IntroductionHave you ever wondered how all the food that you eat gets digested? It is not only the acid in your stomach that breaks down your food—many little molecules in your body, called enzymes, help with that too. Enzymes are special types of proteins that speed up chemical reactions, such as the digestion of food in your stomach. In fact, there are thousands of different enzymes in your body that work around-the-clock to keep you healthy and active. In this science activity you will investigate one of these enzymes, called catalase, to find out how it helps to protect your body from cell damage.
- Safety goggles or protective glasses
- Dish soap (5 teaspoons)
- Dry yeast, 1 package (7 grams)
- Hydrogen Peroxide, 3% (at least 100 mL)
- Tablespoons (3)
- Teaspoon (1)
- Plastic Cups, 16 oz (5)
- Tap water
- Measuring cup
- Permanent marker
- Paper towel
- Optional: Food coloring
- Take one cup and dissolve the dry yeast in about ½ cup of warm tap water. The water should not be too hot but close to body temperature (37°C). Let the dissolved yeast rest for at least 5 minutes.
- Use the permanent marker to label the remaining 4 cups from 1 to 4.
- To all the labeled cups, add 1 teaspoon of dish soap.
- To cup 1 no further additions are made at this point.
- Before using the hydrogen peroxide, put on your safety goggles to protect your eyes. In case you spill hydrogen peroxide, clean it up with a wet paper towel. If you get H₂O₂ on your skin, make sure to rinse the affected area with plenty of water.
- To cup 2, add ½ tablespoon of 3% hydrogen peroxide solution. Use a fresh spoon for the H₂O₂.
- To cup 3, add 1 tablespoon of 3% hydrogen peroxide.
- To cup 4, add 2 tablespoons of 3% hydrogen peroxide.
- Optional: To each of the labeled cups add a drop of food color. You can choose a different color for each one.
- Choose a work area that can tolerate spills of the prepared solutions.
- Take cup number 1 and place it in front of you on the work area. With a fresh tablespoon, add 1 tablespoon of the dissolved yeast solution to the cup and swirl it slightly.What happens after you add the yeast? Do you see a reaction happening?
- Place cup number 2 in front of you and again add one tablespoon of yeast solution to the cup.Once you add the enzyme, does the catalase react with the hydrogen peroxide? Can you see the reaction products being formed?
- Add one tablespoon of yeast solution to cup number 3.Do you see the same reaction taking place? Is the result different or the same compared to cup number 2?
- Finally, add one tablespoon of yeast solution to cup number 4.Do you see more or less reaction products compared to your previous results? Can you explain the difference?
- Place all 4 cups next to each other in front of you and observe your results.Did the enzymatic reaction take place in all of the cups or was there an exception? How do the results in each cup look different? Why do you think this is the case?
- Now, take cup number 1 and add one additional tablespoon of 3% hydrogen peroxide to the cup. Swirl the cup slightly to mix the solution.What happens now? Looking at all your results, what do you think is the limiting factor for the catalase reaction in your cups?
You probably saw lots of bubbles and foam in this activity. What made the foam appear? The answer is, when the enzyme catalase comes in contact with its substrate, hydrogen peroxide, it starts breaking it down into water and oxygen. Oxygen is a gas and therefore wants to escape the liquid. However, the dish soap that you added to all your solutions is able to trap the gas bubbles, which results in the formation of a stable foam. As long as there is enzyme and hydrogen peroxide present in the solution, the reaction continues, and foam is produced. Once one of both compounds is depleted, the product formation stops. If you do not add dish soap to the reaction, you will see bubbles generated but no stable foam formation.
