What Are Enzymes

Enzymes in the Body Enzymes are molecules in the human body that help speed up chemical reactions. Some enzymes help with the digestion of food in the body, but there are thousands of different kinds of enzymes, each designed to help with a specific reaction. For example, while you might use hydrogen peroxide externally, when hydrogen peroxide forms inside the body, it is harmful to cells. Luckily, there is an enzyme that helps neutralize oxidative compounds like hydrogen peroxide. The enzyme catalase helps protect the body from oxidative cell damage by breaking down hydrogen peroxide to water and oxygen. An enzyme has an active site to which specific compounds attach. The molecules in the compound are referred to as substrates. Once the substrates attach to the enzyme, the chemical reaction is sped up, the reaction takes place, and the reaction products are released. In the case of hydrogen peroxide, water and oxygen are released. Once the reaction is complete, the enzyme is available again for another substrate, and the process repeats. Students can see how this process works with a hands-on science activity that simulates the function of catalase enzymes in the body. Using hydrogen peroxide and yeast (which contains catalase), students are guided in a hands-on experiment with a control and sample solutions containing varying amounts of hydrogen peroxide. When hydrogen peroxide breaks down into oxygen and water, you can see the release of oxygen in the formation of bubbles (or foam). Observing and comparing the visible changes that occur with each sample solution, students can better visualize the enzyme activity that happens in the body. The Exploring Enzymes activity contains the directions for this family-friendly science activity.

Making Connections Students interested in the function of enzymes, may also enjoy science projects and activities like these:      

A Juicy Project: Extracting Apple Juice with Pectinase Enzyme-Catalyzed Reactions-- What Affects Their Rates? I Love Ice Cream, But It Doesn't Love Me: Understanding Lactose Intolerance Liver Stinks! The Liver: Helping Enzymes Help You! Which Fruits Can Ruin Your Gelatin Dessert?

(https://www.sciencebuddies.org/blog/enzymes-foam-and-hydrogen-peroxide)

Enzymes: The Little Molecules That Bake Bread By Emily Buehler on September 28, 2012

When I first began making bread, the science involved was always in the back of my mind. I had an idea of what occurred—my diagram for the chemical reactions in dough looked something like this:

When I started preparing a manual for a bread-making class, however, I really began to wonder about the details. Is the sugar for fermentation part of flour? How exactly does the yeast process this sugar? Do all the complex flavors of bread really come from one organic molecule, ethanol? Numerous trips to the university libraries helped me understand the enzymes involved in making the dough. When I realized that flour contains a very small amount of sugar, only one to two percent, I thought, “Wait a minute, how is that possible? That’s not enough to make dough rise.” Then I figured out that the starch in flour provides most of the sugar for fermentation, and the starch must be broken down into sugar before it can be fermented. This breakdown is the work of enzymes. An enzyme is defined as a large molecule, usually a protein, that catalyzes a biological reaction. This means that the enzyme speeds up the reaction by reducing whatever energy barrier is preventing the reaction from happening quickly and easily. When two molecules bump into each other, there is a chance they will react to form new molecules. Sometimes this happens easily—the two molecules each have an unstable site, for example, and when they bump, a bond forms between the sites, creating a new, stable molecule. In other cases, however, bonds in the reacting molecules must break (which requires energy) before new bonds can form. The amount of energy needed to break the old bonds is the energy barrier to the reaction. This is represented by the solid line in the diagram below. One way to increase the speed of a reaction is to heat it up. Hotter molecules move faster; they possess more energy. When two of them collide, there is a greater chance that the necessary bonds will break and reaction will occur. If more molecules possess the energy needed to get over the barrier, more of the reaction occurs. The other way to speed up a reaction is to reduce the barrier, as shown by the dashed line in the diagram. When less energy is needed for the reaction, more molecules will possess enough energy to get over the barrier. Reducing the barrier is the job of catalysts. They alter the situation to reduce the barrier to reaction. Enzymes are a subset of catalysts; they work on biological reactions. About 4000 reactions are known to involve enzymes, including most of the

reactions that occur in the human body and several reactions in bread dough, described next.

