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Chap 01_8e Indicate the answer choice that best completes the statement or answers the question. 1. Hereditary information (with the exception of some viruses) is preserved in: a. deoxyribonucleic acid. b. membrane structures. c. nuclei. d. polysaccharides. e. ribonucleic acid. 2. Accurate folding of a protein does NOT depend on: a. proper pH. b. correct ionic strength. c. correct temperature. d. correct metal ion concentration. e. binding to DNA. 3. What is the correct name for the configuration of the molecule shown?

a. orthogonal b. trans c. cis d. zis e. chiros 4. Which statement is NOT true about the formation of early organisms? a. The first organisms were anaerobic because the atmosphere was devoid of oxygen. b. The original electron donor for photosynthetic processes was probably H2S. c. Oxygen, a powerful oxidant, was probably welcomed by anaerobic organisms as a preferable choice for metabolic reactions. d. The transfer of electrons to O2 releases more energy than transferring electrons to SO42–. e. Cyanobacteria are modern descendants of early photosynthetic oxygen-producers.

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Chap 01_8e 5. Enzymes are biological catalysts that enhance the rate of a reaction by: a. decreasing the activation energy. b. decreasing the amount of free energy released. c. increasing the activation energy. d. increasing the amount of free energy released. e. increasing the energy of the transition state. 6. Which ranking correctly describes the rigidity of the red bond (the central bond) shown in the figure?

a. 2 = most rigid, 3 = least rigid b. 1 = most rigid, 5 = least rigid c. 4 = most rigid, 3 = least rigid d. 2 = most rigid, 1 = least rigid e. 4 = most rigid, 1 = least rigid 7. When Stanley Miller, in Harold Urey's laboratory, subjected a gaseous mixture mimicking the prebiotic atmosphere on Earth to electrical sparks, he found that _____ were formed. a. amino acids b. aldehydes c. ribonucleotides d. both amino acids and aldehydes e. amino acids, aldehydes, and ribonucleotides

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Chap 01_8e 8. In the theory for the origin of life that was tested by Miller and Urey, the prebiotic atmosphere was presumed to: a. already contain some primitive RNA molecules. b. basically be very similar to the atmosphere of today. c. contain many amino acids. d. have an abundance of methane, ammonia, hydrogen, and water. e. be rich in oxygen. 9. An increase in the entropy of a system can be described as an increase in the total amount of _____ of a system. a. kinetic energy b. potential energy c. oxidative energy d. disorder e. heat energy 10. Which statement about living systems is NOT true? a. Living organisms can be described as an open system. b. Living organisms maintain a more or less constant composition at maturity. c. Living systems are in equilibrium with their surroundings. d. Living systems exist in a dynamic steady state. e. Living systems have efficient mechanisms to convert chemical energy from one form into another. 11. The _____ of homologous proteins or genes can be used to estimate the degree of evolutionary relatedness. a. three-dimensional structure b. expression profiles c. sequence similarity d. endosymbiotic nature e. chromosomes 12. The typical three-dimensional structure of a protein in a cell, or _____ conformation, is critical to a protein's function. a. native b. molecular c. chaperone d. macromolecular e. high-affinity

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Chap 01_8e 13. The sum of all the proteins functioning in a cell is the: a. metabolome. b. proteasome. c. lysosome. d. proteome. e. genome. 14. Which discipline uses an approach that tries to understand complex interactions among intermediates and pathways in quantitative terms? a. metabolomics b. genomics c. systems biology d. proteomics e. lipidomics 15. The enzyme fumarase catalyzes the reversible hydration of fumaric acid to L-malate, but it will not catalyze the hydration of maleic acid, which is the cis isomer of fumaric acid. This is an example of: a. biological activity. b. chiral activity. c. racemization. d. stereoisomerization. e. stereospecificity. 16. If a scientist wanted to know whether a particular hydrocarbon was in use in a cell's plasma membrane, they could search the organism's: a. metabolome. b. lipidome. c. glycome. d. proteome. e. genome. 17. If an organism is a facultative anaerobe, which statement is true? a. The organism requires sulfur to live. b. The organism will die if exposed to oxygen. c. The organism requires oxygen to live. d. The organism does not require oxygen to live but will not die if exposed to oxygen. e. The organism requires methane to live.

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Chap 01_8e 18. Which is NOT found in both animal and plant cells? a. ribosome b. Golgi complex c. endoplasmic reticulum d. vacuole e. mitochondrion 19. Which statement is true about genetic mutations? a. Mutations may arise from an unrepaired mistake in DNA replication. b. Mutations may arise from incorrectly repaired damage to one of the DNA strands. c. Mutations in reproductive cells can be passed to offspring. d. Mutations may better equip an organism or cell to survive in its environment. e. All of the statements are true. 20. Which list has the cellular components arranged in order of increasing size? a. nucleotide < DNA < nucleus < chromatin b. nucleotide < DNA < chromatin < nucleus c. nucleotide < chromatin < DNA < nucleus d. DNA < nucleotide < nucleus < chromatin e. DNA < chromatin < nucleus < nucleotide 21. Which element is NOT among the four most abundant in living organisms? a. carbon b. hydrogen c. nitrogen d. oxygen e. phosphorus 22. Which is NOT a property of living organisms? a. precise self-replication b. in a dynamic steady state with the environment c. evolution over time d. composed of cells e. conversion of energy into matter

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Chap 01_8e 23. Which is the major feature that distinguishes eukaryotes from Bacteria and Archaea? a. DNA b. photosynthetic capability c. plasma membranes d. ribosomes e. the nucleus 24. Reaction 1 has a ΔG° of –12.3 kJ/mol, and reaction 2 has a ΔG° of –23.4 kJ/mol. Which statement is true of these two reactions? a. Reaction 1 occurs faster. b. Reaction 2 occurs faster. c. Both reactions occur at the same rate. d. Reaction 2 will not occur. e. It is impossible to know which reaction occurs faster with this information. 25. Which organelle probably originated as an endosymbiotic engulfing of an aerobic bacterium by a eukaryotic cell? a. ribosome b. mitochondrion c. Golgi body d. nucleus e. endoplasmic reticulum 26. In a bacterial cell, the DNA is in the: a. cell envelope. b. cell membrane. c. nucleoid. d. nucleus. e. ribosomes. 27. _____ pathways _____ large molecules, _____ energy. a. Catabolic; break down; releasing b. Anabolic; break down; releasing c. Catabolic; break down; storing d. Anabolic; break down; storing e. Anabolic; build up; releasing

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Chap 01_8e 28. Which statement correctly describes the molecules shown?

a. A and D are enantiomers, and B and C are enantiomers. b. A and D are diastereomers, and B and C are enantiomers. c. A and C are enantiomers, and B and D are diastereomers. d. A and C are diastereomers, and B and D are enantiomers. e. All are diastereomers to each other. 29. Which method is the MOST versatile for separating subcellular components of tissue into fractions containing things ranging from large (e.g., whole cells) to small (e.g., ribosomes)? a. centrifugation b. precipitation c. chromatography d. restriction digest e. peroxidation 30. When two genes share detectable sequence similarity, those genes or their gene products, are said to be: a. homologs. b. symbiologs. c. complimentary sequences. d. co-genes. e. housekeeping genes. 31. Which statement is NOT true regarding the plasma membrane? a. It is a physical barrier separating the inside of the cell from its surroundings. b. It is flexible, with a hydrophobic internal structure. c. The individual lipids and proteins of the plasma membrane are covalently linked. d. The plasma membrane incorporates newly made lipid and protein components as a cell grows. e. Cell division occurs without loss of the membrane integrity. Copyright Macmillan Learning. Powered by Cognero.

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Chap 01_8e 32. Which factor can be changed without breaking covalent bonds? a. conformation b. configuration c. chirality d. stereochemistry e. None of the answers is correct. 33. Stereoisomers that are nonsuperimposable mirror images of each other are known as: a. anomers. b. cis-trans isomers. c. diastereoisomers. d. enantiomers. e. geometric isomers. 34. Which statement is true when Keq >> 1? a. ΔG° is large and negative b. ΔG° is large and positive c. ΔG° is small and negative d. ΔG° is small and positive e. the value of ΔG° is independent of Keq 35. Which is true about a racemic mixture? a. The components are not separable by any means. b. It has no optical rotation. c. It is a mixture of diastereomers. d. It contains both polar and nonpolar substances. e. It can be separated into its components by differential centrifugation. 36. Which group of single-celled microorganisms has many members found growing in extreme environments? a. bacteria b. archaea c. eukaryotes d. heterotrophs e. None of the answers is correct.

