Enzymes in Action Lab

Enzymes in Action

Problem: Are there enzymes in your cells that react with dangerous chemicals in your cells?

Introduction: There are thousands of different types of enzymes found in our body. Enzymes are composed of proteins, which are composed of polymers made of long chains of amino acids.

Cells in your body are continually making dangerous chemicals that have to be destroyed in order to keep your cells functioning properly. The enzymes in your cell break down these dangerous chemicals into harmless chemicals in order to keep your cells safe. One such enzyme is called catalase, its job is to speed up the reaction to break down hydrogen peroxide (H₂O₂) in your cells. It breaks down hydrogen peroxide into harmless chemicals for your body: water and oxygen.

Hydrogen peroxide is created by normal cell processes as a byproduct from chemical reactions. However, if this hydrogen peroxide is not broken down, the cell would be poisoned and die.  You will be looking at catalase enzymes in chicken liver cells.  These cells are no longer alive, but the enzymes are still intact and able to survive as long as they are refrigerated.

Part A: Normal Catalase Reaction

Steps:

1. Add 2 mL of water to 1^st test tube. Add a small cube of liver and record your observations in data table. Feel the test tube for any temperature change.

2. Add 2 mL of hydrogen peroxide to 2^nd test tube. Add a second cube of liver and record your observations. Feel the test tube for any temperature change.

3. Add 2 mL of hydrogen peroxide to 3^rd test tube. Take a cube of liver and mash it up with a fork and add to test tube. Record your observations and feel the test for any temperature changes.

Data:

Size and condition of liver	Experimental Liquid	Observations	Rate of reaction 0-5: 0=no reaction, 1= slow, 5=very fast
1 cm cube chicken liver	2 mL H2O
1 cm cube chicken liver	2 mL H2O2
1 cm cube chicken liver (mashed)	2 mL H2O2

Questions:

1. What is the purpose of putting the liver in water? Why is this a necessary step?

2. Describe the difference between the whole cube of liver and the mashed up cube of liver? What could account for the difference in the two reactions?

3. Is the reaction that occurred exothermic or endothermic? Explain why.

4. Balance the equation that occurs that breaks down the hydrogen peroxide. Identify the reactants and products by name.

H₂O₂ àH₂O + O₂

Part B: Second catalase reaction

Steps:

1. Pour off the remaining liquid from your liver cube from test tube #2 into a fourth test tube.

2. Add a new piece of liver to this liquid. Write your observations.

3. Add 2 mL of hydrogen peroxide to the liver cube in test tube #2 and record observations.

Questions:

1. Identify by name what is the remaining liquid that you poured into the test tube.

2. Describe your observations after the liver was added and rate the reaction rate from 0-5.

3. Describe your observations after the hydrogen peroxide was added to test tube #2. Rate the reaction rate from 0-5.

4. Is the catalase enzyme in your cells reusable? What is your evidence?

Part C: What tissues contain catalase?

Steps:

1. Dump the liver into the trash bowls by the sinks. Make sure NO liver is dumped into the sink. Wash out your test tubes and return to the test tube rack.

2. Add 2 mL of hydrogen peroxide to each to three test tubes.

3. Add to test tube #1 a small piece of potato, to test tube #2 a small piece of apple, to test tube #3 a small piece of beef. Record your observations. Place all samples in trash bowl and wash out test tubes.

Questions:

1. Rate the reactions of the three substances from 0-5 for reaction rate:

Potato: _____________

Apple: _____________

Beef: ___________

2. Based on your observations, which tissues contain catalase?

3. Do some tissues contain more catalase than others? How can you tell?

Part D: What Is the Effect of Temperature on Catalase?

Steps: Hot water bath

1. Put a piece of liver into the bottom of a clean test tube and cover it with a small amount of water.

2. Place this test tube in a boiling water bath for 5 minutes. (Use a test tube holder for hot test tubes!)

3. Remove the test tube from the hot water bath, allow it to air cool, then our out the water.

4. Add 2 mL of hydrogen peroxide.

Steps: Warm and ice water bath

1. Put equal quantities of liver into 2 clean test tubes and 1 mL of H₂O₂ into to two other test tubes.

2. Put one test tube of liver and one of H₂O₂ into an ice bath. Place the other set in a warm water bath (not boiling).

3. After 3 minutes, pour each tube of H₂O₂ into the corresponding tube of liver (pour cold H₂O₂ into cold liver and warm H₂O₂ into warm liver) and observe the reaction.

Questions:
1. What was the reaction rate for the boiled liver and hydrogen peroxide?

2. What is the reaction rate for the cold liver/peroxide?

3. What is the reaction rate for the warm liver/peroxide?

4. How does temperature affect the rate of reaction? At what temperature do you think that the enzyme catalase is most effective?

Part E: What Is the Effect of pH on Catalase Activity?

Steps:

1. Add 2 mL of H₂O₂ to each of 5 clean test tubes. Measure the pH of the liquids.

Tube 1—add 2 mL  of acetic acid  pH = _____

Tube 3—add 2 mL  of baking soda (base)  pH = _____

Tube 5—add 2 mL drops of water (neutral)   pH = _____

2. Now add liver to each of the test tubes (try to do it all at about the same time, so you can easily compare).

Rate of Reaction for : Acid _____   Neutral _______     Base _______

Questions:

1. Write data from your steps.

2. How does pH affect the rate of reaction? At what pH do you think that the enzyme catalase is most effective?

Part F: Design your own experiment

       Some people are lactose intolerant, meaning that they cannot eat dairy products because they are unable to digest the lactose (sugar from milk) in milk products.  People that are lactose intolerant lack the enzyme (lactase) that helps to break down the lactose.  There is a pill available called lactaid that helps to break down this sugar by giving them their missing enzyme, lactase. 

       Benedict’s solution is an indicator that shows the amount of glucose (simple sugar) present in a sample. Like a pH indicator it will change color based on the amount of glucose present. When lactose is broken down by the enzyme, more and more glucose will be present and the sample will change color to show that increase in sugar.

       How could you design an experiment to show how quickly lactaid breaks down lactose? What would be your steps that you would follow in your experiment?

1. Write down your steps to your experiment and be specific to what you would you do and how much materials you would use and need. 

2. What could you experiment with to show different experimental conditions to show in what conditions the lactaid is most effective? (Hint: think about the different trials you do with the hydrogen per