Name: Class: Date: Enzyme Practice. Multiple Choice Identify the choice that best completes the statement or answers the question.

Transcription

1 Class: Date: Enzyme Practice Multiple Choice Identify the choice that best completes the statement or answers the question. 1. Which term is used to describe the high-energy intermediate that forms as substrates react at an enzyme s active site? a. Ground state b. Active site c. Activation energy d. Transition state e. Inducing strain 2. If heat speeds chemical reactions in a lab, why can t cells use heat to drive their chemical reactions? a. The high energy costs involved would be prohibitive for the cell. b. Excess heat would speed up all chemical reactions in a nonspecific way and denature proteins. c. Organisms with self-regulated body temperature would actively inhibit increased temperatures. d. Chemical reactions inside cells are much different from chemical reactions in a lab and would not respond to heat in the same way. e. Even heating of the entire cell would be difficult, mainly because cellular contents are not uniformly distributed throughout a cell. 1

2 3. Refer to the table below. Enzyme A catalyzes a cellular reaction found in a wide range of species. The table shows data collected on the turnover numbers of Enzyme A purified from two of these species. In both cases, the same conditions were used to measure turnover numbers. Which statement is consistent with these data? a. ΔG for the two reactions is the same, but the energy of activation for the reaction catalyzed by the mollusk enzyme is lower than the energy of activation for the reaction catalyzed by the bacterial enzyme. b. Energy of activation for the two reactions is the same, but ΔG for the reaction catalyzed by the mollusk enzyme is lower than ΔG for the reaction catalyzed by the bacterial enzyme. c. ΔG for the two reactions is the same, but the energy of activation for the reaction catalyzed by the mollusk enzyme is higher than the energy of activation for the reaction catalyzed by the bacterial enzyme. d. Energy of activation for the two reactions is the same, but ΔG for the reaction catalyzed by the mollusk enzyme is higher than ΔG for the reaction catalyzed by the bacterial enzyme. e. Both energy of activation and ΔG for the reaction catalyzed by the mollusk enzyme are lower than for the reaction catalyzed by the bacterial enzyme. 4. Which statement accurately describes features of the active site of an enzyme? a. The active site shape is specific for the substrates. b. The active site shape is specific for the products. c. The active site is highly versatile and can bind a wide variety of molecules. d. The active site is buried deep within a hydrophobic region of the enzyme. e. The active site takes up the majority of the protein s structure. 5. A particular enzyme catalyzes the conversion of substrate A into product B. If you wished to use this enzyme in a different reaction, the substrate with the best chance of working would be a molecule with the same a. charge as A. b. molecular weight as A. c. atomic composition but different structure as A. d. number of carbons as A. e. three-dimensional shape and charge distribution as A. 2

3 6. Refer to the figure below. A constant amount of enzyme was exposed to increasing amounts of substrate, and the reaction rate was measured at each substrate concentration. The data were plotted in the graph above. How will the data change if the amount of enzyme present in solution was doubled and the measurements repeated? a. The data will form a curve indicating higher reaction rates at low substrate concentrations but eventually reaching the same maximum rate as the one shown. b. The data will form a curve indicating lower reaction rates at low substrate concentrations but eventually reaching the same maximum rate as the one shown. c. The data will form a curve similar to the one shown but leveling off at a maximum rate twice as high. d. The data will form a curve similar to the one shown but leveling off at a maximum rate half as high. e. The graph would not change. 7. Which is a likely explanation for why a cell might downregulate a metabolic pathway? a. The continuous production of a molecule not presently needed by the cell is energetically wasteful. b. The cell can readily obtain the product of the metabolic pathway from the environment. c. The cell needs an intermediate from this metabolic pathway as a component of a separate parallel pathway. d. The product of the metabolic pathway is in low supply and is needed by the cell to maintain the living state. e. Both a and b 8. An inhibitor that binds to the active site of an enzyme is termed a(n) inhibitor, whereas an inhibitor that binds to a site distinct from the active site is termed a(n) inhibitor. These are examples of inhibition. a. competitive; noncompetitive; allosteric b. competitive; uncompetitive; allosteric c. uncompetitive; competitive; reversible d. competitive; noncompetitive; reversible e. competitive; uncompetitive; irreversible 3