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Chap 01_8e 37. The joining of two amino acids via a peptide bond (the process of protein synthesis) has a positive ΔG value. What does this imply? a. Forming a peptide bond is endergonic and must be coupled to another reaction. b. Forming a peptide bond is exergonic and must be coupled to another reaction. c. Forming a peptide bond is spontaneous and does not need to be coupled to another reaction. d. Forming a peptide bond is spontaneous and can sometimes be coupled to another reaction. e. Forming a peptide bond increases the entropy of a system. 38. Which reason is MOST probable for why carbon is the main element used in living organisms? a. Carbon has the simplest isotopic distribution, with no radioactive isotopes. b. Carbon's bonds to other elements are easily formed and broken. c. Carbon has the most valence electrons for its size. d. Carbon has a great capacity to make substances of widely different sizes, shapes, and composition. e. Carbon forms primarily aliphatic compounds. 39. Organisms that derive energy from the oxidation of chemical fuels and require organic compounds as sources of carbon are classified as: a. chemoautotrophs. b. chemoheterotrophs. c. lithotrophs. d. photoautotrophs. e. photoheterotrophs. 40. Which choice correctly lists the molecular masses from smallest to largest? a. 18 kDa < 15,000 Da < 15,100 amu < 1.8 MDa < 1.8 mDa b. 1.8 mDa < 15,000 Da < 15,100 amu < 18 kDa < 1.8 MDa c. 1.8 MDa < 15,000 Da < 15,100 amu < 18 kDa < 1.8 mDa d. 1.8 mDa < 15,100 amu < 15,000 Da < 18 kDa < 1.8 MDa e. 1.8 MDa < 18 kDa < 15,100 amu < 1.8 mDa < 15,000 Da

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Chap 01_8e 41. What functional groups are present on this molecule?

a. ether and aldehyde b. hydroxyl and aldehyde c. hydroxyl and carboxylic acid d. hydroxyl and ester e. hydroxyl and ketone 42. The macromolecules that serve in the storage and transmission of genetic information are: a. carbohydrates. b. lipids. c. membranes. d. nucleic acids. e. proteins. 43. Which statement is true regarding energy sources used by organisms? a. Phototrophs can use carbon dioxide as a carbon source. b. Phototrophs can use carbon dioxide as an energy source. c. All phototrophs are autotrophs. d. All chemotrophs are heterotrophs. e. All phototrophs are autotrophs that can use carbon dioxide as a carbon source. 44. In double-stranded DNA, the two polynucleotide strands are held together by _____ bonds. a. covalent b. ionic c. polypeptide d. hydrogen e. phosphodiester

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Chap 01_8e 45. In supramolecular complexes, macromolecules are held primarily through noncovalent interactions. Which one is NOT considered a noncovalent interaction? a. carbon–carbon bonds b. hydrogen bonds c. hydrophobic interactions d. ionic interactions e. van der Waals interactions 46. When energy is used by a system, can it be "used up"? a. Yes, it is used up when the energy source is depleted. b. Yes, it is used up when all energy is converted into chemical energy. c. No, all energy is converted into potential energy. d. No, all energy is converted into kinetic energy. e. No, energy can be converted into kinetic and potential energy. 47. The four covalent bonds in methane (CH4) are arranged around carbon to give which geometry? a. linear b. tetrahedral c. trigonal bipyramidal d. trigonal planar e. trigonal pyramidal 48. Which does NOT contain a double membrane? a. mitochondrion b. ribosome c. chloroplast d. endoplasmic reticulum e. Golgi body 49. Which present-day observable piece of evidence supports the RNA world hypothesis? a. RNA molecules participate in biologically significant reactions. b. RNA can serve as an information-carrying molecule. c. RNA nucleotides catalyze peptide bond formation. d. RNA molecules participate in biologically significant reactions, and RNA nucleotides catalyze peptide bond formation. e. RNA molecules participate in biologically significant reactions, RNA can serve as an informationcarrying molecule, and RNA nucleotides catalyze peptide bond formation.

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Chap 01_8e 50. In eukaryotes, the nucleus is enclosed by a double membrane called the: a. cell membrane. b. nuclear envelope. c. nucleolus. d. nucleoplasm. e. nucleosome. 51. Jacques Monod wrote, "What is true of E. coli is true of the elephant." What did he mean? a. Bacterial cells are identical to animal cells. b. Bacterial cells can synthesize ivory under certain conditions. c. Bacterial cells have protein repair mechanisms similar to animal cells. d. Bacterial cells contain enzymes similar to those found in animal cells. e. Bacterial cells contain molecules with complexity similar to molecules found in the "mineral world." 52. The similarities of gene sequences and metabolic pathways across the three domains of life are evidence that: a. all modern organisms are derived from a common evolutionary progenitor. b. multiple evolutionary progenitors converged to a single evolutionary model. c. cross-species genetic transfer happens with ease. d. evolution ceases when an organism is successful in its niche. e. All of the above. 53. Which answer choice represents the largest percentage, by weight, of an E. coli cell? a. RNA b. DNA c. protein d. lipids e. water 54. Which is a list of organelles? a. mitochondria, chromatin, endoplasmic reticulum b. peroxisomes, lysosomes, plasma membrane c. proteasomes, peroxisomes, lysosomes d. mitochondria, endoplasmic reticulum, peroxisomes e. All of the answers are correct.

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Chap 01_8e 55. If the free-energy change ΔG for a reaction is –46.11 kJ/mol, the reaction is: a. at equilibrium. b. endergonic. c. endothermic. d. exergonic. e. exothermic. 56. Fructose-1-phosphate can be hydrolyzed into fructose and inorganic phosphate (Pi) with a ΔG° of –16.0 kJ/mol. If ATP can be hydrolyzed into ADP and Pi with a ΔG° of –30.5 kJ/mol, what is the free-energy change for the reaction shown? fructose + ATP → fructose-1-phosphate + ADP a. –46.5 kJ/mol b. –14.5 kJ/mol c. 46.5 kJ/mol d. 14.5 kJ/mol e. –1.45 kJ/mol 57. Energy-requiring metabolic pathways that yield complex molecules from simpler precursors are: a. amphibolic. b. anabolic. c. autotrophic. d. catabolic. e. heterotrophic. 58. _____ are typically expressed under all conditions and are not subject to regulation. a. Housekeeping genes b. Homologous genes c. Bacterial genomes d. Eukaryotic genomes e. Endosymbiotic genes 59. The three-dimensional structure of a protein is determined primarily by: a. electrostatic guidance from nucleic acid structure. b. how many amino acids are in the protein. c. hydrophobic interaction with lipids that provide a folding framework. d. modification during interactions with ribosomes. e. the sequence of amino acids in the protein.

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Chap 01_8e 60. In an oxidation-reduction reaction, the reactant that is oxidized _____, and the reactant that is reduced _____. a. is energized; is de-energized b. is de-energized; is energized c. loses electrons; gains electrons d. gains electrons; loses electrons e. maintains the same number of electrons; loses electrons 61. Which statement is NOT a distinguishing feature of living organisms? a. There exists a high degree of organizational complexity. b. The structure of components influences their function. c. Organisms can reproduce themselves. d. Organisms can exist without interacting with their environment. e. Organisms change over time. 62. Which list of descriptive terms for biological molecules is placed in correct order from smallest to largest? a. monomer, oligomer, polymer b. monomer, multimer, macromer c. oligomer, monomer, polymer d. polymer, oligomer, monomer e. metamer, oligomer, polymer 63. Humans maintain a nearly constant level of hemoglobin by continually synthesizing and degrading it. This is an example of a(n): a. dynamic steady state. b. equilibrium state. c. exergonic change. d. free-energy change. e. waste of energy. 64. Which substance is NOT a secondary metabolite in plants? a. adenine b. morphine c. quinine d. nicotine e. caffeine

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Chap 01_8e 65. Which are the four MOST abundant elements in living organisms? a. carbon, hydrogen, oxygen, iron b. carbon, hydrogen, nitrogen, oxygen c. carbon, hydrogen, phosphorous, oxygen d. carbon, nitrogen, phosphorous, oxygen e. carbon, hydrogen, sulfur, oxygen 66. The major difference between prokaryotes and eukaryotes is that: a. prokaryotes have a nucleus, while eukaryotes do not. b. eukaryotes have a nucleus, while prokaryotes do not. c. eukaryotes have double-stranded DNA, while prokaryotes have single-stranded DNA. d. prokaryotes have double-stranded DNA, while eukaryotes have single-stranded DNA. e. prokaryotes do not have ribosomes. 67. The diagram is a generic example of what process?

