Enzyme Teachers Answer Key

Teacher Key Objectives You will use the model pieces in the kit to: • Simulate enzymatic actions. • Explain enzymatic specificity. • Investigate two types of enzyme inhibitors used in regulating enzymatic activity. • Examine how an enzyme may affect activation energy. Introduction Enzymes are specialized proteins that catalyze or speed up chemical reactions within cells. The substance upon which an enzyme acts is called a substrate. Substrates are small molecules. Enzymes: • Accomplish catalysis without being consumed in the reaction. • Catalyzes a specific chemical reaction. The Enzyme in Action Kit © allows you to explore how enzymatic reactions occur. Catabolism Model pieces needed gray A foam piece without stickers green B1 and B2 foam pieces orange C1 and C2 foam pieces 1. The gray foam piece is a model of an enzyme. Place it with the A label facing up. Assemble the two green pieces (B1 and B2) into a single unit to model the substrate in this reaction. 2. Draw and label the enzyme and substrate before the enzymatic action. enzyme substrate Enzyme Action Continues 3. In this first metabolic action, the enzyme will act on the substrate to break it apart. Experiment with the pieces to model how the enzyme and substrate might interact. 4. The substance an enzyme acts upon is referred to as the ___________________________. substrate 5. Place an “X” on the drawing of the enzyme and substrate you created on page 1 to show where the substrate binds to the enzyme. The part of the enzyme that binds the substrate to be acted on is referred to as the active site. Once the substrate is locked into the enzyme, the two green substrate pieces may be easily pulled apart. This type of metabolic process is called catabolism (the breaking down of complex molecules into simpler molecules). 6. Draw and label the enzyme, products and active site after enzymatic action. active site Products enzyme 7. Although the substrate model changed in this reaction, what changes did you observe in the model of the enzyme during this reaction? When the substrate was locked into place on the enzyme, a slight shape change took place in ____________________________________________________________________________________ the enzyme to allow for the substrate to dock. ____________________________________________________________________________________ 8. Why do you think it is an advantage for the enzyme to remain unchanged while catalyzing a chemical reaction? Answers will vary but may include: The enzyme may be used over and over again reducing ____________________________________________________________________________________ the amount of resources the cell would have to use to make more enzyme. The enzyme is ____________________________________________________________________________________ not a direct reactant in the cellular chemical reaction and doesn’t change in order to avoid ____________________________________________________________________________________ interference with cellular reactions. ____________________________________________________________________________________ Enzyme Action Continues Note: A real life example of catabolism occurs when the enzyme sucrase breaks down the substrate sucrose into glucose and fructose (monosaccharides). 9. Given what you now know about catabolism, identify the following components in the model illustrated below: enzyme, substrate, products and active site. products c.____________ b.____________ substrate d.____________ active site enzyme a.____________ Induced Fit Model of Enzyme Action In 1958 scientist Daniel Koshland, Jr., PhD., proposed the induced fit model to describe enzymesubstrate interaction. This model suggests that enzymes are flexible structures in which the binding of the substrate results in small changes to the shape of the active site, maximizing its interaction with the substrate. 10. Describe how the foam catabolism model illustrates the induced fit model of enzymesubstrate interaction. The enzyme shows flexibility as it reshapes slightly to allow for the substrate to dock ____________________________________________________________________________________ into the active site. ____________________________________________________________________________________ 11. Explain the difference between catalysis and catabolism. Catabolism is defined as a metabolic process that breaks down complex molecules into ____________________________________________________________________________________ simpler ones. Catalysis is the increase in the rate of a chemical reaction due to participation of ____________________________________________________________________________________ a substance that can modify the rate of the reaction without being consumed in the process. ____________________________________________________________________________________ Enzyme Action Continues Anabolism Enzymes may also bring substrates together to form a final product. This metabolic process is called anabolism (the building of complex molecules from simpler molecules). 12. Use the gray foam piece and the orange foam pieces (C1 and C2) to simulate an anabolic process. The orange pieces should not be assembled prior to the anabolism action. 13. Sketch and label the enzyme and substrate prior to enzyme action in the space below. enzyme substrate 14. Place the small pointed orange piece (C2) into the enzyme. Join the larger orange piece (C1) to C2. Note that the two pieces lock together to form a final product. 15. In the space below, sketch and label the enzyme and products after the enzyme has acted on the substrate. enzyme product Enzyme Action Continues Note: A real life example of anabolism occurs when RNA polymerase links RNA nucleotides together by catalyzing the formation of a bond between the backbone sugar of one onucleotide to the backbone phosphate of another nucleotide during transcription. 