Enzymes catalyze three main reactions in bread-making: breaking starch into maltose, a complex sugar; breaking complex sugars into simple sugars; and breaking protein chains. The breakages could happen without enzymes, but the energy barrier is so large that it is very unlikely. Essentially, the enzymes are necessary for the reactions to occur. It is easy to start seeing enzymes as little critters that come in, recognize the site where they can work, and begin to chew on bonds or snap them in half. While this is a convenient picture, it does a disservice to the marvels of biology. Enzymes do not think or act, but still manage to arrive at the sites where they are needed. Each enzyme has a very specific job to do and only interacts with the appropriate molecules for which it is designed, ignoring all others. Enzymes work efficiently and are not used up by the process; after the reaction occurs, the original enzyme molecule is left intact and can proceed to a new site. If the enzyme does not think, how does it manage to perform its specific task? The simplified picture presented in general chemistry textbooks is called the “lock and key model.” An enzyme has a specific shape that fits together with the substrate, the molecule on which it will be working. The enzyme bonds to the substrate with a weaker chemical bond, a hydrogen bond or hydrophobic bond, for example. It alters the substrate in a way that makes reaction favorable. Once reaction occurs, the enzyme releases the products and moves on. For example, the substrate sucrose is a complex sugar that can react with a water molecule to form two simple sugar molecules, glucose and fructose.

There is an energy barrier to the reaction because it takes a lot of energy to break the middle bond of the sucrose. The enzyme sucrase fits together with the sucrose (below). In order to bond to the enzyme, the sucrose must stretch. This stretching weakens the sucrose’s middle bond, which becomes susceptible to attack by water molecules. The energy barrier has been lowered. When a water molecule comes along, the middle bond easily breaks and reacts with the water molecule. The enzyme is now holding the product molecules, which it releases. Sucrose has been broken into glucose and fructose. Another example emphasizes the bonding nature of the enzymes; they are not simply fitting into substrates like puzzle pieces, snapping into place. Bonds must form. Once bonded, the active site of the enzyme is positioned near the reaction site of the substrate, which it alters to reduce the energy barrier. In this example, the substrate is a protein. Proteins are chains of amino acids linked by peptide bonds. When a peptide bond forms, a water molecule is released.

A water molecule can come back and break a peptide bond, but it usually does not have enough energy. The enzyme carboxypeptidase catalyzes the breaking of the last peptide bond in the protein chain, releasing the end amino acid. Carboxypeptidase contains a zinc atom with a positive charge. This zinc atom bonds with the protein near the last peptide bond, pulling the electrons of the bond away from it and, thus, weakening it (below). The enzyme also has a pocket area composed of hydrophobic atoms; if the terminal amino acid has a hydrophobic group on it, the group is attracted to this pocket and held by it. In addition, carboxypeptidase can form hydrogen bonds with the terminal amino acid, further securing it in place.