a. systems biology b. feedback inhibition c. positive feedback d. equilibrium e. catabolism 68. The breakage of a phosphoanhydride bond in which molecule is a major source of chemical energy to drive cellular reactions? a. acetyl triphosphate b. adenosine monophosphate c. adenosine triphosphate d. cytosine tetraphosphate e. uridine diphosphate

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Chap 01_8e 69. Which types of molecules can serve as informational macromolecules in cells? a. proteins b. nucleic acids c. oligosaccharides d. both proteins and nucleic acids e. proteins, nucleic acids, and oligosaccharides 70. When a region of DNA must be repaired by removing and replacing some of the nucleotides, what ensures that the new nucleotides are in the correct sequence? a. DNA cannot be repaired and this explains why mutations occur. b. Specific enzymes bind the correct nucleotides. c. The new nucleotides base-pair accurately with those on the complementary strand. d. The repair enzyme recognizes the removed nucleotide and brings in an identical one to replace it. e. The three-dimensional structure determines the order of nucleotides. 71. Living cells produce only one chiral form of a biomolecule because: a. biomolecules, by definition, can exist as only one chiral form. b. living cells can only create L isomers. c. living cells choose to express only the correct isomer. d. living cells have enzymes that are also chiral. e. living cells can produce the opposite chiral form only under certain metabolic conditions. 72. Which is the range of typical diameters of animal and plant cells? a. 0.1 μmto 10 μm b. 0.3 μm to 30 μm c. 5 μm to 100 μm d. 10 nm to 300 nm e. 1 μm to 300 μm 73. A chemist working in a pharmaceutical lab synthesized a new drug as a racemic mixture. Why is it important that the chemist separate the two enantiomers and test each for its biological activity?

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Chap 01_8e 74. List and explain the factors that limit the dimensions of living cells on both the lower and upper limits.

75. Describe the RNA world hypothesis.

76. The free-energy change for the formation of a protein from the individual amino acids is positive and is thus an endergonic reaction. How, then, do cells accomplish this process?

77. Describe how the rise of O2-producing bacteria might have led to the eventual predominance of aerobic organisms on Earth.

78. How is chirality generated by an asymmetric carbon atom and why is this important in the study of biochemistry?

79. What is the difference, if any, between cytosol and cytoplasm?

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Chap 01_8e 80. Briefly, compare and contrast the three domains of life.

81. What is meant by the term "in vitro"? What are the challenges and benefits to studying enzymes in vitro?

82. (a) What is the diagram? (b) Describe what it illustrates about the relationship between animals, halophiles, slime mold positive bacteria. (c) Explain the evidence used in construction of this diagram.

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Chap 01_8e 83. Most cells of higher plants have a cell wall outside the plasma membrane. What is the function of the cell wall?

84. Discuss how a mutation in DNA could be harmful or beneficial to an organism.

85. Describe the relationship between a living organism and its surroundings in terms of both matter and energy.

86. What six characteristics distinguish living organisms from inanimate objects?

87. Describe Stanley Miller's experiment (1953) and its relevance.

88. Proteins are constantly being synthesized in a living cell. Why doesn't the number of protein molecules become too great for the cell to contain, leading to cell destruction?

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Chap 01_8e 89. (a) What is optical activity? (b) How did Louis Pasteur arrive at an explanation for the phenomenon of optical activity?

90. Explain the difference, if any, between a proteome and a proteasome.

91. What is the underlying, organizing biochemical principle that results in the chemical similarity of virtually all living things? Given this biochemical similarity, how is the structural and functional diversity of living things possible?

92. Hereditary transmission of genetic information can be viewed as a balance between stability and change. Explain.

93. What is meant by feedback inhibition and why is it important in a living organism?

94. Draw the structures of the functional groups in their nonionized forms for (a) hydroxyl, (b) carboxyl, (c) amino, (d) phosphoryl.

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Chap 01_8e 95. Explain why living organisms are able to produce particular chiral forms of different biomolecules while laboratory chemical synthesis usually produces a racemic mixture.

96. E. coli is known as a gram-negative bacterial species. (a) How is this determined? (b) How do gramnegative bacteria differ structurally from gram-positive bacteria?

97. Differentiate between configuration and conformation.

98. Instant cold packs get cold when the contents, usually solid urea and liquid water, are mixed, producing an aqueous solution of urea. Although this process is clearly spontaneous, the products are colder than the reactants. Explain how this is possible in terms of the difference between ΔG and ΔH.

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Chap 01_8e 99. (a) On the reaction coordinate diagram, label the transition state and the overall free-energy change (ΔG) for the uncatalyzed reaction A→B. (b) Is this an exergonic or endergonic reaction? (c) Draw a second curve showing the energetics of the reaction if it were enzyme-catalyzed.

100. Provide a brief explanation for the observation that macromolecules diffuse at a slower rate in the cytosol than they do in dilute solution.

101. How is the genetic information encoded in DNA, and how is a new copy of DNA synthesized?

102. What is meant by endosymbiotic association? How can this concept explain the evolution of eukaryotic cells that are capable of carrying out photosynthesis and/or aerobic metabolism?

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Chap 01_8e 103. All cells are surrounded by a plasma membrane composed of lipid and protein molecules. What is the function of the plasma membrane?

104. Name two functions of (a) proteins, (b) nucleic acids, (c) polysaccharides, (d) lipids.

105. (a) List the types of noncovalent interactions that are important in providing stability to the three-dimensional structures of macromolecules. (b) Why is it important that these interactions be noncovalent, rather than covalent, bonds?

106. Why is the use of the expression Mr = 18,000 daltons incorrect?

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Chap 01_8e Answer Key 1. a 2. e 3. c 4. c 5. a 6. c 7. d 8. d 9. d 10. c 11. c 12. a 13. d 14. c 15. e 16. b 17. d 18. d 19. e 20. b 21. e 22. e 23. e 24. e 25. b 26. c Copyright Macmillan Learning. Powered by Cognero.

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Chap 01_8e 27. a 28. a 29. a 30. a 31. c 32. a 33. d 34. a 35. b 36. b 37. a 38. d 39. b 40. b 41. b 42. d 43. a 44. d 45. a 46. e 47. b 48. b 49. e 50. b 51. d 52. a 53. e 54. d Copyright Macmillan Learning. Powered by Cognero.

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Chap 01_8e 55. d 56. b 57. b 58. a 59. e 60. c 61. d 62. a 63. a 64. a 65. b 66. b 67. b 68. c 69. e 70. c 71. d 72. c 73. Biomolecules such as receptors for drugs are stereospecific, so each of the two enantiomers of the drug may have very different effects on an organism. One may be beneficial, the other toxic; or one enantiomer may be ineffective and its presence could reduce the efficacy of the other enantiomer. 74. On the lower end, cell dimensions are limited by the minimum number of biomolecules necessary for function. On the upper end, cells are limited by the rate of diffusion of solutes such as oxygen. 75. Initially, RNA molecules were both genes and catalysts. Self-replication of these molecules over long periods of time produced variants that were able to catalyze polymerization of amino acids to form peptides that assumed the function of catalysts. Eventually, genomic RNA was copied into DNA, which assumed the function of genetic information storage. 76. The endergonic (thermodynamically unfavorable) reaction is coupled to an exergonic (thermodynamically favorable) reaction through a shared intermediate, so that the overall free-energy change of the coupled reactions is negative (the overall reaction is exergonic).

