The Liver Enzyme Lab

THE LIVER ENZYME

Introduction to LAB Enzymes In each individual cell of a human there are many chemical reactions taking place, performing the necessary functions for being a large, complex, multicellular organism. This is relatively easy to understand. How do these reactions occur? This is not so easy to understand. Chemical reactions involve the breaking and reforming of chemical bonds between molecules (substrate(s) of the reaction), which are transformed into different molecules (product(s) of the reaction). Chemical reactions can occur spontaneously (without added energy or intervention), and indeed many of the chemical reactions necessary for life processes are spontaneous; some however, are not. Metabolic pathways are processes, which involve many chemical reactions that occur in a specific order.

For example, to get energy out of a molecule of glucose, a series of reactions must take place in a specific order to break the bonds between the carbons of the glucose molecule. In addition, you have to rely on a series of chemical reactions that break down stored glycogen into glucose molecules to have glucose molecules in the first place. If you had to rely on these reactions to take place spontaneously, you would wait a very long time -- you wouldn't be here! Enzymes catalyze chemical reactions so that they occur in a timely and sequential manner to produce a product.

Enzymes are biological catalysts. They help to increase the rate of chemical reactions. Enzymes are most often proteins and their three-dimensional shape is important to their catalytic activity. Because of their 3-D shape, enzymes are highly specific for the reactions that they catalyze. In other words, they are highly specific for the substrates that they will act upon. So any one "function", such as getting energy from a glucose molecule, actually involves many reactions, each with a specific enzyme.

Enzyme activity is influenced by many factors. You will conduct a series of experiments and observe the reaction that takes place in several test tubes. The reaction that we will be studying is the decomposition of 6% hydrogen peroxide into water and oxygen gas. This reaction will be catalyzed by the catalase enzyme found in liver. Catalase is an enzyme, which is found in many cells, but in highest levels in the liver because the liver often functions to break down toxins present in the blood.

PRELAB: 1. What is an enzyme? 5. Complete the following sentence: a. All enzymes are ______, but not all 2. What is the function of an enzyme? ______are enzymes. 3. Define catalyst. 4.

6. THREE (3) factors that will effect the effectiveness of enzymes: a. b. c.

7. Highlight the reactant(s) in the equation above yellow. Highlight the product(s) in the equation above green.

8. What is our substrate in this lab? 9. What is our enzyme in this lab?

10.What indication will we have that the enzyme is working? HINT: Look at the products, what would having these together LOOK like?

MATERIALS:  5 test tubes  1 test tube rack

 Hydrogen peroxide (H2O2)

 Distilled water (d H2O)  Raw liver  Boiling water bath (hot plate, water, beaker)  Ice Bath (ice, water, cooler)

PROCEDURE: 1. You will prepare the contents as outlined below for each corresponding test tube: a. Test tube #1 – Water b. Test tube #2 – Water & Liver c. Test tube #3 – Water, Liver, & *H2O2 d. Test tube #4 – Water, Liver (that has been boiled several minutes) & *H2O2 e. Test tube #5 – Water, Liver (that has been cooled on ice for several minutes) & *H2O2

* VERY IMPORTANT: DO NOT ADD THE H2O2 to tubes #3-5 until you are running the experiment for that test tube. 2. Your data table should have the following format: TEST TUBE CONTENTS HYPOTHESIS OBSERVATIO INTERPRETATIONS # (What do you think will N (Why did this happens?) happen?) (What really happened?)

3. Record a hypothesis for EACH test tube set-up BEFORE beginning the lab. 4. The volume of water will always be approximately 5mL 5. The size of the piece of liver should be approximately the same and relatively small. 6. Place test tubes 4 & 5 in ice/water bath as soon as you prepare them. 7. Test ONE test tube at a time. a. Set-up your test tube b. Add approximately 5mL of H2O2 (if indicated) c. Record your observations for ~3 – 5 minutes. d. Interpret what you think has happened to the enzyme. 8. CLEAN UP; CLEAN UP; EVERYBODY, EVERYWHERE!!!! CLEAN UP, CLEAN UP, EVERYBODY DO YOUR SHARE!!!

ANALYSIS: 1. What effect did the water have on enzyme function? a. How do you know? 2. What effect did the ice have on enzyme function? a. How do you know? 3. What effect did the heat have on enzyme function? a. How do you know? b. Explain why you think this happened? 4. Why did you include test tube 1 in the experiment? 5. Why is it important to maintain the same volume of water and H2O2? 6. What is the independent variable? 7. What is the dependent variable? 8. Explain how enzyme function is like a lock and key. (You may draw and label a diagram in addition to writing an explanation if that makes it easier for you.) 9. The function of the liver is to break down fats and build certain proteins. Cirrhosis of the liver is a disease which causes the liver to become thickened and “rubbery.” Hypothesize how enzyme function in the liver would be affected in a person with cirrhosis. Be sure to include references and citations in your explanation.