WGU Biochem Module 3 Questions

Unit 3 Quiz 1. Which property of enzymes isillustrated in the final step of the enzymatic cycle? a. Enzymes increase the reaction rate for a reaction. b. Enzymes lower the activation energy for a reaction. c. Enzymes are reusable. d. Enzymes are specific. Answer: C. In the final step of the enzymatic cycle, the product is released and the enzyme is able to bind to a new substrate and begin the cycle again. 2. In the enzyme cycle, which step immediately followsinduced fit? a. Formation ofthe enzyme-substrate complex b. Release of the product and enzyme complex c. Formation of the enzyme-molecule complex d. Formation of the enzyme-product complex Answer: D. The induced fit refers to the conformational change that the enzyme undergoes when it binds to the substrate to form the enzyme-substrate complex. Therefore, the enzymatic cycle step that occurs after the induced fit is the formation of the enzyme-product complex. 3. Which type of inhibition occurs when a particular drug binds to the active site of an enzyme? a. Noncompetitive b. Irreversible c. Competitive d. Uncompetitive Answer: C. Competitive inhibitors compete with the substrate to bind to the active site of the enzyme. 4. Salivary amylase, an enzyme responsible for partial digestion of carbohydrates, has optimum activity at a pH value of 6.8. What is the impact on the activity if the pH is decreased to 4.0? a. Significantly increase b. Slightly decrease c. Slightly increase d. Significantly decrease Answer: D. A drop in pH from 6.8 to 4.0 is a significant change in pH. Recall that the hydrogen bonds and ionic bondsthat hold protein structurestogether can be broken by changes in pH. The disruption in protein structure due to this pH change will also significantly decrease amylase activity. 5. Low levels of glutathione are associated with certain types of ovarian and breast cancers. In the synthesis of glutathione, glutathione accumulates in the cell, binding to an enzyme in the pathway and temporarily preventing the synthesis of glutathione. Which type of inhibition is described by this scenario? a. Uncompetitive b. Allosteric c. Feedback d. Competitive Answer: C. The keywords here are that glutathione accumulates and bindsto an enzyme in the pathway to prevent synthesis. Feedback inhibition occurs when a product of a pathway turns into an inhibitor of an enzyme earlier in the pathway. 6. Lipase is an enzyme with an optimum temperature of 98.6°F and an optimum pH of 7.0 in the duodenum in the human body. If a person is experiencing a fever of 99.8°F, what will increase the activity of the lipase enzyme? a. Decrease in temperature b. Increase of pH of duodenum to 8.0 c. Increase in temperature d. Decrease of the substrate of the enzyme Answer: A. An enzyme will have the highest activity when it is under optimal conditions. In this case, the fever of 99.8 is above the optimal temperature,so lowering the temperature will increase activity. Decreasing the substrate of the enzyme would also decrease activity because the substrate is needed to initiate the reaction. 7. The enzyme glucokinase only bindsits substrate glucose and converts glucose into the product glucose-6-phosphate. Which property of enzymes is described by this scenario? a. Reaction rate b. Specificity c. Activation energy d. Induced fit Answer: B. Enzymes have a high degree of specificity. They will bind to one specific class of molecules and usually catalyze only one type of reaction. 8. Low levels of glutathione are associated with neurological, immunological, and cardiovascular impairments. Two enzymatic reactions are involved in the synthesis of glutathione. In the second enzymatic reaction, glutathione synthetase converts glycine to glutathione. What would potentially decrease risks associated with low levels of glutathione? a. Noncompetitive inhibitor of glutathione synthetase b. Uncompetitive inhibitor of glutathione synthetase c. Increasing the amount of glycine in the diet d. Decreasing the amount of glycine in the diet Answer: C. The desired outcome for this scenario is an increase in glutathione. One way to increase glutathione levels is to increase the activity of glutathione synthetase. Glutathione synthetase activity can be increased by increasing the amount of substrate, or glycine available. 9. Which class of enzymes impacts protein function by temporarily removing a phosphate? a. Synthetase b. Esterase c. Phosphatase d. Kinase Answer: C. 10. How doesthe activation energy of enzyme-catalyzed reactions compare to those of corresponding uncatalyzed reactions? a. The activation energy of the enzyme-catalyzed reactions only changesin response to temperature. b. The activation energy of enzyme-catalyzed reactions are lower than the uncatalyzed reaction c. The activation energy of enzyme-catalyzed reactions are the same as uncatalyzed reactions d. The activation energy of enzyme-catalyzed reactions are higher than uncatalyzed reactions Answer: B. The activation energy is the amount of energy needed to get the reaction started and over the energy hill to form products. Enzymes reduce the amount of energy needed to start the reaction or lower the amount of energy needed to climb the energy hill. 11. A final product of a four-step metabolic pathway serves as a noncompetitive inhibitor, binding to an enzyme in this pathway and temporarily turning off the pathway. Which enzyme is most likely to be targeted by the inhibitor? a. The final enzyme in the pathway b. The second enzyme in the