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Chap 01_8e 77. The rise of O2-producing bacteria would result in an increase in the levels of O2 in Earth's atmosphere. This would give a selective advantage to aerobic organisms (which utilized O2 as electron acceptor) over anaerobic organisms for which O2 was toxic. 78. An asymmetric carbon has four different substituents attached, and cannot be superimposed on its mirror image, just as a right hand cannot fit into a left glove. Thus, a molecule with one asymmetric (chiral) carbon will have two stereoisomers, which may be distinguishable from one another in a biological system. 79. The cytoplasm is the internal volume enclosed by the plasma membrane; the cytosol is the aqueous portion of the cytoplasm. 80. Bacteria and Archaea consist of unicellular organisms, while Eukarya contains both single- and multicellular organisms. Bacteria and Archaea have been found in all kinds of environments. Archaea historically were characterized from extreme environments. Neither bacteria nor archaea have chromosomes separated from the cytoplasm by a nuclear membrane, but eukaryotes have chromosomes inside a membrane-bounded nucleus. 81. "In vitro" means "in glass"—in the test tube. Challenges include that the experiment may not include all of the molecules that influence an enzyme's activity, the rate of reaction may differ from in vivo due to concentration and crowding/diffusion effects. Benefits include that the enzyme activity is isolated from interfering components, and that the reaction takes place in a thoroughly stirred solution. 82. (a) This diagram is a phylogenetic tree. (b) It illustrates the evolutionary distance between different organisms in the three domains of life. Of the organisms listed, animals are most closely related to slime molds, next closest to halophilic archaea. Archaea and Eukarya are more similar to each other than either is to Bacteria, making grampositive bacteria the most distant relative to all of the organisms listed in this question. (c) The distances between the branches of the tree are calculated by comparing sequence similarity between homologous proteins in different organisms. 83. The cell wall provides a rigid, protective shell for the cell. It is porous, allowing water and small molecules to pass readily, but it is rigid enough to resist the swelling of the cell caused by the accumulation of water (see Fig. 1-8). 84. Some mutations lead to the synthesis of an inactive or defective enzyme or other protein that can no longer carry out its proper function, which is thus harmful to the organism. However, other mutations may lead to a more stable enzyme or to a protein that is better able to carry out its function in a particular environment, making it beneficial to the organism. 85. Living organisms are open systems and exchange both matter and energy with their surroundings. They are not at equilibrium with their surroundings; that is, the exchange of matter and energy with the surroundings is not constant and equal in both directions. To maintain this situation, the organism must acquire energy from its surroundings, either in the form of chemical energy or directly from sunlight. 86. Living organisms (1) are chemically complex and highly organized; (2) extract, transform, and use energy from their environment; (3) have the capacity to precisely self-replicate and self-assemble; (4) exploit a chemical interplay with their environment; (5) possess programmatically defined functions; and (6) evolve to new forms over many generations.

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Chap 01_8e 87. Miller subjected a gaseous mixture of ammonia, methane, water vapor, and hydrogen to electrical sparks for periods of a week or more. When he analyzed the contents of the closed reaction vessel, the gas phase contained CO and CO2, as well as unreacted starting materials. The water phase contained a variety of organic compounds, including some amino acids, hydroxy acids, aldehydes, and hydrogen cyanide. This experiment established the possibility of abiotic production of biomolecules in relatively short times under relatively mild conditions. 88. The proteins in a cell are continuously being synthesized and degraded. The cell maintains a dynamic steady state in which the amount of each protein remains fairly constant at the level required under given conditions. 89. (a) Optical activity is the capacity of a substance to rotate the plane of plane-polarized light. (b) Using fine forceps, he was able to separate the two types of crystals found in tartaric acid (racemic acid) that are identical in shape, but mirror images of each other. One sample rotated polarized light to the left; the mirror image crystals rotated polarized light to the right. 90. A proteome is the list of all proteins that function in a given cell. A proteasome is a molecular machine or supramolecular structure responsible for protein degradation in a cell. 91. Living things are composed primarily of macromolecules, polymers of simple compounds of just a few different types. The properties of these polymers are determined by their sequence of monomers and these can be combined in many different ways. Diversity is thus achieved through the nearly limitless variety of sequences that can exist when amino acids are linked to form proteins, nucleotides are linked to form nucleic acids, and monosaccharides are linked to form polysaccharides. Branching in the latter can contribute additional heterogeneity. Each type of organism constructs a unique set of macromolecules from these monomeric units, resulting in the structural and functional diversity among species. 92. Hereditary transmission of genetic information occurs via replication of DNA, the information-containing molecule. This process is very accurate and thus results in relatively few changes in genetic information. This stability is important to maintain individual and species characteristics over long periods of time. On the other hand, regular changes in genetic information (mutations) do occur, primarily as a result of infrequent errors in replication. These mutations are essential for generating genetic diversity, which allows for adaptation of species. 93. feedback inhibition is the regulation of a biochemical pathway in which a reaction product inhibits an earlier (usually the first) step in the pathway. It is an important type of regulation because it ensures that energy is not wasted by an organism producing molecules it does not need.

94. 95. Laboratory syntheses usually use achiral reagents and thus produce racemic mixtures of products. In contrast, because all enzymes are made of chiral precursors, all enzymes are inherently chiral catalysts. Thus, they will show strong stereoselectivity in reactants and mechanisms, leading to the production of chiral products. Copyright Macmillan Learning. Powered by Cognero.

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Chap 01_8e 96. (a) Gram-negative bacteria have little affinity for the dye gentian violet used in Gram's stain, but gram-positive bacteria retain Gram's stain. (b) Gram-negative bacteria have an outer membrane and a peptidoglycan layer; gram-positive bacteria lack an outer membrane and the peptidoglycan layer is much thicker. 97. Configuration denotes the spatial arrangement of the atoms of a molecule that is conferred by the presence of either double bonds or rings, around which there is no freedom of rotation, or chiral centers, which give rise to stereoisomers. Configurational isomers can only be interconverted by temporarily breaking covalent bonds. Conformation refers to the spatial arrangement of substituent groups that, without breaking any bonds, are free to assume different positions in space because of the freedom of bond rotation. 98. Since the dissolution reaction is spontaneous, the ΔG must be negative. Since the reaction absorbs heat, the ΔH must be positive. Given ΔG = ΔH – TΔS, this is possible if the ΔS is very large and positive, as one would expect for a solid dissolving. 99. (a) and (c) see Fig. 1-28 (b) exergonic reaction 100. The cytosol is very crowded and gel-like. The diffusion of macromolecules is slowed by collisions with other large molecules and structures. 101. The genetic information is encoded in the linear sequence (order) of the four different deoxyribonucleotides in the DNA. When a new copy of DNA is needed, the two strands of the DNA unwind and each strand serves as a template on which a new strand is synthesized. 102. An endosymbiotic association is the envelopment of one organism by another to form a relationship that is beneficial to both organisms. It is believed that primitive eukaryotic cells, which were incapable of photosynthesis or aerobic metabolism, formed endosymbiotic associations with photosynthetic and/or aerobic bacteria. The aerobic bacteria then evolved into the mitochondria found in modern eukaryotic cells, and the photosynthetic bacteria evolved into the chloroplasts found in plant cells (see Fig. 1-37). 103. The plasma membrane acts as a barrier to the free passage of inorganic ions and most other charged or polar compounds into or out of the cell. It contains proteins that can transport specific ions or molecules. Other membrane proteins act as receptors that transmit signals from the outside to the inside of the cell. 104. Many answers are possible including: (a) proteins function as enzymes, structural elements, signal carriers, transporters; (b) nucleic acids store and transmit genetic information and act as both structural and catalytic elements; (c) polysaccharides serve as energy-yielding fuel stores and cellular and extracellular structural and recognition elements; (d) lipids function as membrane components, fuel stores, and cellular signals. 105. (a) Noncovalent interactions include hydrogen bonds, ionic interactions between charged groups, van der Waals interactions, and hydrophobic interactions. (b) Because noncovalent interactions are weak, they can form, break, and re-form more rapidly and with less energy input than can covalent bonds. This is important to maintain the flexibility needed in macromolecules. 106. Mr is a ratio and therefore dimensionless. Daltons are only used when describing molecular mass, not molecular weight or relative molecular mass.