If there is no hydrogen peroxide present, the catalase cannot function, which is why in cup 1 you should not have seen any bubble or foam production. Only when hydrogen peroxide is available, the catalase reaction can take place as you probably observed in the other cups. In fact, the catalase reaction is dependent on the substrate concentration. If you have an excess of enzyme but not enough substrate, the reaction will be limited by the substrate availability. Once you add more hydrogen peroxide to the solution, the reaction rate will increase as more substrate molecules can collide with the enzyme, forming more product. The result is an increasing amount of foam produced in your cup as you increase the amount of H₂O₂ in your reaction. You should have seen more foam being produced once you added another tablespoon of hydrogen peroxide to cup 1, which should have resulted in a similar amount of foam as in cup 3. However, at some point you will reach a substrate concentration at which the enzyme gets saturated and becomes the limiting factor. In this case you have to add more enzyme to speed up the reaction again.
Many other factors affect the activity of enzymes as well. Most enzymes only function under optimal environmental conditions. If the pH or temperature deviates from these conditions too much, the enzyme reaction slows down significantly or does not work at all. You might have noticed that when you continued with the further exploration.
Enzymes are essential for life. They are proteins made by our cells to help transform chemicals in our body. Enzymes play a vital role in the chemical reactions that take place in our body, by functioning as a catalyst. A catalyst gets reactions started and makes them happen faster by increasing the rate of a reaction that otherwise might not happen at all, or would take too long to sustain life. However, a catalyst does not take part in the reaction itself—so how does this work? Each chemical reaction needs a minimum amount of energy to make it happen. This energy is called the activation energy. The lower the activation energy of a reaction, the faster it takes place. If the activation energy is too high, the reaction does not occur.
Enzymes have the ability to lower the activation energy of a chemical reaction by interacting with its reactants. Each enzyme has an active site, which is where the reaction takes place (Figure 1). These sites are like special pockets that are able to bind a chemical molecule. The compounds or molecules the enzyme reacts with are called their substrates. The enzyme pocket has a special shape so that only one specific substrate is able to bind to it, just like only one key fits into a specific lock. Once the molecule is bound to the enzyme, the chemical reaction takes place. Then, the reaction products are released from the pocket and the enzyme is ready to start all over again with another substrate molecule.
The enzyme binds its substrate at the active site to form an enzyme/substrate complex. Once the reaction is completed, the reaction products are released from the active site of the enzyme.
Figure 1. Schematic drawing of an enzyme reacting with its substrate.
Catalase is a very common enzyme that is present in almost all organisms that are exposed to oxygen. The purpose of catalase in living cells is to protect them from oxidative damage. Oxidative damage is damage to cells or other molecules in the body caused by oxidative compounds. This damage is a natural result of reactions happening inside your cells, that result in by-products such as hydrogen peroxide, that can be harmful to the body, just like how a by-product of a nice bonfire can be unwanted smoke that makes you cough and your eyes sting. To prevent such damage, the catalase enzyme helps getting rid of these compounds by breaking up hydrogen peroxide into harmless water and oxygen (Figure 2).
Figure 2. Decomposition of hydrogen peroxide catalyzed by catalase.
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For Further Exploration
- Repeat this experiment, but this time do not add dish soap to all of the reactions. What is different once you remove the dish soap? Do you still see foam formation?
- So far you have tested the effect of substrate (H₂O₂) concentration on the catalase reaction. What happens if you keep the substrate concentration constant but change the concentration of the enzyme? Try adding different amounts of yeast solution to 3 tablespoons of hydrogen peroxide, starting with 1 teaspoon. Do you observe any differences, or does the concentration of catalase not matter in your reaction?
- What happens if the environmental conditions for the enzyme are changed? Repeat the catalase reaction but this time vary conditions such as the pH by adding vinegar or baking soda, or change the reaction temperature by heating the solution in the microwave. Can you identify which conditions are optimal for the catalase reaction? Are there any conditions that eliminate the catalase activity?
- Can you find other sources of catalase enzyme that you could use in this experiment? Research what other organisms, plants or cells contain catalase and try using these for your reaction. Do they work as well as yeast?
- 5-PS1-4. Conduct an investigation to determine whether the mixing of two or more substances results in new substances.
- HS-PS1-5. Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.
- Ducksters: Biology for Kids: Enzymes
- PDB-101: Catalase
- A Level Notes: Factors affecting Enzyme Activity