4 9. Refer to the table below. A purified enzyme was incubated with various concentrations of a low-molecular-weight carbon-14 labeled Compound X, followed by measurement of the enzyme s catalytic activity. Enzyme samples were passed through a procedure to remove small molecules and then measured for carbon-14 label content. What conclusions can be drawn about how Compound X interacts with this enzyme? a. Compound X is a reversible inhibitor of the enzyme. b. Compound X is a noncompetitive inhibitor of the enzyme. c. Compound X is a competitive inhibitor of the enzyme. d. Compound X is an irreversible inhibitor of the enzyme. e. Both a and c 10. The binding of an effector molecule to one site on an enzyme that causes change in shape of a distant site on the enzyme is a(n) regulator. a. covalent b. ionic c. malleable d. allosteric e. transformative 11. In a cell, a particular enzyme is inhibited by the action of a kinase and activated by the action of a phosphatase. What does this mean? a. The kinase adds a phosphate group to an allosteric site on the enzyme that inhibits the enzyme s catalytic activity; the phosphatase removes the phosphate group and releases this inhibition. b. The phosphatase adds a phosphate group to an allosteric site on the enzyme that inhibits the enzyme s catalytic activity; the kinase removes the phosphate group and releases this inhibition. c. The kinase generates phosphate that binds to the active site of the enzyme, inhibiting its catalytic activity; the phosphatase decomposes phosphate, thereby removing it and its inhibitory effect. d. The phosphatase generates phosphate that binds to the active site of the enzyme inhibiting its catalytic activity; the kinase decomposes phosphate, thereby removing it and its inhibitory effect. e. The kinase binds to one allosteric site on the enzyme, causing a conformational shift that increases catalytic rate; the phosphatase binds to a different allosteric site, causing a conformational shift that decreases catalytic rate. 4

5 12. Refer to the table below. A chemical crosslinker is a molecule with two reactive ends capable of reacting with two different amino acid R groups within one protein molecule or subunit. Chemical crosslinkers can also react with amino acids on two separate subunits within a multisubunit protein. The table above shows catalytic activity data collected for an enzyme under allosteric regulation by glucose. Two samples of enzyme were analyzed, one untreated and the other treated with a chemical crosslinker. Which statement represents a valid interpretation of these data? a. The chemical crosslinker reacted with one or more amino acids at the active site, inhibiting binding of the substrate. b. The chemical crosslinker covalently linked all of the subunits of the enzyme together, which inhibited reactivity of amino acids at the active site. c. The chemical crosslinker locked the enzyme into its fully active conformation that no longer required the binding of glucose. d. The chemical crosslinker locked the enzyme into a conformation that was unable to shift to a less active form in response to glucose binding. e. The chemical crosslinker locked the enzyme into a conformation that was unable to shift to a more active form in response to glucose binding. 13. A biologist studying a metabolic pathway in a fungus species hypothesizes that the pathway is regulated through feedback inhibition. The pathway involves the steps A B C D E. To test his hypothesis, the biologist could test to see whether inhibits the enzyme catalyzing the reaction of. a. E; D E b. A; D E c. E; A B d. B; A B e. D; D E 5

6 14. Two or more enzymes that catalyze the same reaction but differ in amino acid composition and physical properties are known as a. monozymes. b. homozymes. c. isozymes. d. heterozymes. e. chymozymes. 15. Of the enzymes given below, the most likely to maintain catalytic activity during increasing temperature changes from 22 C to 75 C are those isolated from a. bacteria that colonize geyser basins. b. the guts of fish that live in temperate lakes. c. the intestines of mammals. d. a shrimp species that lives in the Arctic Ocean. e. the bloodstreams of tropical birds. 16. Refer to the figure below. The graph shows the change in catalytic reaction rate for an enzyme as a function of temperature. Which statement accurately explains the reasons for the low activity at points A and B? a. At both points A and B, low activity is due to protein denaturation. b. At point A, low activity is due to reduced kinetic energies and collisions of reacting particles at low temperature, whereas low activity at point B is due to protein denaturation. c. At point A, low activity is due to protein denaturation, whereas low activity at point B is due to reduced kinetic energies of reacting particles at a high temperature. d. At both points A and B, low activity is due to temperature-induced conformational shifts in the protein that reduce the affinity of the active site for substrate. e. At both points A and B, low activity is due to reductions in flexibility of the enzyme, which limits its ability to induce strain in the substrate. 6

7 Enzyme Practice Answer Section MULTIPLE CHOICE 1. ANS: D PTS: 1 DIF: 1 2. ANS: B PTS: 1 DIF: 2 3. ANS: A PTS: 1 DIF: 3 BLM: 3. Applying 4. ANS: A PTS: 1 DIF: 1 5. ANS: E PTS: 1 DIF: 2 BLM: 3. Applying 6. ANS: C PTS: 1 DIF: 3 BLM: 3. Applying 7. ANS: E PTS: 1 DIF: 2 8. ANS: D PTS: 1 DIF: 1 9. ANS: A PTS: 1 DIF: 3 BLM: 4. Analyzing 10. ANS: D PTS: 1 DIF: ANS: A PTS: 1 DIF: ANS: E PTS: 1 DIF: 3 BLM: 4. Analyzing 13. ANS: C PTS: 1 DIF: 2 1

8 14. ANS: C PTS: 1 DIF: ANS: A PTS: 1 DIF: 2 BLM: 3. Applying 16. ANS: B PTS: 1 DIF: 3 2