When a water molecule encounters the weakened peptide bond, it likely now has enough energy to break it, recombining with the broken ends to reform the loose amino acid. The various bonds holding the enzyme to the protein substrate are weakened, and the enzyme is released. The first enzyme to take action in bread dough is amylase. Amylase acts on starch (either amylose or amylopectin), breaking the starch chain between adjacent sugar rings. There are two kinds of amylase: α-amylase (alphaamylase) randomly breaks the chain into smaller pieces while β-amylase (beta-amylase) breaks maltose units off the end of the chain. Amylase is found in flour. Wheat kernels contain amylase because they need to break starch down into sugar to use for energy when the kernels germinate. The amount of amylase varies with the weather and harvesting conditions of the wheat, so mills generally test for it and add extra or blend flours to get an appropriate amount. Amylases are mobilized when water is added to the flour. This is one reason why doughs with a higher hydration often ferment faster—the amylases (and other enzymes) can move about more effectively. To reach the starch molecules, amylases must penetrate the starch’s granules; thus, most of the action in bread dough happens at broken granules, where the starch is available for reaction. Fortunately, a percentage of starch granules are damaged during milling and accessible by the amylases. An amylase is a big molecule, with hundreds of amino acids linked together. Many different groups contribute to the bonding between the amylase and the starch substrate. In addition, there are several different amylase molecules, and each functions differently. The examples of enzyme action presented above give the general idea. Because of amylase, some of the starch in bread dough is broken into maltose, a double-ring sugar composed of two glucose molecules; but fermentation reactions require single glucose rings. Simple sugars like glucose also provide flavor to the bread and participate in browning reactions that occur at the crust during baking. Fortunately, the yeast used in bread-making contains the enzyme maltase, which breaks maltose into glucose. When the yeast cell encounters a maltose molecule, it absorbs it. Maltase then bonds to the maltose and breaks it in two. Yeast cells also contain invertase, another enzyme that can break sucrose, like the sucrase described above. This enzyme works on the small percentage of

sucrose found in the flour. These two enzymes are responsible for producing much of the glucose needed by the yeast for fermentation. The other major enzyme at work in bread dough is protease. Protease acts on protein chains, breaking the peptide bonds between amino acids. Carboxypeptidase, described above, is an example of a protease. There are hundreds of proteases, but only a few are found in bread dough, where they chop the gluten into pieces. Proteases occur naturally in flour, yeast cells, and malt. Their levels are measured at the mill and adjusted in the same way that amylase levels are adjusted. Proteases in bread dough have been the subject of scientific research for the past hundred years. There has been much debate about their importance. In the early years, scientists were trying to prove their existence and measure relative activity in different brands of flour. They amplified the protease activity by adding non-gluten substrates to the mix. These substrates were ones that protease readily attacks. Eventually someone thought to look at protease activity in normal bread dough and found very little activity. It seems, however, that this very small activity might be just what is needed in bread dough. Too much protease activity would break up the gluten, destroying the network that forms during kneading. A little bit, however, softens the dough and makes it more workable. If the dough is allowed to autolyse (i.e., rest) or if preferments are used, proteases have time to work before kneading, making the dough easier to knead. (I wonder if this is the origin of the word “autolyse,” from “autolysis,” which means “self-breaking” and could refer to the protein proteases at work on the protein chains.) In addition to affecting the dough’s consistency, proteases affect its flavor. Proteases result in single amino acids when they break the last peptide bond of the protein chain. These amino acids can participate in the flavor and browning reactions that occur at the crust during baking. So now, my simplified diagram of the chemical reactions in bread dough looks more like this: This diagram includes the presence of enzymes. Without enzymes, breadmaking would not be possible. Then again, neither would we.

Introduction Have 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 damage. Background Enzymes are essential for our survival. These proteins, made by our cells, help transform chemicals in our body, 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 (the chemicals doing the reacting). Each enzyme has an active site, which is where the reaction takes place. 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. 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, which can occur when cells or other molecules in the body come into contact with oxidative compounds. This damage is a natural result of reactions happening inside your cells. The reactions can include byproducts such as hydrogen peroxide, which can be harmful to the body, just as how a by-product of a nice bonfire can be unwanted smoke that makes you cough or stings your eyes. To prevent such damage, the catalase enzyme helps getting rid of these compounds by breaking up hydrogen peroxide (H2O2) into harmless water and oxygen. Do you want to see the catalyze enzyme in action? In this activity you will disarm hydrogen peroxide with the help of catalase from yeast. Materials

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Safety goggles or protective glasses

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Five teaspoons of dish soap

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One package of dry yeast

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Hydrogen peroxide, 3 percent (at least 100 mL)

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Three tablespoons

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One teaspoon

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Five 16-ounce disposable plastic cups

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Tap water

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Measuring cup

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Permanent marker

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Paper towel

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Workspace that can get wet (and won't be damaged by any spilled hydrogen peroxide or food-colored water)

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Food coloring (optional) Preparation Take one cup and dissolve the dry yeast in about one-half cup of warm tap water. The water shouldn't be too hot but close to body temperature (37 Celsius). Let the dissolved yeast rest for at least five minutes.