16. Given what you now know about anabolism, identify the substrate in the above diagram. The incoming RNA nucleotides. ____________________________________________________________________________ 17. Explain why the above process is an example of anabolism. Anabolism is the process of bringing substrates together to form a product. The RNA ____________________________________________________________________________ polymerase brings the RNA nucleotides together to form an RNA molecule. ________________________________________________________________________ Lock and Key Model of Enzyme Action In 1894 scientist Emil Fisher wrote, “To use a picture, I would like to say that enzyme and glucoside have to fit to each other like a lock and key in order to exert a chemical effect on each other.” Fisher created a mental model of how an enzyme acts and referred to it as the Lock and Key Model of Enzyme Action. This model suggests that the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another like a key into a lock. 18. Describe how the anabolic process you previously modeled illustrates the lock and key model of enzyme-substrate interaction. The lock and key model suggests that the enzyme does not change shape to accommodate ____________________________________________________________________________________ the substrate. In the anabolic activity, the enzyme model does not change shape when the ____________________________________________________________________________________ substrate is bound. ____________________________________________________________________________________ Enzyme Action Continues Note: Most enzymes catalyze either catabolic OR anabolic processes. There are a few enzymes that do both. ATP synthase and ATPase are the same protein but have different names because they function as enzymes in both catabolic and anabolic reactions. Intermembrane space Diagram A — ATP Synthase Intermembrane space Diagram B — ATPase 19. Describe the action of the enzyme in diagram A. In your description, identify the substrate and enzyme. Diagram A illustrates an anabolic process. The enzyme ATP synthase is putting together ____________________________________________________________________________________ the substrates ADP and Pi to form ATP. Diagram B illustrates a catabolic process where the ____________________________________________________________________________________ enzyme ATP synthase is helping to break apart the substrate ATP into the products ADP and Pi . ____________________________________________________________________________________ Enzyme Specificity The reaction catalyzed by an enzyme is very specific. Most enzymes are proteins with unique three-dimensional configurations based on their amino acid sequence. The specificity of an enzyme can be attributed to the compatibility between the shape of the enzyme’s active site and the shape of the substrate. Model pieces needed gray foam piece with stickers red D foam piece with stickers tan E foam piece with stickers 1. Place the enzyme model with the sticker side facing up. Write your observation about the active site of the enzyme below. Answers will vary but may include: The active site has a negative charge on the left and a ____________________________________________________________________________________ positive charge on the right. There is a yellow region deep inside the active site. ____________________________________________________________________________________ 2. What might these specialized areas in the enzyme represent? The charged areas represent charged amino acids found in the active site. The yellow region ____________________________________________________________________________________ represents the hydrophobic amino acids in the active site. ____________________________________________________________________________________ 3. What do the red D and tan E foam pieces represent? The red and tan pieces represent possible substrates for the enzyme to act upon. ____________________________________________________________________________________ 4. How do the specialized areas of the red D piece interact with the specialized areas of the enzyme? The positive charge of the enzyme matches with the negative charge of the red piece. The ____________________________________________________________________________________ negative charge of the enzyme matches with the positive charge of the red piece. The yellow ____________________________________________________________________________________ regions match together as well. ____________________________________________________________________________________ 5. In order for enzymes to bind to the correct substrate, enzymes have specific active site configurations that allow for interaction with the substrate. Explain why the tan E substrate would not interact with the enzyme. The tan substrate would not interact with the enzyme because the charged amino acids will ____________________________________________________________________________________ tend to repel and the hydrophobic areas will not interact. ____________________________________________________________________________________ Enzyme Inhibition Model pieces needed gray foam piece with stickers red D foam piece with stickers purple (F) foam piece blue (G) foam piece Competitive Inhibition 1. Place the gray A, red D, purple F and blue G foam pieces on your work surface. Which two pieces may fit into the active site? the red the purple pieces __________________________________ and ___________________________________________ 2. Can the red D substrate bind to the active site if the purple F piece is bound to the enzyme? _______ No. A substance which binds in the active site and prohibits normal substrate interaction is called a competitive inhibitor. 3. Create a sketch using the foam models to illustrate competitive inhibition. competitive inhibitor enzyme active site is blocked substrate can’t bind 4. Predict what might happen in a cell if the concentration of competitive inhibitor exceeded that of the substrate. If the concentration of competitive inhibitor exceeded that of the substrate, the enzyme would ____________________________________________________________________________________ not be able to bind the substrate and the reaction would slow down. ____________________________________________________________________________________ Enzyme Inhibition Noncompetitive Inhibition A noncompetitive inhibitor impedes enzymatic action by binding to another part of the enzyme. This second site, known as the allosteric site, is the place on an enzyme where a molecule that is not a substrate may bind, thus changing the shape of the enzyme and influencing its ability to be active. 5. In the diagram below, draw an “X” where the blue G piece may noncompetitively bind to the enzyme. 