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Chap 02_8e Indicate the answer choice that best completes the statement or answers the question. 1. The hydrophobic effect makes important energetic contributions to: a. binding of a hormone to its receptor protein. b. enzyme-substrate interactions. c. membrane structure. d. three-dimensional folding of a polypeptide chain. e. All of the answers are correct. 2. Which statement is true about the hydrophobic effect? a. It is the driving force in the formation of micelles of amphipathic compounds in water. b. It does not contribute significantly to maintaining the native conformation of water-soluble proteins. c. Hydrophobic effect interactions have bonding energies of approximately 20 to 40 kJ/mol. d. The hydrophobic effect involves interaction with water to denature proteins. e. The hydrophobic effect primarily determines the solubility of polar solutes. 3. A compound is known to have two ionizable groups: a free amino group with a pKa of 8.8, and another group with a pKa between 5 and 7. A mixture of 100 mL of a 0.2 M solution of this compound at pH 8.2 and 40 mL of 0.2 M hydrochloric acid has a final pH of 6.2. What is the pKa of the second ionizable group? a. The pH cannot be determined from this information. b. 5.4 c. 5.6 d. 6.0 e. 6.2 4. Which would have the greatest effect on osmotic pressure? a. 1 M NaCl (molecular weight = 58 g/mol) b. 1 M CaCl2 (molecular weight = 111 g/mol) c. 1 M glucose (molecular weight = 180 g/mol) d. 1 M sucrose (molecular weight = 342 g/mol) e. All of the answer choices would have the same effect. 5. When two atoms are joined together covalently, the van der Waals radius of the atoms in the covalent bond are _____ than the radius of the atoms alone because the joined atoms are _____. a. shorter; pulled together by the shared electron pair b. shorter; pulled together by the attraction of the nucleus to the bonded atom c. shorter; pulled together by hydrogen bonding d. longer; repelled due to the shared electron pair e. longer; repelled due to the nuclear repulsion between bonded atoms Copyright Macmillan Learning. Powered by Cognero.

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Chap 02_8e 6. What is the pH of a 0.1 M NaOH solution? a. 0.1 b. 1.0 c. 12.8 d. 13 e. 14 7. Distilled white vinegar has a pH of 2.4. What is the [H+] of distilled white vinegar? a. 2.4 M b. 2.5 × 10–12 M c. 2.5 × 10–3 M d. 3.98 × 10–3 M e. 3.98 × 10–6 M 8. The pH of a sample of blood is 7.4, while gastric juice is pH 1.4. The blood sample has _____ [H+] than the gastric juice. a. 0.189 times the b. 5.29 times lower c. 6 times lower d. 6,000 times lower e. one million times lower 9. When water is found bound in the internal structure of a biomolecule, which statement is false? a. The properties of the bound water molecules are different from those of the "bulk" water of the solvent. b. The bound water molecules may provide a path for proton hopping. c. The bound water molecules may form an essential part of the protein's ligand-binding site. d. The orientation of bound water molecules is precise. e. None of the above; all of the statements are true. 10. Which statement does NOT describe a strategy used by multicellular animals to maintain osmotic balance with their surroundings? a. Cells have a contractile vacuole, an organelle that pumps water out of the cell. b. Animals have a high concentration of albumin and other proteins in blood plasma. c. Cells actively pump out Na+ and other ions. d. Cells store fuel as a polysaccharide instead of as simple sugars. e. All of the statements describe a strategy to maintain osmotic balance.

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Chap 02_8e 11. If a person is suffering from mild acidosis, which treatment/action would help counteract the acidosis the most? a. intravenous administration glucose b. deep breathing c. breathing into a paper bag d. vigorous exercise e. All of these treatments/actions could be used to counteract acidosis. 12. Which diagram correctly illustrates the clustering of lipids in the formation of a micelle?

a. A b. B c. both A and B d. neither A nor B 13. Which is the conjugate base of H2PO41–? a. H3PO4 b. H2PO42– c. HPO42– d. HPO43– e. PO43– 14. If the pH of a solution is 5.5, what is the pOH? a. 8.5 b. –5.5 c. –8.5 d. 14 e. 6.5

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Chap 02_8e 15. Which force plays the greatest role in stabilizing biological membranes? a. hydrogen bonding because it a strong noncovalent bond b. hydrophobic interactions that increase solvent entropy c. covalent interactions because they are very stable interactions d. electrostatic interactions between oppositely charged ions e. van der Waals interactions because of the attraction between transient dipoles 16. According to the titration curve shown, acid A is _____ because the pH _____.

a. weak; resists change when 50% titrated b. strong; resists change when 50% titrated c. weak; changes dramatically when 50% titrated d. strong; changes dramatically when 50% titrated e. It cannot be determined from the information given.

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Chap 02_8e 17. A 1.0 M solution of a compound with two ionizable groups (pKa values = 6.2 and 9.5; 100 mL total) has an initial pH of 6.8. If a biochemist adds 60 mL of 1.0 M HCl to this solution, what is the final pH? a. 5.60 b. 8.90 c. 9.13 d. 9.32 e. The pH cannot be determined from this information. 18. List the acids in increasing order of strength (weakest to strongest): nitrous acid (Ka = 4.0 × 10–4), carbonic acid (Ka = 4.4 × 10–7), acetic acid (Ka = 1.7 × 10–5), phosphoric acid (Ka = 7.3 × 10–3). a. acetic acid, carbonic acid, nitrous acid, phosphoric acid b. carbonic acid, acetic acid, nitrous acid, phosphoric acid c. acetic acid, nitrous acid, carbonic acid, phosphoric acid d. phosphoric acid, nitrous acid, acetic acid, carbonic acid e. carbonic acid, phosphoric acid, nitrous acid, acetic acid 19. Three buffers are made by combining a 1 M solution of acetic acid with a 1 M solution of sodium acetate in the ratios shown. 1 M acetic acid 1 M sodium acetate Buffer 1: 10 mL 90 mL Buffer 2: 50 mL 50 mL Buffer 3: 90 mL 10 mL Which statement is true of the resulting buffers? a. pH of buffer 1 < pH of buffer 2 < pH of buffer 3 b. pH of buffer 1 = pH of buffer 2 = pH of buffer 3 c. pH of buffer 1 > pH of buffer 2 > pH of buffer 3 d. The problem cannot be solved without knowing the value of pKa. e. None of the statements is true. 20. According to the Henderson-Hasselbalch equation, when is the pH equal to the pKa? a. when the concentration of acid is close to zero b. when the pH approaches 7 c. when the concentration of the conjugate base is equal to the ionization constant for water d. when the concentration of the conjugate base is equal to the concentration of the acid e. None of the answers is correct.

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Chap 02_8e 21. Which statement correctly describes the situation of the cell in the diagram? The black dots represent solute molecules.

a. The cell is in a hypotonic solution; water will move into the cell and cause it to swell. b. The cell is in a hypotonic solution; solute will move into the cell and cause it to swell. c. The cell is in a hypotonic solution; water will move out of the cell and cause it to shrink. d. The cell is in a hypertonic solution; solute will move into the cell and cause it to swell. e. The cell is in a hypertonic solution; water will move out of the cell and cause it to shrink.

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Chap 02_8e 22. Ibuprofen is a weak acid with a pKa of 4.9 (structure is shown with the ionizable hydrogen marked with a star). Ibuprofen is absorbed through the stomach and the small intestine. In these tissues, absorption is a function of polarity. Charged and very polar molecules are absorbed slowly; neutral hydrophobic molecules absorb quickly. If the stomach pH is about 1.5 and the small intestine pH is about 6, where (and why) will more ibuprofen be absorbed into the bloodstream?

a. More ibuprofen will be absorbed in the small intestine because it will be uncharged due to the pH being greater than the pKa. b. More ibuprofen will be absorbed in the stomach because it will be uncharged due to the pH being lower than the pKa. c. More ibuprofen will be absorbed in the small intestine because it will be charged due to the pH being greater than the pKa. d. More ibuprofen will be absorbed in the stomach because it will be charged due to the pH being lower than the pKa. e. Ibuprofen will be absorbed equally well in both the stomach and small intestine. 23. Which list correctly shows bond/interaction strength in decreasing order (strongest to weakest)? a. covalent bond > hydrogen bond > ionic bond > van der Waals interaction b. covalent bond > ionic bond > hydrogen bond > van der Waals interaction c. ionic bond > covalent bond > hydrogen bond > van der Waals interaction d. covalent bond > van der Waals interaction > ionic bond > hydrogen bond e. hydrogen bond > ionic bond > van der Waals interaction > covalent bond

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Chap 02_8e 24. What is the pH of a 1 M HCl solution? a. 0 b. 0.1 c. 1 d. 10 e. –1 25. A hydronium ion is: a. H3O+. b. immediately formed when hydrogen ions are released in water. c. a hydrated proton. d. formed by the dissociation of water. e. All of the answers are correct. 26. Formic acid is in the venom of some ant species. What is the pH of a 0.2 M solution of formic acid (Ka = 1.78 × 10–4 M)? a. 8.90 b. 4.45 c. 3.75 d. 2.2 e. 1.72 27. The OH– concentration of a solution is 4.3 × 10–10 M. What is the pH? a. –9.37 b. 9.37 c. –4.63 d. 4.63 e. 13.4

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Chap 02_8e 28. According to the titration curve shown, what is a good buffering range for acid A?

a. 0.3 M to 0.8 M OH– b. 0.9 M to 1.0 M OH– c. pH 3.5 to pH 4.2 d. pH 2.8 to pH 3.8 e. pH 2.8 to pH 4.8 29. An example of osmosis is movement of a _____ molecule across a membrane. a. charged solute b. gas c. nonpolar solute d. polar solute e. water 30. Which statement about hydrogen bonds is false? a. Hydrogen bonds are highly directional. b. Hydrogen bonds are capable of holding molecules in a specific geometric arrangement. c. Hydrogen bonds are strongest when the three atoms in the bond are in a straight line. d. Hydrogen bonds are strongest when the oxygen atom is perpendicular to the hydrogen donor. e. Hydrogen bonds place a hydrogen with a partial positive charge directly between two atoms with partial negative charges. Copyright Macmillan Learning. Powered by Cognero.