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Use the permanent marker to label the remaining four cups from one to four.

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To all the labeled cups, add one teaspoon of dish soap.

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To cup one no further additions are made at this point.

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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 it on your skin, make sure to rinse the affected area with plenty of water.

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To cup two, add one tablespoon of 3 percent hydrogen peroxide solution. Use a fresh spoon for the hydrogen peroxide.

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To cup three, add two tablespoons of the hydrogen peroxide.

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To cup four, add three tablespoons of the hydrogen peroxide.

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Optionally, you can add a drop of food color to each of the labeled cups. (You can choose a different color for each one for easy identification) Procedure

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Take cup number one and place it in front of you on the work area. With a fresh tablespoon, add one 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 two 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 three. Do you see the same reaction taking place? Is the result different or the same compared to cup number two? Finally, add one tablespoon of yeast solution to cup number four. Do you see more or less reaction products compared to your previous results? Can you explain the difference? Place all four 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 one and add one additional tablespoon of 3 percent 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? Extra: Repeat this activity, 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? Extra: So far you have observed 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 three tablespoons of hydrogen peroxide, starting with one teaspoon. Do you observe any differences, or does the concentration of catalase not matter in your reaction? Extra: 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 (an acid) or baking soda (a base), 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? Extra: Can you find other sources of catalase enzyme that you could use in this activity? Research what other organisms, plants or cells contain catalase and try using these for your reaction. Do they work as well as yeast? Observations and results You probably saw lots of bubbles and foam in this activity. What made the foam appear? When the enzyme catalase comes into 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 one you shouldn't 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 one, which should have resulted in a similar amount of foam as in cup two. 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 doing the extra steps in the procedure. Cleanup Pour all the solutions into the sink and clean all the spoons with warm water and dish soap. Wipe your work area with a wet paper towel and wash your hands with water and soap. (https://www.scientificamerican.com/article/exploring-enzymes/) Hydrogen Peroxide Breakdown in Liver vs. Potato What gas was produced by the breakdown of hydrogen peroxide? Oxygen gas was produced Describe the test that was performed in order to identify the gas.

A glowing splint of a match was lit, blown out then inserted into the test tube. The match relighting in the test tube indicates oxygen gas is present. Can hydrogen peroxide be broken down by catalyst other than those found in a living system? Hydrogen peroxide can be broken down by manganese dioxide because it has catalytic properties. It is unstable which makes it very reactive. It even breaks down in the presence of light. It increases the rate of reaction without being changed. Sand however is not able to break it down because it contains no catalytic properties. Explain how temperature affected the enzyme’s function Increasing the temperature increased the rate of reaction. There is a higher energy when heated. The enzyme was able to catalyze the reaction more quickly. This is only until the point until denaturation. At 40 degrees, the enzyme would experience denaturation causing the rate of reaction to drop. The enzyme would be damaged and not be able to perform the same way. How did particle size affect the rate of reaction? Smaller size of particles increased the rate of reaction because smaller particles consume less energy than larger ones to break down molecules, therefore the reaction would happen faster. Larger particles decreased the rate of reaction because they require more energy to break down. Explain why there is a difference in the rates of reaction between the liver and the potato Liver contains more of the enzyme catalase, which breaks down hydrogen peroxide. Liver contains more because it detoxifies substances in the body. A larger amount of catalase lowers the activation energy, therefore speeds up the rate of reaction. The potato contains less of the enzyme catalase, therefore requires more activation energy, slowing down the rate of reaction. Show the fully labeled balanced chemical equation for the decomposition of hydrogen peroxide 2 H2O (aq) –(catalase)—> 2 H2O (l) + O2 (g) hydrogen peroxide enzyme water oxygen gas Why is it possible to use dead cells to study the function of this enzyme? Although the cells are dead, catalase still remains active. It remains active in certain temperatures up until the point of denaturation which occurs above 40 degrees. The organism which contained the cells is gone but the cells are still present and active in certain conditions.