pathway c. The first enzyme in the pathway d. Any enzyme in the middle of the pathway Answer: C. The final product’s structure is more unlike the substrate for the first enzyme in the pathway than any other, and thus the least likely to fit the active site of enzyme 1. Additional Practice Questions – Unit 3 1. Which one of the following pathsrequires less activation energy to convert the reactants into the products? The options include the path indicated by a bold line, and the path indicated by a dotted line. a. In presence of an enzyme-Dotted line b. In absence of an enzyme-Bold line Answer: A. The path with the bold line represents the one with the higher amount of energy needed to get the reaction started and over the energy hill to form products, or a higher activation energy. For the path represented by the dotted line, the reactants need less energy to climb the hill, or a lower activation energy, to get the reaction over the hill to form products. 2. Select True or False: the lower the activation energy for a reaction, the faster the reaction rate. True False Answer: True. If less energy is needed to get the reaction over the energy hill, it goes faster. Enzymes help bring all of the items needed for a reaction together in the best way, so less energy is needed for the reaction to get started. This lowers the activation energy for the reaction and speeds up the reaction so that it can go much faster than if the enzyme were not present. 3. How do enzymes eliminate the need for high temperatures to complete a reaction? a. The need for high temperatures is eliminated by increasing the thermal energy needed for the reaction b. The need for high temperatures is eliminated by lowering the activation energy needed for the reaction c. The need for high temperatures is eliminated by increasing the activation energy needed for the reaction d. The need for high temperatures is eliminated by increasing the kinetic energy needed for the reaction Answer: B. Increasing the thermal energy for the reaction would typically result in an increase in the temperature of the reaction. Enzymes function within a certain specific temperature range. The activation energy is the amount of energy the reaction needs to initiate the change of substrate into product. Without an enzyme present, this can be too much energy for the reaction to happen in the body. The enzyme lowers the amount of energy needed by positioning the right amino acids near the right substrate, so less energy is needed when the enzyme is present. This means that the enzyme can function at a lower temperature than would be needed for the reaction if the enzyme were not present. 4. An enzyme that adds a phosphate group is a . An enzyme that removes a phosphate group is known as a . a. phosphatase, kinase b. phosphatase, hydroxylase c. kinase, phosphatase d. kinase, hydroxylase Answer: C. To remember the correct terms, think 'kinases are kind and giving,' and phosphatases take away phosphate groups. 5. Which level of protein structure provides enzymes with theirsubstrate specificity? a. Tertiary structure b. Primary structure c. Quaternary structure d. Secondary structure Answer: A. The tertiary structure of the enzyme is the level that placesthe right amino acids into the right locations in 3D space so that the enzyme can act like a baseball glove and wrap itself around the correct substrate. A baseball glove is designed to catch baseballs, not other types of balls, so it is specific for baseballs. In this way, the enzyme is designed to catch one type of substrate, based on the locations of the R groups of the amino acids in 3D space (tertiary structure), when it wraps up just the right way around the substrate in the active site. 6. Which of the following characteristic of an enzyme is responsible forspeeding up the reaction? a. They can bind multiple substrates b. They catalyze a specific type of reaction c. They are reusable d. They decrease activation energy Answer: D. Enzymes are called catalysts, which means they help speed up a reaction, and they are not used up by the reaction. They have the right amino acids in the right places to help change the substrate into product, and they still have these amino acids when the reaction is over. All of these factors assist the enzyme in lowering the activation energy, which means that less energy isrequired to start the reaction (or get it over the energy hill) than when the enzyme is not present. Therefore, when the enzyme lowers the activation energy this results in a faster reaction. 7. A substrate bindsto an enzyme at a specific site, which is referred to as a(n) . a. Substrate site b. Active site c. Enzymatic site d. Allosteric site Answer: B. Although 'substrate site' seems like it could be a good name, imagine that the enzyme can be activated when the substrate binds in the active site. 8. Which of the following factors can affect the protein folding and activity of an enzyme? a. All of the options are correct b. pH c. Heat d. Reducing agents Answer: A. Heat can disrupt hydrophobic interactions at the center of the protein. pH can disrupt ionic interactions, and hydrogen bonds. Reducing agents can break disulfide bonds. Each of the individual options are correct statements. Therefore, the option 'All of the options are correct' must be chosen to demonstrate your understanding that any of these conditions could disrupt protein folding and activity. 