Download Characteristics of Enzymes Lab

Characteristics of Enzymes Lab
Introduction: In this lab, some of the characteristics of enzymes will
be investigated by addressing four questions that allow you to make
observations, analyze results and draw conclusions about the
behavior of enzymes.
Enzymes have five important properties that you should know:
1. They are always proteins.
2. They are specific in their action. Each enzyme controls one particular reaction, or type of
reaction. Thus sucrase degrades sucrose and only sucrose (table sugar).
3. They are not altered by the reaction. This means that an enzyme can be used repeatedly.
It also means that enzymes appear neither in the reactants nor in the products of a
chemical equation.
4. They are destroyed by heat. This is because enzymes are proteins, and all proteins are
destroyed by heat. Destruction of protein by heat (or under any extreme conditions of pH
or salt concentration) is called denaturation.
5. They are sensitive to pH. The term pH refers to the degree of acidity and alkalinity of a
solution. Most intracellular enzymes work best in neutral conditions, i.e. conditions that are
neither acidic nor alkaline.
In this experiment you will investigate the action of catalase, from a
small piece of beef liver, on hydrogen peroxide, under varying
conditions.
BACKGROUND
Metabolism is the sum total of chemical reactions in the body
that are necessary to the maintenance of life. Enzymes are
biological catalysts that can speed up, and control, chemical reactions that would otherwise
virtually never occur at normal body temperature, 37°C. Thousands of
chemical reactions are occurring in the human body every moment of
life, and each of these reactions is controlled by a particular enzyme.
Enzymes are extremely efficient. Some of the chemical reactions
that take place in the body produce toxic by-products, which must be
quickly degraded or converted. For example, certain reactions in the
liver produce hydrogen peroxide, which is extremely poisonous. Under
the influence of an enzyme called catalase, the hydrogen peroxide is
broken down into water and oxygen. Catalase acts quickly; one molecule of it can deal
with six million molecules of hydrogen peroxide in one minute. This same reaction can be
catalyzed by iron. However, to achieve the same speed there would need to be about six
tons of iron.
The reaction we will investigate in this lab is that of the decomposition of hydrogen
peroxide (H2O2). H2O2 breaks down into H2O and O2 and that the release of the O2 formed
bubbles. This compound is formed in cells and is poisonous to them. Therefore, it must be
decomposed as rapidly as possible. An enzyme called catalase speeds up this process in our
cells.
Catalase
The 4 questions/problems that will be investigated are:
1. What things can act as catalysts?
2. Are catalysts reusable?
3. What is the effect of temperature on enzymes?
4. What is the effect of pH on enzymes?
Materials
3% H2O2
pH paper
ice
beakers
MnO2
Potato
Sand
catalase
test tubes
test tube rack
test tube holders
hot plate
1M NaOH
1M HCl
marking pencils
Investigation 1: What things can act as catalysts?
Procedure
1. Mark 4 tests tubes #1, 2, 3, 4.
2. Pour 10 drops of 3% hydrogen peroxide into each of the test tubes.
3. Be prepared to observe the reaction rate (on a scale of 0-5, 0=none, 5=fastest) as the
materials below are added to the H2O2. A fast reaction will have a lot of bubbles.
Test Tube #1: Add a pinch of fine sand.
Test Tube #2: Add a pinch of manganese dioxide.
Test Tube #3: Add a small piece of potato.
Test Tube #4: Add a drop of catalase.
4. Record the data in the table provided.
5. Respond to the problem statement using your data to support your conclusion.
6. Clean the test tubes but do not wash off the numbers. They will be reused.
Sample
H2O2 + Sand
H2O2 + MnO2
H2O2 + Potato
H2O2 + Catalase
0
1
Table of Reaction Rate
2
3
4
5
Other Observations
Investigation 2: Are catalysts reusable?
Procedure
1. Add 20 drops of catalase to a test tube and then add 10 drops of H2O2.
2. Observe the rate of reaction.
3. Allow the tube to stand until no more bubbles form.
Question: Based on your previous knowledge, what liquid should remain in the
test tube at the end of this reaction?
4. Once the reaction has stopped, add 10 more drops of H2O2.
5. Observe and record.
6. Respond to the problem statement using your observations to support your
conclusion.
Investigation 3: What is the effect of temperature on enzyme activity?
Procedure
1. Use the test tubes from Investigation 1.
2. Place 20 drops of catalase in each of the test tubes and prepare each of the tubes as
follows:
Tube 1: Chill in ice water bath.
Tube 2: Leave in test tube rack at room temperature.
Tube 3: Warm to body temperature by holding in cupped hand.
Tube 4: Place in boiling water.
3. When each test tube has been in it’s temperature zone for 10 minutes, place them in
the rack and add 10 drops of H2O2 to each tube.
4. Record the rate of reaction using the same scale as in Investigation 1.
Rate of Reaction
Tube 1: ____________________
Tube 2: ____________________
Tube 3: ____________________
Tube 4: ____________________
5. Use your results to respond to the problem statement.
6. Clean the test tubes for use in the next investigation.
Investigation 4: What is the effect of pH on enzymes activity?
Procedure
1. Place 10 drops of H2O2 in each of 3 numbered test tubes.
2. Add the following to the tubes:
Tube 1: add 1 drop of HCl.
Tube 2: add 1 drop of H2O.
Tube 3: add 1 drop of NaOH.
3. Measure and record the pH of the solution in each tube.
4. Add 20 drops of catalase to each test tube and record the reaction rate in the chart
provided using the same scale used in Investigations A and C.
Acid
Base
Neutral
Reaction Rate
Tube 1
Tube 2
Tube 3
Final Write Up
1. The primary reaction catalyzed by catalase is the decomposition of hydrogen peroxide
to form water and oxygen, which occurs spontaneously, but not at a very rapid rate.
Write a balanced equation for this reaction. (Remember that catalase is not a reactant
or a product and can be written over the arrow).
Presentation of Data
2. Make new data tables for all 4 parts.
3. Make a bar graph of the results of Parts 1, 3, and 4. Each graph must have a title and
be appropriately labeled.
Conclusion
4. In paragraph form, discuss four characteristics of enzymes evident from this lab.
 Be sure to respond to the questions in the background section.
 Be sure to use the results of each investigation to support your conclusions
about the properties of enzymes and to address any questions that were part of
the investigations.
 Use no personal pronouns.
 Use your previous knowledge and your text as a resource.
 Be thorough but concise.
 Use key terminology where appropriate.
Validity
5. Discuss the validity of these investigations and any suggested improvements to
address possible errors in your procedures.