(https://schoolworkhelper.net/hydrogen-peroxide-breakdownliver-vs-potato/) Introduction Your liver is important for cleaning up any potentially dangerous substances you consume. But how does it do it?—With a little help from some complex chemistry. Within your liver, as within every tissue in the body, many chemical reactions occur. Often these reactions require "help" to happen at a faster speed, and this can be supplied by enzymes—tiny types of proteins.

The liver uses specialized enzymes to help it break down toxic substances and make them safer for the body to process. But an enzyme, just like the chemical reactions it modifies, needs certain conditions to do its work. So, some environments can make a liver enzyme effective, whereas others can prevent it from working at all. Background A chemical reaction occurs when compounds come together and their molecules interact to form new compounds. Sometimes these reactions happen by themselves, are usually very fast and spontaneous, and give off energy. Other chemical reactions need energy, without which they would proceed very slowly or not at all. Enzymes can help speed up these types of chemical reactions. Enzymes are large proteins that speed up the rate of a chemical reaction by acting as a catalyst. A catalyst provides the necessary environment for the reaction to occur, thereby quickening it. Certain catalysts work for certain kinds of reactions; in other words, each enzyme has a particular type of reaction that it can activate. Enzymes can be very fussy and sometimes need to be in certain environments or conditions to work well—or at all. Some enzymes can even be damaged, such as when exposed to too much heat. A damaged enzyme may no longer work to catalyze a chemical reaction. Catalase is an enzyme in the liver that breaks down harmful hydrogen peroxide into oxygen and water. When this reaction occurs, oxygen gas bubbles escape and create foam. Materials • Raw liver (fresh or frozen, thawed; one quarter pound) • Knife • Cutting board • Blender • Water • Refrigerator • Medicine dropper • Large plate • Hydrogen peroxide (new or recently purchased bottle works best) • Measuring teaspoon • Two bowls • Vinegar • Baking soda • Microwave-safe bowl (with a cover) • Microwave oven

Preparation • Completely disinfect any surface that the raw liver touches during this activity. • On the cutting board, carefully cut the liver into little, cube-shaped pieces, about one to two centimeters long. Be careful using the sharp knife. (An adult may need to help with this.) • Place the liver cubes into a blender and add an equal volume of water. Blend on high speed, pulsing when necessary, until the liver is smooth and no chunks are present. Be careful of the sharp blades in the blender. • Keep the blended liver in the refrigerator. Procedure • Put one drop of the blended liver on the large plate. To the blended liver drop, add one drop of hydrogen peroxide. You should see a lot of bubbles! What do you think the bubbles are made of? This shows that the liver enzyme catalase is working to start the chemical reaction that breaks down the hydrogen peroxide that would be harmful to the body into less dangerous compounds. • To test the effect of an acid on the liver enzyme, put one teaspoon of the blended liver in a bowl and mix it well with one teaspoon vinegar. What is the color and consistency of this mixture? Put one drop of the mixture on a clean part of the large plate and add one drop of hydrogen peroxide to it. Compared with the untreated blended liver, did more, less or about the same amount of bubbles form? Did they form more slowly, more quickly or at about the same rate? • To test the effect of a base, put one teaspoon of the blended liver in a bowl and mix it with one teaspoon baking soda. What is the color and consistency of this mixture? Put one drop of the mixture on a clean part of the large plate and add one drop of hydrogen peroxide to it. Did more, less or about the same amount of bubbles form? Did they form more slowly, more quickly or at about the same rate? • To test the effect of heat, put one teaspoon of the blended liver into a microwave-safe bowl. Cover the bowl and microwave it on high for 20 seconds. How does the blended liver look after heating? Remove a drop-size amount of the heated liver and put it on a clean part of the large plate. Add one drop of hydrogen peroxide to it. Did more, less or about the same amount of bubbles form? Did they form more slowly, more quickly or at about the same rate? • Based on your observations, under which condition(s) does it look like the enzyme works best? Which condition(s) makes it work the worst? Why do you think this is so?

