Enzyme Catalysis Formal Lab
OBJECTIVE
Enzymes are proteins produced by living cells; they act as catalysts in biochemical
reactions. A catalyst affects the rate of a chemical reaction. One consequence of enzyme
activity is that that cells can carry out complex chemical activities at relatively low
temperatures. In an enzyme-catalyzed reaction, the substance to be acted upon, the
substrate, binds reversibly to the active site of the enzyme. One result of this temporary
union is the reduction in the energy required to activate the reaction of the substrate
molecule so that the products of the reaction are formed. Each enzyme is specific for a
particular reaction because its amino acid sequence is unique and causes it to have a
unique three-dimensional structure. The active site is the portion of the enzyme that
interacts with the substrate, so that any substance that blocks or changes the shape of the
active site affects the activity of the enzyme. The enzyme used in this lab, catalase, has
four polypeptide chains, each composed of more than 500 amino acids. This enzyme is
ubiquitous in aerobic organisms. One function of catalase within cells is to prevent the
accumulation of toxic levels of hydrogen peroxide formed as a byproduct of metabolic
processes. The objective of this lab is to measure the effects of changes in temperature,
pH, enzyme concentration, and substrate concentration on reaction rates of an enzymecatalyzed reaction in a controlled experiment and to explain how environmental factors
affect the rate of enzyme-catalyzed reactions.
INDEPENDENT
VARIABLES
Amount of enzyme solution (Part A)
Concentration of enzyme solutions (Part B)
Temperature of test tubes (Part C)
pH of enzyme solutions (Part D)
DEPENDENT
VARIABLE
Amount of water and oxygen gas formed by the catalysis of hydrogen peroxide
CONSTANTS
Time (30 second intervals)
Temperature of room
HYPOTHESIS
Based on the knowledge that denaturation of enzymes occurs at extreme temperature and
acidity/basicity, I hypothesize that catalase will be most effective at near-body
temperature and at near-neutral pH levels. In addition, I hypothesize that solutions with
increased enzyme concentration will yield an increased amount of products.
DATA
120
100
80
Full Concentration
3/4 Concentration
60
1/2 Concentration
1/4 Concentration
40
20
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
80
70
60
50
Full Concentration
40
Warm
Cold
30
20
10
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
90
80
70
60
pH5
50
pH6
40
pH7
pH8
30
20
10
0
1
DISCUSSION
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1. The rate of enzyme catalysis decreases as time goes on. The amount of hydrogen and
oxygen gas formed from the catalysis of hydrogen peroxide decreases with each thirtysecond time interval.
2. Increased enzyme concentration correlates to increased enzyme activity. As seen in the
data, the greatest amount of hydrogen and oxygen are formed when the concentration of
enzyme is highest; likewise, the least amount of hydrogen and oxygen are formed when
the concentration of enzyme is the lowest.
3. Enzyme activity was higher at 37-degrees Celsius than at 10-degrees Celsius. This can
be attributed to the fact that enzymes function most efficiently at near-body temperature.
4. Enzyme activity was greatest at neutral pH. With increases or decreases in pH resulted
consistent decreases in enzyme activity.
5. A buffer is a substance that maintains pH in solutions by donating hydrogen ions when
they are depleted and accepting them when they are in excess. The use of a buffer in parts
A, B and C would have ensured acidic neutrality in experimentation and thus may have
led to increased enzyme activity.
6. The general conditions necessary for effective enzyme action are high concentration of
enzyme, near-body temperature and near-pH neutrality. These conditions differ for
individual enzymes, however.
7. The same procedures would be followed with the subtraction of the disks soaked with
catalase. After observing catalysis without the presence of enzymes, one could find the
difference in the amount of hydrogen and oxygen produced with and without enzymes in
order to show how much faster hydrogen peroxide decomposes in the presence of
catalase.
8. Enzymes remain active even after the death of a cell as long as they are chilled. As long
as the catalase does not denature, it will still be able to catalyze hydrogen peroxide.
CONCLUSION
The objective of this lab was to measure the effects of changes in temperature, pH,
enzyme concentration, and substrate concentration on reaction rates of an enzymecatalyzed reaction in a controlled experiment and to explain how environmental factors
affect the rate of enzyme-catalyzed reactions. We experimented on enzyme concentration
in Part B, on environment temperature in Part C and on environmental pH in Part D. My
hypothesis, that catalase will be most effective at near-body temperature and at nearneutral pH levels, was half correct. Catalase had increased enzyme activity not at neutral
pH levels but at slightly acidic pH levels. However, it did have the greatest catalysis rates
at near-body temperature. In addition, my hypothesis that increased enzyme
concentration would yield a great amount of products was also correct. This lab allowed
me to observe first-hand how enzymes in living organisms can help to speed up chemical
reactions that are necessary for life. In a broader context, this lab relates to the study of
metabolism, which is the set of chemical reactions that occur in living organisms to
sustain life.
ERROR ANALYSIS
My group was responsible for testing catalase at pH6 and pH8. Before we began timing,
some catalase had begun to react with the hydrogen peroxide in both instances. This may
have distorted the accuracy of our results.