9. Which of the following are possible effect(s) that phosphorylation/dephosphorylation can have on the activity of an enzyme? a. Turn the enzyme "on" or “off” b. Increase enzyme aggregation c. Alter the amino acid sequence of the enzyme d. Increase the amount ofsubstrate for the enzyme. Answer: A. Adding or removing a phosphate group islike 'flipping a switch' on an enzyme's activity. It is a way of modulating, or regulating, enzyme activity. 10. Induced fit describes which of the following? a. An enzyme slightly changesits shape to accommodate specific substrates b. A substrate changes shape to fit the enzyme c. An enzyme changesshape drastically to accommodate all kinds ofsubstrates d. A substrate bound to the enzyme undergoes a slight conformational change to form a product Answer: A. Enzymes have a high degree of specificity. They will bind to one specific class of molecules and usually catalyze only one type of reaction. The enzyme has the right amino acids in the right locations to be able to recognize a particular type of substrate. 11.11. In the figure provided, what component of the enzymatic cycle does the number 3 depict? a. Enzyme and Product b. Enzyme-Substrate Complex c. Enzyme-Product Complex d. Active site Answer: C. First, the substrate and the enzyme come near to each other, and then the substrate can bind to the active site. The binding of the enzyme to the substrate makes the enzyme-substrate complex. After the substrate is changed to product, but before the product's release, the enzyme is still bound to the product, which is called the enzyme-product complex. Last, the enzyme releases the product from its active site. The enzyme is now ready to accept a new substrate molecule and repeat the same steps. 12. What happens to the enzyme at the end of the cycle? a. Remains bound to the product. b. The enzyme is used again. The enzyme will bind to a substrate. c. The enzyme shape is altered and it cannot be re-used for another reaction d. The enzyme is destroyed. Answer: B. During the process of changing the substrate into product and product release, the amino acids in the active site where the chemistry occurred on the substrate are changed back into their original state. This means that, after the product is formed and then released, the same amino acids will then be available to accept the next substrate molecule and repeat the same chemistry. 13. The concept of the induced fit applies to which part of the enzymatic cycle? a. Substrate b. Enzyme-Substrate Complex c. Product d. Enzyme-Product Complex Answer: B. Recent studies on enzymes have shown that while the substrate and active site are somewhat complementary prior to substrate binding, many enzymes will adjust their active site conformation slightly when the substrate binds, and the Enzyme-Substrate complex is formed, to improve the fit. This is known as induced fit. Think about giving a friend a hug. Your arms are wide open as they come towards you, but only when they are next to you do you close your arms around them. Thus, their proximity causes an induced fit with your arms that is a better fit to their body shape than the initial posture of having your arms wide open. Just as you require recognition of your friend prior to embracing them, an enzyme will have some indication from the shape and properties of the molecule, whether it is the correct substrate or not. When the molecule is recognized as the substrate, the enzyme will adjust to form itself around the substrate more tightly to facilitate the reaction it catalyzes. 14. Inhibitors that have a similar structure to a substrate of an enzyme are most likely to bind to the enzyme’s and be a inhibitor. a. Active site, Competitive b. Allosteric site, Competitive c. Active site, Non-competitive d. Allosteric site, Non-competitive Answer: A. Since competitive inhibitors are able to bind the active site of the enzyme in place of the substrate, competitive inhibitors often have a similar structure to the substrate. 15. When an inhibitor binds reversibly to a site of the enzyme that is not the active site, what type of inhibition results? a. Anti-competitive b. Competitive c. Non-competitive d. None of the options Answer: C. Enzymes can be inhibited by substances called non-competitive inhibitors. Some non-competitive inhibitors attach to the enzyme at an allosteric site, which is a site other than the active site.The presence of the non-competitive inhibitor changes the shape of the enzyme enough to interfere with binding of the normal substrate. Some non-competitive inhibitors are used in the regulation of metabolic pathways, but others are poisons. Such inhibitors distort the tertiary protein structure and alter the shape of the active site. Any enzyme molecule thus affected can no longer bind its substrate, so the enzyme cannot catalyze a reaction. Although some non-competitive inhibitors bind reversibly, others bind irreversibly and permanently inactivate the enzyme molecules, thereby greatly decreasing the reaction rate. In non-competitive inhibition, increasing the substrate concentration does not increase the reaction rate as it does in the presence of a competitive inhibitor. 16. You are in charge of designing a drug that inhibits the activity of a specific enzyme. An important criteria for the drug selection is to ensure that the drug directly competes with the original substrate by binding to the active site of the enzyme. Which of the following kind of inhibitor would be an ideal choice? a. Non-specific inhibitor b. Uncompetitive inhibitor c. Competitive inhibitor d. Non-competitive inhibito