ENZYME LAB
Safety Instructions
I would make sure that students wrote out the procedure in their own words before
they performed the lab to make sure they understood the directions and asked
questions prior to starting the lab. I would go over the lab a few times before to ensure
understanding and emphasize the importance of safety. Students should make sure to
wear gloves, tie their hair and be cautious with all the equipment. Proper management
should be set up to avoid accidents. Students should be grouped accordingly and given
roles so that each student clearly understands what is expected of them before, during,
and after the experiment if carried out. Students should also be advised of the dangers
of each compound and know how to act in case of an accident.
Introduction: What is a decomposition reaction? What are enzymes? Expand….
A decomposition reaction is a reaction in which a substance degrades into two or more
basic compounds. An example would be the conversion of water (H2O) to hydrogen
(H2) and oxygen (O2).
Enzymes are biomolecules, usually proteins, specialized to act as catalysts in metabolic
reactions.
Purpose: To become familiar with some of the characteristics of enzymes. Expand…..
To catalyze a reaction an enzyme must first bind to a reactant molecule called a
substrate and act on the substrate to generate a product molecule which is then
released.
E + S = E-S = P + E
Materials:
hydrogen peroxide - 3% approx.
copper metal
raw fresh potato
calf liver
MnO2 powder
beaker
hot plates
thermometer
candle, matches
test tubes
mortar and pestle
applicator sticks (splints)
Procedure:
1. Clean 8 large test tubes.
2. Number the test tubes from #1 to #8 and place in a suitable rack.
3. Add approximately 4 mL of hydrogen peroxide to each test tube.
4. Carefully add the following to the test tube and record ALL results:
1.
nothing (do you really need to do this one???)
#2.
a pinch of manganese dioxide- it forms H2o and O2
#3
a small piece of copper- hydrogen peroxide can oxidize copper by
displacing it as copper ions, will dissolve and produce gas
#4.
a piece of liver (10 mm X 10 mm x 10 mm)- oxidizes and precipitates,
bubbles and releases oxygen, produces gas
#5.
crushed liver, the same size as in #4- reaction produced similar to above
#6.
boiled liver (5 min.), same size as in #4- heat denatures or destroys
protein therefore doesn’t react (has denatured catalase proteins that can’t perform
metabolic reaction).
#7.
fresh potatoe, same as in #4- bubbles and foams (oxygen bubbles being
created by catalase)
#8.
A small pinch of catalase (if available)- bubbles consuming hydrogen
peroxide
5. Record the temperature of the hydrogen peroxide before and after adding the pieces
of liver (crushed and raw).
The temperature increases after adding liver (crushed and raw).
6. Repeat #4, adding raw liver and test to determine if the gas evolved is something
you know??? Do a splint test.
The gas that is evolved is oxygen and doing a splint test will show that oxygen is in
fact released.
7. Clean up your equipment, clean our foreign matter from the sinks!!!!!
Discussion Questions
1. Rank the reactions for #1 to #8 using a scale that shows the varying rates of
reactions that you observed. (1 to 5) (A B..F) (none….wild)
12345678-
A
B
B
C
C
A
C
C
2. Is MnO2 an enzyme? Is it a catalyst? How could you prove if it is a catalyst?Manganese dioxide is not an enzyme but it is an inorganic catalyst. It breaks down
hydrogen peroxide (is a catalyst for the reaction). H2O2 usually when left alone
will eventually decompose into oxygen and water but adding manganese dioxide
speeds up the reaction as observed in the experiment. It however does not get used
up in the reaction.
3. Write a balanced equation for the decomposition of hydrogen peroxide.
2 H2O2 (aq)
O2 (g) + 2 H2O (l) + catalase (aq)
4. How could you prove if the enzyme in liver is reusable?
You can do this by adding hydrogen peroxide over the liver and seeing whether a
reaction occurs. If a reaction occurs, the liver is reusable.
5. Try to determine the name of the enzyme in liver cells that is capable of
decomposing hydrogen peroxide.
Catalase
6. What is denaturation? Did it happen in this lab? What are other ways to denature
an enzyme?
Denaturation is when an enzyme is not able to speed up a reaction because it has lost
this property due to environmental conditions. This happened with the boiled liver
because the heat denatured the catalase proteins and metabolic reaction could not be
performed. Enzymes are also sensitive to changes in pH and therefore can also be
denatured if pH levels are altered.
7. Is the reaction exothermic or endothermic? How do you know?
The reaction is exothermic (therefore heat must be released) and this was observed
with the increase in temperature.
8. Prepare a simple procedure that could be followed to show the effect of temperature
on the rate of enzyme activity?
Below is a link to a great activity that can be done with students to show the effect of
temperature on the rate of enzyme activity. Pepsin (protease enzyme found in stomach)
is used to break down an egg white (protein albumen). The albumen is cloudy but
when the pepsin is added at a certain pH and temperature it turns clear meaning the
enzyme has broken down the albumen to smaller molecules. The results showed that
the rate of reaction increased with increasing temperature up to 50 degrees C, which is
the optimum rate of reaction for pepsin. The site provides clear instructions and
guidance for teachers to incorporate into a lesson.
http://www.123helpme.com/view.asp?id=122761
BONUS: What are some applications of enzymes?
Amylases from fungi and plants- catalyze breakdown of starch in flour to sugar
Proteases- biscuit manufacturers use to lower protein level of flour
Trypsin- predigest baby foods
Cellulose- clarify fruit juices
Rennin- cheese manufacturers to hydrolyze protein
Lipases- removal of fatty and oily stains
Catalase- generate oxygen from peroxide to convert latex into foam rubber