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Chap 02_8e 31. Which correctly represent hydrogen bonding?

a. A and D b. A and C c. B and C d. C and D e. B and D 32. Which statement correctly describes the forces that drive the formation of micelles by amphipathic molecules, such as fatty acids, dissolved in water? a. Head groups of the molecules are sequestered in the interior of the micelle, maximizing hydrogen bonding of the hydrophobic tail with surrounding solvent molecules. b. Head groups of the molecules are exposed on the outer surface of the micelle, maximizing hydrogen bonding between hydrophobic tails. c. Head groups of the molecules are exposed on the outer surface of the micelle, minimizing the order of the surrounding water molecules. d. Hydrophilic tails are exposed on the outer surface of the micelle, maximizing hydrogen bonding between the tails and surrounding water molecules. e. Hydrophobic tails are exposed on the outer surface of the micelle, maximizing hydrogen bonding between head groups. 33. Adding a solute to water lowers the freezing point of water. The solute changes this colligative property of water by _____ the water. a. lowering the concentration of b. increasing hydrogen bonding in c. altering the ionic bonding within d. changing the pH of e. changing the temperature of

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Chap 02_8e 34. If the Ka of an acid is 1.38 × 10–7, what is the pKa? a. 6.86 b. 7.14 c. 4.37 d. 10.7 e. 1.38 35. Which statement about buffers is true? a. A buffer composed of a weak acid of pKa = 5 has greater buffering capacity at pH 4 than at pH 6. b. At pH values lower than the pKa, the conjugate base concentration is higher than that of the conjugate acid. c. The pH of a buffered solution remains constant no matter how much acid or base is added to the solution. d. The best buffers are those composed of strong acids and strong bases. e. When pH = pKa, the weak acid and conjugate base concentrations in a buffer are equal. 36. Milk of magnesia has a pH of 10.2. What is the [OH– ] of milk of magnesia? a. 6.31 × 10–11 M b. 1.58 × 10–4 M c. 1.58 × 10–5 M d. 1.02 × 10–3 M e. 6.31 × 10–4 M 37. Phosphoric acid is tribasic, with three pKa values: 2.14, 6.86, and 12.4. Which ionic form predominates at pH 4.5? a. H3PO4 b. H2PO4– c. HPO42– d. PO43– e. None of the answers is correct.

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Chap 02_8e 38. "Proton hopping" essentially means that: a. an individual proton jumps from one electronegative group to the next. b. a free proton moves from one hydroxyl group of ionized water to the next. c. several protons move between hydrogen-bonded water molecules causing the net movement of a proton over a long distance in a short time. d. individual protons are freer to move among and between water molecules in solution. e. hydronium ions are freer to move among and between water molecules in solution. 39. Which statement about hydrogen bonds is NOT true? a. Hydrogen bonds account for the high boiling point of water compared to molecules of similar size. b. In liquid water, the average water molecule forms hydrogen bonds with three to four other water molecules. c. Individual hydrogen bonds are much weaker than covalent bonds. d. Individual hydrogen bonds in liquid water exist for many seconds and sometimes for minutes. e. The strength of a hydrogen bond depends on the linearity of the three atoms involved in the bond. 40. Which process would NOT disrupt the weak interactions between two biomolecules in solution? a. heating the solution b. cooling the solution c. lowering the pH of the solution d. increasing the ionic strength of the solution e. All of the answer choices would disrupt interactions between biomolecules. 41. The aqueous solution with the highest pH is: a. 1 M HCl. b. 1 M NH3 (pKa = 9.25). c. 0.5 M NaHCO3 (pKa = 3.77). d. 0.1 M NaOH. e. 0.001 M NaOH.

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Chap 02_8e 42. Which diagram illustrates an amphipathic molecule?

a. A b. B c. C d. D 43. When a nonpolar solute is dispersed in water, which will occur? a. the entropy of the water decreases b. the entropy of the water increases c. the enthalpy of solution is negative d. the system reaches equilibrium quickly e. All of the answers are correct.

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Chap 02_8e 44. Polar molecules cannot easily pass through the cell membrane, but hydrophobic molecules can easily pass through the membrane. Both molecules shown can raise blood pressure. Compare the molecules and select the statement that is true.

a. Ephedrine can more easily pass through the cell membrane than epinephrine. b. Epinephrine can more easily pass through the cell membrane than ephedrine. c. Both epinephrine and ephedrine can pass through the cell membrane equally well. d. Neither epinephrine nor ephedrine can pass through the cell membrane. e. None of the statements is true. 45. Which statement regarding long-chain fatty acids in aqueous solution is NOT true? a. Fatty acids in small concentrations are surrounded by highly ordered water molecules in a cagelike structure. b. Fatty acids will cluster together to minimize the lipid surface area. c. Fatty acids will form micelles to sequester hydrophobic groups from water. d. The driving force of solubilizing fatty acids is increasing entropy of the fatty acid. e. All of the statements are true. 46. A 0.6 M solution of a weak acid had a pH of 5.8. What is the pKa of the weak acid? a. 11.3 b. 10.5 c. 8.2 d. 5.7 e. 2.9

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Chap 02_8e 47. The objective is to maintain pH = 7.0 for an enzyme-catalyzed reaction that will produce hydrogen ions along with the desired product. At equal concentrations, which weak acid, if any, will serve as the better buffer for the reaction: acid A with pKa = 6.5, or acid B with pKa = 7.5? a. acid A b. Water is as good as either of the acids available. c. acid B d. Both are equally effective. 48. Which statement is true about the properties of aqueous solutions? a. A pH change from 5.0 to 6.0 reflects an increase in the hydroxide ion concentration, [OH– ], of 20%. b. A pH change from 8.0 to 6.0 reflects a decrease in the proton concentration, [H+], by a factor of 100. c. Charged molecules are generally insoluble in water. d. Hydrogen bonds form readily in aqueous solutions. e. The pH can be calculated by adding 7 to the value of the pOH. 49. Which answer choice is involved in important biological buffering systems? a. histidine b. bicarbonate c. phosphate d. bicarbonate and phosphate e. histidine, bicarbonate, and phosphate 50. Ice is _____ dense than water because _____. a. less; frozen water maintains more hydrogen bonds than liquid water b. less; liquid water maintains more hydrogen bonds than frozen water c. more; frozen water maintains more hydrogen bonds than liquid water d. more; liquid water maintains more hydrogen bonds than frozen water e. more; frozen water cannot hydrogen bond 51. Which contributes to water's unusual properties? a. the geometry of water molecules b. the polarity of water c. the ability of water molecules to hydrogen bond d. the electronegativity of the oxygen in water e. All of the answers are correct.

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Chap 02_8e 52. Substance X has a pKa of 7.4. What is the pH of the final solution formed by mixing 100 mL of a 1.0 M solution of X that is initially at pH 8.0 and 30 mL of 1.0 M hydrochloric acid? a. 6.5 b. 6.8 c. 7.2 d. 7.4 e. 7.5 53. Which compound is a diprotic acid? a. CH3COOH b. NH4+ c. H2CO3 d. H3PO4 e. CH3CH2OH 54. The H+ concentration of a solution is 5.6 × 10–5 M. What is the pH? a. –4.25 b. 4.25 c. 5.65 d. –9.75 e. 9.75 55. The aqueous solution with the lowest pH is: a. 0.01 M HCl. b. 0.1 M acetic acid (pKa = 4.86). c. 0.1 M formic acid (pKa = 3.75). d. 0.1 M HCl. e. 10–12 M NaOH. 56. Oxygen and carbon dioxide are both biologically important gases. Which statement about these gases is true? a. O2 and CO2 are both nonpolar and are very soluble in water. b. O2 and CO2 are both polar and are very soluble in water. c. O2 and CO2 are both nonpolar and are poorly soluble in water. d. CO2 contains polar bonds and is very soluble in water, but O2 is nonpolar and is poorly soluble in water. e. O2 contains polar bonds and is very soluble in water, but CO2 is nonpolar and is poorly soluble in water. Copyright Macmillan Learning. Powered by Cognero.

