Chapter 6: Energy and Metabolism Student: 1. Oxidation and reduction reactions are chemical processes that result in a gain or loss in A) atoms. B) neutrons. C) electrons. D) molecules. E) protons. 2. Reactions that occur spontaneously and release free energy are called A) activation reactions. B) exergonic reactions. C) catabolistic reactions. D) thermodynamic reactions. E) end-product reactions. 3. A chemical reaction in which the products contain less energy than the will tend to proceed spontaneously. A) reactants B) enzymes C) coenzymes D) substrates E) cofactors 4. Protein catalysts that speed up the various metabolic biological reactions in an organism are called A) substrates. B) cofactors. C) reactants. D) products. E) enzymes. 5. Enzymes have specific with which they interact. A) products B) substrates C) reactants D) atoms E) end-products 1
6. The specificity of an enzyme is due to its active site. The active site is shaped so that only a certain A) substrate molecule can fit into it. B) product molecule can fit into it. C) reactant molecule can fit into it. D) cofactor molecule can fit into it. E) histone molecule can fit into it. 7. The organic non-protein components that aid in enzyme functioning are called A) reactants. B) cofactors. C) coenzymes. D) substrates. E) products. 8. The inorganic non-protein components that participate in enzyme catalysis are known as A) coenzymes. B) cofactors. C) end-products. D) substrates. E) reactants. 9. The chief energy currency of all cells is a molecule called A) cyclic AMP. B) NADH. C) FADH. D) ATP. E) ADP. 10. The chemistry of living systems representing all chemical reactions is called A) catabolism. B) anabolism. C) metabolism. D) enzymology. E) thermodynamics. 2
11. A calorie is the commonly used unit of chemical energy. It is also the unit of A) light. B) magnetism. C) sound. D) heat. E) radioactivity. 12. The term oxidation is derived from the name of the element oxygen. This is reasonable, because it A) attracts electrons very strongly. B) can be oxidized by accepting electrons. C) contains more electrons than are needed. D) is relatively unreactive (inert). E) is present everywhere. 13. When an atom or molecule gains one or more electrons, it is said to be A) energized. B) oxidized. C) polarized. D) activated. E) reduced. 14. An electron transferred in a biological system is usually A) boosted to a higher light energy state. B) converted into other chemical compounds. C) accompanied by a proton. D) given off as radiant energy. E) lost to the system as heat. 15. Life's ultimate source of energy is derived from A) the sun. B) plants. C) water. D) air. E) cells. 3
16. As energy is being reconverted through the many forms, it is continuously lost as A) electricity. B) light. C) sound. D) heat. E) chemical energy. 17. In reactions of cells the net energy obtained from breaking bonds is called free energy. It is A) the bond energies of reactants. B) the bond energies of products. C) the difference between a and b. D) the amount of energy due to the degree of disorder of the system. E) the amount after d is subtracted from c. 18. Reactions that do not proceed spontaneously because they require energy from an outside source are called A) exergonic. B) xerogonic. C) metabolic. D) endergonic. E) endocytic. 19. Molecules that act as catalysts in biological systems are A) ATP. B) cofactors. C) coenzymes. D) enzymes. E) genes. 20. Enzymes catalyze chemical reactions by lowering the A) entropy. B) free energy. C) activation energy. D) enthalpy. E) calories. 4
21. Biologists studying molecular chemistry and cell evolution have recently discovered cases where cellular processes are catalyzed by molecules that are not proteins. These molecules that are sometimes capable of acting as enzymes are composed of A) fatty acids. B) DNA. C) RNA. D) carbohydrates. E) histones. 22. In an enzyme-catalyzed reaction the reactant is called the A) ribozyme. B) catalyst. C) substrate. D) end-product. E) activator. 23. When the substrate is bound to the enzyme, the shape of the enzyme may change slightly, leading to A) a better induced fit. B) a great range of possible catalytic activities. C) a greater supply of activation energy. D) more permanent binding through intimate total contact. E) more possible products of the reaction. 24. Enzymes are very specific in their choices of substrates because each different enzyme has an active site that A) depends on unusual amino acids not common in proteins. B) has a certain unique amino acid to fit each substrate. C) is shaped to fit a certain substrate molecule. D) is lined with glycolipids and glycoproteins. E) passes electrons from one part of the substrate to another. 25. At the conclusion of an enzyme-catalyzed reaction A) the enzyme must be resynthesized from its amino acids. B) the enzyme frees itself from the product and is ready to be reused. C) the enzyme must be transported from outside of the cell. D) the enzyme's shape is changed into an active form. E) the enzyme's active site closes up and cannot bind to more substrate. 5
26. The sites where molecules other than substrates bind in an enzyme to alter its activity are called A) catalytic sites. B) allosteric sites. C) metabolic sites. D) amino acid sites. E) activity sites. 27. One of the most important coenzymes that accepts electrons/hydrogens is A) NAD+. B) NADH. C) ATP. D) NADPH. E) ribozyme. 28. ATP gives up energy when it is converted to A) DNA. B) NADP. C) NADH. D) ADP and phosphate. E) RNA. 29. Under standard conditions, ATP can release for every molecule A) less than 1 cal of energy. B) 1 to 2 cal of energy. C) 7. 3 Kcal of energy. D) 7. 3 cal of energy. E) different amounts of energy depending on the cell. 30. The regulation of simple biochemical pathways often involves the end-product binding to the allosteric site of the first enzyme in the sequence. This mode of regulation is called A) competitive inhibition. B) biochemical regulation. C) cellular control. D) product catalysis. E) feedback inhibition. 6