• Extra: Try experimenting with other conditions. For example, try freezing some blended liver or mixing it with salt and then test the enzyme's activity. Or you could try adding more than one teaspoon of vinegar or baking soda and then test the enzyme. Under which conditions does the enzyme work well, and under which ones does it work poorly? • Extra: You could try this activity again using another enzyme, called bromelain, which digests proteins and can be extracted from pineapples. One protein that is fun to digest using bromelain is gelatin, which is found in many puddings and gelatinous desserts. How do different conditions affect the ability of bromelain to digest proteins? Observations and results When exposed to hydrogen peroxide, did the blended liver bubble less when mixed with either the vinegar or baking soda compared with when it was untreated? Did it bubble even less after it was microwaved? An enzyme needs certain conditions to work, and the ideal environment can be a hint as to where the enzyme normally works in the body. And because different body tissues have distinct environments—acidic or warm—each enzyme is tuned to work best under specific conditions. Different tissues in the body have different pHs (pH is a measure of how basic or acidic a solution is). The liver maintains a neutral pH (about pH 7), which is easiest for its enzymes, such as catalase, to work in. Consequently, when exposed to hydrogen peroxide the liver should have produced more bubbles (oxygen gas), and at a faster rate, when it was untreated than when exposed to vinegar or baking soda. (It may have bubbled more when treated with baking soda, compared with vinegar, because it might have been better able to return the pH to around 7.) Similarly, enzymes in the liver are also used to functioning at body temperature (37 degrees Celsius), so microwaving the blended liver to a temperature hotter than that should have damaged the catalase enzyme and clearly decreased the amount of bubbles when it was exposed to hydrogen peroxide. Cleanup Safely dispose of any raw liver meat used in this activity by putting it in the trash when you are done. Completely disinfect any surfaces that the raw liver

meat touched during this activity, and be sure to thoroughly wash your hands with soap and warm water. (https://www.scientificamerican.com/article/bring-science-home-liver-helping-enzymes/)

How do living cells interact with the environment around them? All living things possess catalysts, or substances within them that speed up chemical reactions and processes. Enzymes are molecules that enable the chemical reactions that occur in all living things on earth. In this catalase and hydrogen peroxide experiment, we will discover how enzymes act as catalysts by causing chemical reactions to occur more quickly within living things. Using a potato and hydrogen peroxide, we can observe how enzymes like catalase work to perform decomposition, or the breaking down, of other substances. Catalase works to speed up the decomposition of hydrogen peroxide into oxygen and water. We will also test how this process is affected by changes in the temperature of the potato. Is the process faster or slower when compared to the control experiment conducted at room temperature? Problem What happens when a potato is combined with hydrogen peroxide? Materials   

1 Potato Hydrogen peroxide Small glass beaker or cup Procedure

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Divide the potato into three roughly equal sections. Keep one section raw and at room temperature. Place another section in the freezer for at least 30 minutes. Boil the last section for at least 5 minutes. Chop and mash a small sample (about a tablespoon) of the room temperature potato and place into beaker or cup. 6. Pour enough hydrogen peroxide into the cup so that potato is submerged and observe. 7. Repeat steps 5 & 6 with the boiled and frozen potato sections. Observations & Results Watch each of the potato/hydrogen peroxide mixtures and record what happens. The bubbling reaction you see is the metabolic process of decomposition, described earlier. This reaction is caused by catalase, an enzyme within the potato. You are observing catalase breaking hydrogen peroxide into oxygen and water. Which potato sample decomposed the most hydrogen peroxide? Which one reacted the least?