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Chap 02_8e 57. Of the seven the steps listed, which four (in the correct order) are needed to prepare 1 L of a 0.02 M Tris buffer solution at pH 7.6? A lab station has a 0.1 M solution of Tris in its protonated form, 0.1 M solution of HCl and NaOH, and plentiful distilled water. The Ka of Tris is 8.32 × 10–9. 1. Calculate the volume of 0.1 M Tris to use (C1V1 = C2V2). 2. Calculate the volume of 0.1 M HCl to use (C1V1 = C2V2). 3. Calculate the volume of 0.1 M NaOH to use (C1V1 = C2V2). 4. Use the Henderson-Hasselbalch equation to calculate the ratio of Tris base to protonated Tris. 5. Adjust the pH to 7.6 by adding 0.1 M NaOH. 6. Adjust the pH to 7.6 by adding 0.1 M HCl. 7. Fill to 1 L with distilled water. a. 1, 4, 6, 7 b. 1, 4, 5, 7 c. 1, 2, 4, 7 d. 1, 3, 4, 7 e. 1, 7, 4, 6 58. In water, which substance would most force surrounding water molecules to become highly ordered? a. CH2O b. CH4 c. NH3 d. CH3CH2OH e. None of the answers is correct.

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Chap 02_8e 59. According to the titration curve shown, what is the approximate pKa of acid A?

a. 0.2 b. 0.5 c. 3.2 d. 3.8 e. 4.8 60. Which factor causes water to have a bent geometry rather than a linear geometry? a. the net dipole of a water molecule b. the unshared electron pairs (nonbonding orbitals) on the oxygen atom c. the electronegativity difference between hydrogen and oxygen d. the unequal electron sharing between hydrogen and oxygen e. All of the answers are correct. 61. Consider an acetate buffer, initially at the same pH as its pKa (4.76). When sodium hydroxide (NaOH) is mixed with this buffer, the: a. pH remains constant. b. pH rises more than if the same amount of NaOH is added to an acetate buffer initially at pH 6.76. c. pH rises more than if the same amount of NaOH is added to unbuffered water at pH 4.76. d. ratio of acetic acid to acetate ion in the buffer decreases. e. sodium acetate formed precipitates because it is less soluble than acetic acid. Copyright Macmillan Learning. Powered by Cognero.

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Chap 02_8e 62. The Henderson-Hasselbalch equation: a. allows the graphic determination of the molecular weight of a weak acid from its pH alone. b. does not explain the behavior of di- or tribasic weak acids. c. employs the same value for pKa for all weak acids. d. is equally useful with solutions of acetic acid and of hydrochloric acid. e. relates the pH of a solution to the pKa and the concentrations of acid and conjugate base. 63. Draw a titration curve for a monoprotic weak acid and indicate the region in which the buffering capacity of the system is greatest.

64. If ice were denser than water, how would that affect life on Earth?

65. In proteins, the amino acid histidine (His) plays an important role in many biological reactions. The pKa for the protonation of His to form HisH+ = 6.0. When pH = 7.0, what is the fraction of total histidine that will be in the HisH+ form?

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Chap 02_8e 66. Phosphoric acid (H3PO4) has three dissociable protons with the pKa values shown. Which form of phosphoric acid predominates in a solution at pH 4? Explain. Acid pKa H3PO4 2.14 H2PO4–

6.86

HPO42–

12.4

67. Define pKa for a weak acid in two ways: (1) in relation to its acid dissociation constant, Ka, and (2) by reference to a titration curve for the weak acid.

68. For a weak acid with a pKa of 6.0, show how to calculate the ratio of acid to base at pH 5.

69. Explain with an appropriate diagram why amphipathic molecules tend to form micelles in water. What force drives micelle formation?

70. A weak acid HA, has a pKa of 5.0. If 1.0 mol of this acid and 0.1 mol of NaOH were dissolved in one liter of water, what is the final pH?

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Chap 02_8e 71. (a) In terms of osmolarity, briefly define isotonic, hypotonic, and hypertonic solutions. (b) Describe what happens when a cell is placed in each of these types of solutions.

72. Recall the equilibria: H+ + HCO3– ⇋ H2CO3 ⇋ CO2 + H2O Severe diarrhea is accompanied by a loss of HCO3– . If untreated, will the condition result in acidosis or alkalosis? Use the bicarbonate buffer system given in the scheme above and Le Chatelier's principle to explain your answer.

73. Name and briefly define five types of noncovalent interactions that occur between biological molecules.

74. What is the pH of a solution containing 0.2 M acetic acid (pKa = 4.7) and 0.1 M sodium acetate?

75. Explain the fact that ethanol (CH3CH2OH) is more soluble in water than is ethane (CH3CH3).

76. A solution is made by combining 50 mL of a 0.1 M sodium acetate solution with 150 mL of 1 M acetic acid (pKa = 4.7). What is the pH of the resulting solution?

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Chap 02_8e 77. After adding 100 mL of a solution containing 0.5 mol of acetic acid per liter to 400 mL of 0.5 M NaOH, what is the final pH? (The pKa of acetic acid is 4.7.)

78. Speculate why weak forces, not strong forces, are the basis for molecular recognition among biomolecules.

79. For each pair, circle the conjugate base. RCOOH RCOO– RNH2

RNH3+

H2PO4–

H3PO4

H2CO3

HCO3–

80. Explain the fact that triethylammonium chloride ((CH3CH2)3N-HCl) is more soluble in water than is triethylamine ((CH3CH2)3N).

81. As two atoms get nearer to each other, do van der Waals attractive forces always increase?

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Chap 02_8e Answer Key 1. e 2. a 3. c 4. b 5. a 6. d 7. d 8. e 9. e 10. a 11. b 12. b 13. c 14. a 15. b 16. a 17. a 18. b 19. c 20. d 21. e 22. b 23. b 24. a 25. e 26. d Copyright Macmillan Learning. Powered by Cognero.

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Chap 02_8e 27. d 28. e 29. e 30. d 31. c 32. c 33. a 34. a 35. e 36. b 37. b 38. c 39. d 40. b 41. d 42. d 43. a 44. a 45. d 46. a 47. a 48. d 49. e 50. a 51. e 52. d 53. c 54. b Copyright Macmillan Learning. Powered by Cognero.

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Chap 02_8e 55. d 56. c 57. b 58. b 59. d 60. b 61. d 62. e 63. The inflection point, which occurs when the weak acid has been exactly one-half titrated with NaOH, occurs at a pH equal to the pKa of the weak acid. The region of greatest buffering capacity (where the titration curve is flattest) occurs at pH values of pKa ± 1 (see Fig. 2-17). 64. Ice that formed at the surface of bodies of water would sink; hence, streams, ponds, lakes, and so on would freeze from the bottom up. With a reservoir of ice at the bottom, they would be perpetually cold, and in the limit they would freeze solid, precluding life as we know it. 65. Use the Henderson-Hasselbalch equation to determine the ratio of [His] to [HisH+]. pH = pKa + log ([His]/[HisH+]) 7.0 = 6.0 + log ([His]/[HisH+]) 1.0 = log ([His]/[HisH+]) [His]/[HisH+] = antilog (1) = 10 To determine the fraction of the total in the HisH+ form, [His]total = [His] + [HisH+], fraction = [HisH+]/[His]total = [HisH+]/([His] + [HisH+]) substitute from ratio calculated above = [HisH+]/(10[HisH+] + [HisH+]) = 1/11, or 0.09 66. At pH 4, the first dissociable proton (pKa = 2.14) has been titrated nearly completely, and the second (pKa = 6.86) has just started to be titrated. The dominant form at pH 4 is therefore H2PO4– , the form with one dissociated proton (see Fig. 2-15). 67. (1) pKa = –log Ka. (2) See Fig. 2-17; pKa is the value of pH at the inflection point in a plot of pH versus extent of titration of the weak acid. At the pKa, the concentration of ionized acid equals the concentration of nonionized acid. Copyright Macmillan Learning. Powered by Cognero.