31. In an experiment described in a chemistry lab book, the directions state that after mixing the two chemicals (A and B) and waiting 5 minutes that A will be oxidized. This means that A) chemical A has lost electrons to chemical B. B) chemical A has gained electrons from chemical B. C) chemical A has lost its ability to interact with chemical B. D) chemical A has become an isotope and can no longer interact with chemical B. E) chemical A has shared electrons from chemical B. 32. In an experiment described in a chemistry lab book, the directions state that after mixing the two chemicals (A and B) and waiting 5 minutes that B will be reduced. This means that A) chemical B has lost electrons to chemical A. B) chemical B has gained electrons from chemical A. C) chemical B has lost its ability to interact with chemical A. D) chemical B has become an isotope and can no longer interact with chemical A. E) chemical B has shared electrons from chemical A. 33. The First Law of Thermodynamics simply states that A) energy is constantly being created in the universe. B) energy is being lost as heat in the universe. C) energy can be created but not destroyed. D) energy cannot be created or destroyed, just changed from one form to another. E) energy can be recycled through the universe. 34. In a chemical reaction in a living system, enzymes are used as catalysts. All of the following are true of enzymes EXCEPT: A) Enzymes enter reactions and can be reused. B) Enzymes speed up chemical reactions in living systems. C) Enzymes reduce the energy of activation necessary for a chemical reaction to go forward. D) Enzymes increase the energy of activation necessary for a chemical reaction to go forward. E) Enzymes are sometimes referred to as biological catalysts; however, not all biological catalysts are proteins. 7
35. Which of the following best depicts a diagram of enzymes and substrates when they react? Assume only forward reactions. Use the following to make your choice. E = enzyme, S = substrate, ES = enzyme-substrate complex, P = products A) E + P ES B) E + S ES + P C) E + S ES E + P D) E + ES P + E E) E + P EP S + E 36. A new antibiotic has been developed that will use competitive inhibitor enzyme inhibition. This means that the A) antibiotic will compete for substrate binding sites on the enzyme. B) antibiotic will compete for binding sites on the substrate. C) antibiotic will compete for binding sites on the enzyme-substrate complex. D) antibiotic will compete for binding sites on the product that is being produced. E) antibiotic will attach to the enzyme at an area other than the active site. 37. A new antibiotic has been developed that will use noncompetitive inhibitor enzyme inhibition. This means that the A) antibiotic will bind to the active site and alter the shape of the enzyme. B) antibiotic will bind to the substrate and alter the shape of the substrate. C) antibiotic will bind to the enzyme-substrate complex and alter its shape. D) antibiotic will bind to the product that is being produced and alter its shape. E) antibiotic will attach to the enzyme at a position other than the active site. 38. One type of biochemical pathway regulation is referred to as feedback inhibition. This means that as the A) cell produces more quantity of product through a biochemical pathway, the build up of that product will inhibit the activity of that product's production. B) cell produces more quantity of product through a biochemical pathway, the activity will be increased or stimulated by the build up of that product. C) cell produces less quantity of product through a biochemical pathway, the activity will be inhibited by not having enough of that product. D) cell produces less quantity of product through a biochemical pathway, the activity of the substrate will be increased and that it will exceed capacity of the pathway. E) cell produces product, the product behaves as a coenzyme in the reaction. 8
39. The ph of a solution containing an enzyme and its substrate is raised from the optimum of ph 6 to a ph of 8. What would you expect to observe as the result of this change in ph? A) increased rate of disappearance of substrate B) enzyme denaturation C) no significant change in rate of product formation D) decreased rate of disappearance of sustrate E) increased rate of appearance of product 40. Choose the statement that is best associated with the Second Law of Thermodynamics. A) Energy in the universe cannot be created or destroyed. B) As molecules in the universe become more disordered, chemical energy is converted to heat energy. C) Energy is constantly being lost from the universe. D) Molecules spontaneously move from ordered to disordered states. E) Energy can take various forms including light and heat. 9
Use the following to answer questions 41-42: Examine the graphs of two sets of enzyme-catalyzed reactions. 41. The y axis of graph b could represent A) time. B) concentration of enzyme. C) activation energy. D) reaction rate. E) ph. 42. The x axis of graph a could represent A) temperature. B) ph. C) time. D) reaction rate. E) moles of substrate formed. 10
Use the following to answer questions 43-44: A and B represent the same enzyme-catalyzed reaction under different conditions. 43. The curves labeled Reaction A and Reaction B are LEAST likely to be explained by: A) Reaction A contains a greater initial amount of enzyme than reaction B. B) A competitive inhibitor has been added to reaction B. C) Reaction B contains a greater initial amount of substrate than reaction A. D) A noncompetitive inhibitor has been added to Reaction B. E) The reactions are taking place under different ph or temperature conditions. 44. The rates of the reactions appear to slow down over time because: A) the enzyme has been used up. B) the enzyme has become denatured. C) less substrate is available to bind with the enzyme. D) the active site has become overwhelmed by accumulation of product. E) the environment is changed by the removal and addition of the various functional groups. 11
Essay Questions: 45. Discuss three environmental factors that can influence the activity of an enzyme. Using your knowledge of protein structure, explain how these changes occur at the chemical level. 46. Chemical bonds represent stored energy. Explain how oxidation and reduction reactions occur, and the resulting changes to the stored energy held by molecules. 12