Download LabEnzymes

Biology
Lab
Name___________________
Date___________Hour_____
Enzymes
Introduction:
“Enzymes are biological molecules that catalyze (speed up) chemical reactions. You could call enzymes the
“Builders and Do-ers” in the cell; without them, life could not occur. Every cell makes hundreds of different
enzymes to carry out the reactions necessary for life. Fortunately for the cell, enzymes are not used up when
they catalyze a reaction, but can be used over and over.
The DNA in each cell encodes all the information needed to make its many different enzymes. Enzymes are
relatively large molecules of protein. They are produced whenever the cell “senses” a need for that particular
enzyme; that is, whenever a job needs to be done in the cell which only that enzyme can do.
The molecule or molecules on which an enzyme acts is called its substrate. Enzymes are said to be very
“specific” meaning that they recognize only one substrate (or a few closely related substrates) and convert it into
a specific product. You could say that each enzyme can do only one type of job. Each enzyme is specific
because it is folded into a particular three-dimensional shape. Within the folds of each enzyme is the active
site, the place where the substrate fits and where the chemical reaction takes place.
Enzymes work very quickly, often catalyzing thousands of reactions per minute. The rate at which an
enzyme works is influenced by many factors including temperature and pH. Enzymes have a temperature and a
pH at which they work best, and if an enzyme is exposed to extremes of heat or pH it will not work at all. The
interactions that hold the protein in its particular shape become disrupted under these conditions, and the 3dimensional structure unfolds. In this case, the enzyme is said to be denatured. Other important factors that
influence enzyme activity are the concentration of substrate and the concentration of enzyme. Up to a point, the
more substrate that is present, the faster the reaction. However, when the substrate concentration is so high
that an enzyme is working as fast as it can, further increases of substrate concentration will have no effect on
the rate of product formation.” (2000 CIBT)
Hydrogen peroxide (H2O2) is a poisonous byproduct of your body’s metabolic processes. Hydrogen peroxide
can damage cells if it is not removed. Catalase is an enzyme that speeds up the breakdown of hydrogen
peroxide into water (H2O) and oxygen gas (O2). Your cells and other organisms’ cells contain the enzyme
catalase. For this lab, we will use yeast cells as our source of catalase. The chemical equation for this reaction
is shown below.
Catalase
2 H2O2 ---------------→ 2 H2O + O2
Observations: Watch the teacher demo the experiment and answer the following questions.
1. What is the enzyme used in this lab?
2. What is the substrate used in this lab?
3. Describe what happens when the enzyme coated disk is placed in the substrate.
4. Explain what causes the disk to move.
Prediction: As you decrease the concentration of hydrogen peroxide (substrate), what will happen to the time
it takes for the reaction to be complete?
Hypothesis: Form the prediction you wrote above into a hypothesis (If…then… statement).
Materials:
1 Catalase Solution
Stirring Rod
Forceps
Filter paper disks
Hydrogen peroxide (2%, 1.5%, 1%, 0.8%, 0%)
50 mL beaker
Graduated cylinder
Stopwatch
Procedure:
1. Place goggles on eyes. Do not remove goggles until you are cleaned up and the teacher has inspected
your lab table.
2. Pour 30 mL of 2% H2O2 into a clean beaker.
3. Pick up a paper disk with clean forceps. Using the forceps, dunk the disk in the enzyme solution, until
the disk is uniformly moistened.
4. Drain the disk on a piece of dry paper towel and blot excess enzyme from the disk.
5. Place the disk on the end of a glass stirring rod. Push the disk to the bottom of the reaction beaker
containing H2O2 and start timing.
6. Stop timing when the disk reaches the top of the beaker. Record the time in seconds for each trial on
Table 1.
7. Remove the disk and discard it into the trash.
8. Wash and dry the reaction beaker.
9. Repeat steps 2-8 for each of the other substrate concentrations (1.5%, 1%, 0.8% & 0%).
10. Return materials to lab bin. Wash and dry table. Have your table inspected by the teacher. After your
table has been approved, return your goggles to the goggle cabinet.
Data:
Table 1: Catalase Activity with 2%, 1.5%, 1%, 0.8% and 0% H2O2
Concentration Time for disc
Class
of Substrate
to rise
Average
(%)
(s)
Time (s)
2%
1.5%
1%
0.8%
0%
Analysis:
In Table 1, record the class average time it took for the disk to rise at each of the enzyme concentrations.
Graph class average time (y-axis) vs. substrate concentration (x-axis). The graph should have a title and each
axis should be labeled with units. Be sure to have a continuous scale on each axis. Draw the best fit line for the
graph.
Conclusion: Answer the following questions in complete sentences on a separate sheet of paper.
1. How do you know if the enzyme is working efficiently?
2. Do you accept or reject your hypothesis (see page 1 of the lab)? Explain your answer using actual data
to back up your answer (Start your answer with “I accept or reject my hypothesis because…”).
3. Explain why varying the concentration of substrate influenced the time it took for the reaction to occur.
4. A biology student repeated the lab except this time she varied the pH instead of the substrate
concentration. Examine her data below. Explain what her data shows.
pH of Solution
2
4
7
8
10
Class Average Time (s)
27
9
7
18
33
5. What does denature mean?
6. What would happen if the yeast solution was boiled before using it in this lab? Explain your answer.