6. Sketch what happens to the shape of the enzyme when the blue piece is bound to the allosteric site. noncompetitive inhibitor enzyme active site is altered when noncompetitive inhibitor is bound to enzyme substrate can’t bind due to alteration of the active site 7. How does this affect the binding of the substrate? When the noncompetitive inhibitor is bound to the enzyme, the active site changes shape so ____________________________________________________________________________________ that the substrate is unable to bind to the enzyme. ____________________________________________________________________________________ Activation Energy Activation energy may be defined as the minimum amount of energy required to get the reactants in a chemical reaction to the transition state, in which bonds are broken and new bonds are formed. The activation energy of a reaction is usually denoted by EA. By now you know that enzymes are proteins that catalyze chemical reactions. Enzymes lower the activation energy needed to start a reaction. You may use the foam pieces to simulate the activation energy needed in a reaction with and without an enzyme. Begin by connecting the green foam pieces. To illustrate the activation energy without the enzyme interaction, pull the apart the two green pieces with your hands. Reconnect the green pieces. This time lock them into the active site on the gray A enzyme (without stickers) foam piece. With the help of the enzyme it takes less energy to pull the pieces apart. The activation energy has been lowered! Notice in the graph below that the resulting products have less free energy than the reactants. In such a reaction, energy has been released and the reaction is said to be exothermic. A specific example of an exothermic reaction is the breakdown of hydrogen peroxide into water and oxygen. The enzyme used to facilitate this reaction is known as catalase. 2H O 2H O + O Activation Energy Continues Conversely, in the graph below, the products have more free energy than the reactants. Reactions that absorb heat from the environment are known as endothermic reactions. A common example is a chemical ice pack which typically contains water and a packet of ammonium chloride. To activate the ice pack, the barrier separating the two substances must be physically broken so the two substances may react. Enzymes may also facilitate endothermic reactions. 1. Examine the graph below. Is the reaction depicted exothermic or endothermic? Explain your answer. The reaction in the graph below is endothermic because the products have more energy than ____________________________________________________________________________________ the reactants, indicating that energy has been taken in by the reaction. ____________________________________________________________________________________ The activation energy curve show below represents a non-enzyme catalyzed reaction. 2. Draw a line on the graiph indicating the activation energy in the presences of an enzyme. 3. Which letter depicts the activation energy without the enzyme present? ___________________________________________. B 4. What does the letter ‘E’ represent? Heat absorbed / Endothermic ____________________________________________ ____________________________________________ Lowers activation energy. Activation Energy Continues Post Lab Questions 1. Predict what might happen if enzyme activity were not regulated within a cell’s metabolic pathways. Answers will vary but may include: If enzyme activity were not regulated within a cell’s _____________________________________________________________________________________ metabolic pathways, too much heat may be released in a reaction and the cell may sustain _____________________________________________________________________________________ damage. Additionally, if the enzyme is not working to produce a product, those products may _____________________________________________________________________________________ not be available for the next step in a cascade of reactions. _____________________________________________________________________________________ 2. Contrast the action of a competitive inhibitor with that of a noncompetitive inhibitor. A competitive inhibitor binds in the active site preventing the substrate from interacting with the _____________________________________________________________________________________ enzyme, while a noncompetitive inhibitor binds at another site on the enzyme which changes _____________________________________________________________________________________ the active site preventing the substrate from interacting with the enzyme. _____________________________________________________________________________________ Activation Energy Continues Ethanol is metabolized in the body into acetaldehyde. Normally, acetaldehyde does not accumulate in the body because aldehyde dehydrogenase rapidly oxidizes the acetaldehyde into acetic acid. The drug disulfiram inhibits aldehyde dehydrogenase, which causes an accumulation of acetaldehyde in the body with the subsequent unpleasant side effects of nausea and vomiting. Disulfiram is sometimes used to treat patients with a drinking habit. 3. Create a sketch to illustrate the action of the competitive inhibitor disulfiram. Be sure to label your diagram with the following terms, aldehyde dehydrogenase, disulfiram, acetaldehyde, enzyme, competitive inhibitor, substrate and product. Example only: Student’s answers will vary acetaldehyde (substrate) products: acetic acid (and hydrogen) aldehyde dehydrogenase (enzyme) disulfiram (competitive inhibitor) aldehyde dehydrogenase (enzyme) active site is blocked Activation Energy Continues 4. How is Koshland’s theory of induced fit supported by noncompetitive inhibition of enzymes? Koshland’s theory of induced fit implies that the enzyme must change shape in order to interact _____________________________________________________________________________________ with the substrate. Noncompetitive inhibition occurs when a substance binds to the enzyme at a _____________________________________________________________________________________ site other than the active site while still causing a change in the active site. _____________________________________________________________________________________ 5. Examine the model of the enzyme shown below. Design a competitive and noncompetitive inhibitor for this enzyme. Answers will vary, but the competitive inhibitor should block the active site while the noncompetitive inhibitor blocks the allosteric site. substrate active site enzyme