Download Enzyme Lab Pre-Lab Background Information: What would happen

Enzyme Lab
Pre-Lab
Background Information:
What would happen to our cells if they made a poisonous chemical? You might think that
they would die. In fact, your cells are always making poisonous chemicals. They do not die
because your cells use enzymes to break down these poisonous chemicals into harmless
substances.
In this lab, you will study the enzyme catalase. This enzyme is found in the cells of many
living tissues. Catalase breaks down hydrogen peroxide (H2O2), a harmful chemical made by your
cells in many normal reactions. If your cells did not use catalase to break down hydrogen peroxide
into water and oxygen, they would be poisoned and die. It might seem strange to use dead cells to
study the function of enzymes. This is possible because when a cell dies, the enzymes remain intact
and active for several weeks, as long as the tissue is kept refrigerated.
Based on what you have read, write the missing chemical formulas into the equation below.
Record in the small parentheses a letter to indicate the state of matter. Balance the equation.
H2O2 (L)
reactant
__________ (__) +
product
__________ (__)
product
Now draw a diagram (geometric shapes) that depicts how catalase breaks down hydrogen peroxide:
List at least 3 facts you know about ALL enzymes: __________________________________
___________________________________________________________________________
________________________________________________________________________________
______________________________________________________________________
Problem: How do changes in temperature affect the activity of the enzyme catalase? How do
changes in pH affect the activity of the enzyme catalase?
Hypothesis: ________________________________________________________________
___________________________________________________________________________
Enzyme Lab
Materials:
 test tube rack with 8 test tubes
 small beaker of hydrogen peroxide
 1 ml pipet
 stirring rod - glass or wood
 liver samples: fresh chunk, fresh chopped, cooked, soaked in vinegar, soaked in bleach
 fresh potato sample
Caution: Do not let the acid, hydrogen peroxide, or bleach (base) come into contact with your
skin. Wear goggles and apron at all times.
Instructions:
Part A - Observation of Normal Catalase Reaction
1. Place a small piece of fresh chunk liver into a test tube. Push it down to the bottom with a
stirring rod.
2. Add 1 ml of hydrogen peroxide to the liver. Observe the bubbles. Much bubbling indicates a very
fast reaction.
3. What gas is being released? ________________
4. In the data chart, record the rate of reaction on a scale of 0 (no reaction) to 5 (very fast).
5. A reaction that absorbs heat is endothermic. A reaction that gives off heat is exothermic. Feel
the temperature of the test tube with your hand.
Has it gotten colder or warmer? ____________________
Is the reaction endothermic or exothermic? ___________________
Part A continued - Is Catalase Reusable?
6. Pour off the liquid from the test tube into a clean test tube.
7. Of what do you think this liquid is composed? __________________________________
8. What do you think will happen if you add hydrogen peroxide to this liquid (no liver present)?
______________________________________________________________
9. Add another 1 ml of fresh hydrogen peroxide to the liquid poured from the first test tube.
Record the reaction rate on the data table.
10. Is catalase reusable? ___________ Justify your answer - _________________________
________________________________________________________________________
Part B - Other Cell Types that Contain Catalase
1. Now test for the presence of catalase in a tissue other than liver. Place a small piece of potato in
a clean test tube. Add 1 ml of hydrogen peroxide. Observe the reaction.
2. Record the rate of reaction on a scale of 0 to 5 on the data table.
3. Does the potato contain catalase? ____________
How can you tell? ________________________________________________________
4. Do you suspect that some cell types contain more catalase than other cell types? _______
How can you tell? ________________________________________________________
Part C - Effect of High Temperature on Catalase Activity
1. Get 1 clean test tube and add a piece of liver that has been boiled. (Boiling brings the liver to a
high temperature, and even if the liver is now cool, it will demonstrate what high temperature
does to the contents of liver cells).
2. Add 1 ml of hydrogen peroxide to the boiled liver. Observe the reaction.
3. Record the rate of the reaction on a scale of 0 to 5 on the data table.
Part D - Effect of Low Temperature on Catalase Activity
1. Obtain a piece of frozen liver from the ice bath on the front table.
2. Add 1 ml of hydrogen peroxide to the frozen liver.
3. Record the rate of reaction on a scale of 0 to 5 on the data table.
Part E - Effect of pH on Catalase Activity
1. Obtain a piece of vinegar-soaked liver from the front desk. Vinegar is an acid.
2. Add 1 ml of hydrogen peroxide to the liver. Observe the reaction.
3. Record the rate of reaction on a scale of 0 to 5 on the data table.
4. Obtain a piece of bleach-soaked liver from the front desk. Bleach is a base.
5. Record the rate of reaction on a scale of 0 to 5 on the data table.
6. What is the effect of low or high pH on catalase activity? ___________________________
_________________________________________________________________________
Part F - Effect of Increased Surface Area on Catalase Activity
1. Place a few pieces of fresh chopped liver in a clean test tube.
2. Add 1 ml of hydrogen peroxide to the liver.
3. Record the rate of reaction on a scale of 0 to 5 on the data table.
4. What is the effect on the reaction if the liver is chopped into small pieces? _____________
________________________________________________________________________
5. How can you explain the results from question 4? ________________________________
________________________________________________________________________
Clean Up:
1. Discard the liquids down the sink.
2. Discard all solids in the garbage can.
3. Clean test tubes and beaker with soapy water. Hang on drying rack to dry.
4. Clean work area.
5. Replace goggles and apron.
6. Wash hands with soapy water.
Data Table 1: Rate of Catalase Reaction with Hydrogen Peroxide
Substance
Part A
Fresh chunk liver
Part A
Reused liver
catalase
Part B
Potato
Part C
High Temperature
(boiled)
Part D
Low Temperature
Part E
Acid (vinegar) liver
Part E
Base (bleach) liver
Part F
Fresh chopped liver
Rate of Reaction
Observations
Analysis:
1. What was the enzyme in this experiment? ___________________________________________
2. What was the substrate? ________________________________________________________
3. Which substance, the liver or the potato appeared to have the most catalase? ______________
What was the proof? ________________________________________________________
4. What is the optimum temperature for catalase activity? ________________________________
5. What is the optimum pH for catalase activity? ________________________________________
6. Under what temperature and pH was catalase least active? _____________________________
7. Explain how an extreme temperature and extreme pH can affect an enzyme. ________________
_____________________________________________________________________________
_____________________________________________________________________________
8. Why was a control needed? ______________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
Conclusions:
1. What are the effects of temperature changes on the catalase activity? _____________________
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
2. What are the effects of pH changes on the catalase activity? _____________________________
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
3. What are the effects of surface area on the catalase activity?
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________