will

be used to titrate this solution to its endpoint. (Note: this is a baseline to determine how much H2O2 is initially

present; WATER will be added instead of CATALASE for this baseline assay.

(Now copy the Base line calculation table from page 24)

Exercise 2C The Uncatalyzed Rate of H2O2 Decomposition

A small quantity of the 1.5 % H2O2 will be placed in a beaker and stored uncovered for 24 hrs. The baseline assay

steps will be completed to determine the percent of H2O2 that spontaneously decomposed.

(Now copy the Uncatalyzed H2O2 decomposition box)

Exercise 2D An Enzyme Catalyzed Rate of H2O2 Decomposition

A 10 mL sample of the 1.5% H2O2 will be mixed with 1 mL of the catalase, and the reaction will be stopped with

sulfuric acid at these time intervals: 10, 30,60,90,120,180 and 360 seconds. A titration will be done for each

solution to determine the amount of H2O2 remaining after the reaction was stopped. Note: each titration will be

done using ONLY 5 mL of the solution from the timed experiment.

(Now copy table 2.1 on page 26)

 

Post Lab:

Part 6: Questions and Answer Section

Exercise 2A Questions and Answers

(see page 23 of lab handout)

Exercise 2B (no questions)

Exercise 2C (no questions)

Exercise 2D

 

Part 7: Graph.

The amount of H2O2 remaining was dependent on time.

Graph the data

Y axis = dependent = H2O2 decomposed (mL)

X axis = time = seconds

Hints to answers to questions: (page 28)

1. Show work clearly for one rate calculation, then you can complete the chart using your calculator. Make sure

the chart is clearly drawn and complete.

rate units: mL / sec

2. Go back to the introduction and use the discussion on initial rates for explanation.

3. Same for this question.

Things to think about.

When substrate and enzyme are initially mixed, all active sites are occupied and the rate is high. As time passes,

and substrate is decomposed, wouldn’t it be harder for the

E-S complex to form? Why? What would happen to the graph shape? What has happened to the rate?

4. Refer to introduction and text info on the effect of pH on enzyme reactions.

5. This question involves a knowledge of molecular collisions. In order for a reaction to proceed, molecules (in this

case enzyme and substrate) must collide with sufficient kinetic energy and in the proper orientation. Think about

lowering temperature. What does lowering temperature do to molecular motion???

6. Experiment Design:

Choose ONE variable from the list.

Your design should include the following outline:

Hypothesis:

Basic set up and procedure:

Experimental variable:

Controls:

What quantitative measurements will be taken to graph:

How many times would you do the experiment?

What results would you expect?

 

Part 8: Theme Correlation: Structure fits Function, Regulation of Enzymes

 

Part 9: Conclusion/Discussion

1. Explain how an enzyme works using H2O2 and catalase as substrate and enzyme.

2. What does the data indicate with regard to non catalyzed decomposition of H2O2 ?

3. What does the data indicate with regard to rate of enzyme reactions over time? Be sure to use “initial rate” in

your explanation.

4. What data was collected that can show the effect of environmental factors on enzyme reactions?

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