Why? You should have noticed that the boiled potato produced little to no bubbles. This is because the heat degraded the catalase enzyme, making it incapable of processing the hydrogen peroxide. The frozen potato should have produced fewer bubbles than the room temperature sample because the cold temperature slowed the catalase enzyme’s ability to decompose the hydrogen peroxide. The room temperature potato produced the most bubbles because catalase works best at a room temperature. Conclusions Catalase acts as the catalyzing enzyme in the decomposition of hydrogen peroxide. Nearly all living things possess catalase, including us! This enzyme, like many others, aids in the decomposition of one substance into another. Catalase decomposes, or breaks down, hydrogen peroxide into water and oxygen. Want to take a closer look? Go further in this experiment by looking at a very small sample of potato combined with hydrogen peroxide under a microscope! Author: Justine Rembac (https://www.education.com/science-fair/article/activator/)

What are enzymes? (http://brilliantbiologystudent.weebly.com/enzymes.html) Structure of Chymotrypsin, a protease enzyme which is active in the duodenum. Enzymes are biological catalysts. A catalyst is a substance which speeds the rate of reaction but remains unchanged in the reaction. Catalysts reduce the activation energy needed for a reaction. Enzymes are proteins and occur naturally in living biological systems, acting in many metabolic pathways. The activity of enzymes are affected by pH, temperature, enzyme concentration and substrate concentration. Enzymes have optimum pH and optimum temperatures, at which they experience maximal activity. Enzymes are highly specific, acting upon a single substrate or group of related substrates. Enzymes have an active site - a small portion of the molecule which is complementary in shape to a portion of the substrate. The substrate binds to the active site of the enzyme forming the enzyme-substrate complex. Strain is induced in the bonds causes them to cleave and the the products leave the active site, leaving it available for further reactions. The reaction of enzymes are reversible. Learning Objectives

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Explain the properties and functions of enzymes Explain how various factors - pH, temperature, substrate concentration, enzyme concentration - can affect the rate of enzyme-catalyzed activity Explain the action of inhibitors - competitive or non-competitive, reversible or irreversible.

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Enzyme Experiments 

To investigate the effect of substrate concentration on enzyme activity To investigate the effect of enzyme concentration on enzyme activity To investigate the effect of temperature on enzyme activity To investigate the effect of pH on enzyme activity

To investigate the effect of substrate concentration on enzyme activity 

To investigate the effect of different pH values on enzyme activity

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To investigate the effect of temperature on enzyme activity

Enzyme and substrate pairs commonly used in the for biology experiments are:   

Catalase (from raw potato tuber) & hydrogen peroxide Amylase (commercial preparation) & starch Sucrase - invertase is the most common sucrase ( commercial preparation) & sucrose.

Factors affecting Enzyme activity (http://www.nuffieldfoundation.org/practical-biology/factors-affecting-enzyme-activity) Enzymes are sophisticated catalysts for biological processes. These practicals (and the practicals at intermediate level) give you opportunities to explore how enzyme activity changes in different conditions. Enzyme experiments often provide real ‘messy’ data, because their activity can change dramatically from one lesson to the next. 

Microscale investigations of catalase activity in plant extracts Adsorb microscale quantities of plant extract onto filter paper discs and assess catalase activity by comparing times taken for the discs to surface in hydrogen peroxide solution.

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Investigating an enzyme-controlled reaction: catalase and hydrogen peroxide concentration Use catalase in pureed potato and investigate the effect of changing hydrogen peroxide concentration on rate of production of oxygen.

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Investigating effect of temperature on the activity of lipase A simple protocol that measures the effect of changing temperature on the time taken for lipase to break down the fat in milk to form fatty acids (and glycerol).

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Investigating the effect of pH on amylase activity Measure the time taken for amylase to completely break down a sample of starch, using buffers for different pHs.

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Investigating effect of concentration on the activity of trypsin Measure the time taken for different concentrations of trypsin to digest the gelatine coating on exposed photographic film and release the blackened silver halides.