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Chap 02_8e

68.

69. Micelle formation minimizes the surface area of the hydrophobic part of amphipathic molecules that contacts the polar solvent, water. Hydrophobic interactions between hydrophobic moieties are the driving force for micelle formation. When amphipathic molecules form micelles in water, the entropy decrease, due to the formation of ordered arrays of water molecules around the hydrophobic moieties, is minimized (see Fig. 2-7). 70. Combining 1 mol of weak acid with 0.1 mol of NaOH yields 0.9 mol of weak acid and 0.1 mol of salt.

71. (a) An isotonic solution has the same osmolarity as the solution to which it is being compared. A hypotonic solution has a lower osmolarity than the solution to which it is being compared. A hypertonic solution has a higher osmolarity than the solution to which it is being compared. (b) Higher osmolarity results in osmotic pressure, which generally leads to movement of water across a membrane. In an isotonic solution, in which the osmolarity of the solution is the same as the cell cytoplasm, there will be no net water movement. In a hypotonic solution, water will move into the cell causing the cell to swell and possibly burst. In a hypertonic solution, water will move out of the cell and it will shrink. 72. Acidosis. The removal of HCO3– will pull the equilibria in the direction of HCO3– , which will produce H+, thereby lowering the pH. 73. (1) Hydrogen bonds: weak electrostatic attractions between one electronegative atom (such as oxygen or nitrogen) and a hydrogen atom covalently linked to a second electronegative atom; (2) electrostatic interactions: relatively weak charge-charge interactions (attractions of opposite charges, repulsions of like charges) between two ionized groups; (3) hydrophobic interactions: the forces that tend to bring two hydrophobic groups together, reducing the total area of the two groups that is exposed to surrounding molecules of the polar solvent (water); (4) van der Waals interactions: weak interactions between the electric dipoles that two close-spaced atoms induce in each other; (5) tightly bound water molecules can form as an essential part of the binding site in a protein for its ligand. 74.

75. Ethanol can form hydrogen bonds with water molecules, but ethane cannot. When ethanol dissolves, there is some decrease in the system's entropy from formation of clathrate around the alkyl portion, but this is more than compensated for by the favorable interactions (hydrogen bonds) of the hydroxyl group of ethanol with water molecules. Ethane cannot form such hydrogen bonds and is therefore insoluble in water.

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Chap 02_8e 76.

77. Addition of 200 mM of NaOH (400 mL×0.5 M) to 50 mM of acetic acid (100 mL×0.5 mM) completely titrates the acid so that it can no longer act as a buffer and leaves 150 mM of NaOH dissolved in 500 mL, an [OH– ] of 0.3 M. Given [OH– ], [H+] can be calculated from the equilibrium constant for the dissociation of water (the ion product of water): [H+][OH– ] = 10–14 [H+] = 10–14 M2/0.3 M pH is, by definition, log (1/[H+]) pH = log (0.3 M/10–14 M2) = 12.48 78. Weak forces make the biological interactions reversible within physiological constraints. The cumulative effects of many weak interactions can be very significant. Strong forces would require large amounts of energy to reverse any interaction. 79. RCOO– , RNH2, H2PO4– , HCO3– 80. Triethylammonium chloride is an ionic substance. The positive charge of the triethylammonium ion makes it hydrophilic. This leads to stronger favorable interactions with water, leading to increased solubility. Triethylamine is uncharged. 81. No, the attractive forces created by the transient dipole-induced dipole interaction increases until the van der Waals radius is reached, where the net attraction is maximal. At this point, the electron clouds begin to repel each other.

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Chap 03_8e Indicate the answer choice that best completes the statement or answers the question. 1. When the ribosome forms a peptide bond, which two atoms form a covalent bond? a. the α carbon and the amino nitrogen b. the amino nitrogen and carboxylic acid carbon c. the α carbon and the carboxylic acid carbon d. the amino nitrogen and the β carbon e. It depends on the amino acids being joined. 2. How are sequential reactions controlled in the Edman degradation procedure? a. A high salt step is followed by a low salt step. b. A low salt step is followed by a high salt step. c. A high pH step is followed by a low pH step. d. A low pH step is followed by a high pH step. e. None of the answers is correct. 3. Which of the lanes in the gel would represent an "uninduced" sample?

a. 1 b. 2 c. 3 d. 4 e. 5

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Chap 03_8e 4. Selective precipitation of a protein from a crude extract is MOST effective by which molecule? a. ammonium sulfate b. urea c. sodium dodecyl sulfate d. EDTA (ethylenediaminetetraacetic acid) e. All of the answers are correct. 5. By convention, polypeptides are read in which order? a. N to C terminus b. C to N terminus c. 5′ to 3′ d. 3′ to 5′ e. smallest to largest amino acid by molecular weight 6. In an SDS-PAGE experiment two markers of molecular weight, 11,000 g/mol and 3,000 g/mol, traveled 5 cm and 9 cm, respectively. Approximately, how far will a fragment of size 7,945 g/mol travel? a. 6 cm b. 5 cm c. 8 cm d. 7 cm e. The answer cannot be determined from the information given. 7. In a conjugated protein, a prosthetic group is: a. a fibrous region of a globular protein. b. a nonidentical subunit of a protein with many identical subunits. c. a part of the protein that is not composed of amino acids. d. a subunit of an oligomeric protein. e. synonymous with "protomer." 8. Which reagent and application are mismatched? a. dithiothreitol, reduction of disulfide bonds b. dansyl chloride, modify the C-terminal amino acid c. iodoacetate, carboxymethylation to prevent disulfide formation d. anhydrous trifluoroacetic acid, removal of N-terminal amino acid e. Fmoc, protecting group

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Chap 03_8e 9. Which statement is true about the pKa values for ionizable R groups of amino acids within a polypeptide? a. The pKa values for R groups do not change from free amino acids. b. The pKa values for R groups are 1 pH unit higher than free amino acids. c. The pKa values for R groups are 1 pH unit lower than free amino acids. d. The pKa values for R groups vary depending on the local environment of the side chain. e. The pKa values for R groups depend on how close the R group is to the N or C terminus of the polypeptide. 10. Two amino acids of the standard 20 contain sulfur atoms. They are: a. cysteine and serine. b. cysteine and threonine. c. methionine and cysteine. d. methionine and serine. e. threonine and serine. 11. The chirality of an amino acid results from the fact that its α carbon: a. has no net charge. b. is a carboxylic acid. c. is bonded to four different chemical groups. d. is in the L absolute configuration in naturally occurring proteins. e. is symmetric. 12. The functional differences, as well as differences in three-dimensional structures, between two different enzymes from E. coli result directly from their different: a. affinities for ATP. b. amino acid sequences. c. roles in DNA metabolism. d. roles in the metabolism of E. coli. e. secondary structures. 13. Identify the pair of peptides that are NOT distinguished by tandem mass spectrometry. a. VTSPLYANEGK and VTCPLYANEGK b. VTSPLYANEGK and VTSPLYADEGK c. VTSPLYANEGK and VTSPIYANEGK d. VTSPLYANEGK and VSTPLYANEGK e. All of the answer choices are correct.

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Chap 03_8e 14. According to the diagram, what is the average net charge of this amino acid at pH = 2?

a. +1 b. +0.5 c. 0 d. –0.5 e. –1 15. The pKa of lysine's carboxyl group, amino group, and side chain are 2.2, 9.0, and 10.5, respectively. If lysine is in a pH 13 solution, what is its net charge? a. –2 b. –1 c. 0 d. +1 e. +2

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Chap 03_8e 16. Which statement is correct with respect to the amino acid composition of proteins? a. Larger proteins have a more uniform distribution of amino acids than smaller proteins. b. Proteins contain at least one each of the 20 different standard amino acids. c. Proteins with different functions usually differ significantly in their amino acid composition. d. Proteins with the same molecular weight have the same amino acid composition. e. The average molecular weight of an amino acid in a protein increases with the size of the protein. 17. The "signature sequence" shown represents a portion of a protein from four different organisms. The proteins can be classified as:

a. homologs. b. orthologs. c. paralogs. d. both homologs and orthologs. e. both homologs and paralogs. 18. In a highly basic solution, pH = 13, which is the dominant form of glycine? a. NH2—CH2—COOH b. NH2—CH2—COO– c. NH2—CH3+—COO– d. NH3+—CH2—COOH e. NH3+—CH2—COO– 19. At pH 7.0, converting a proline to hydroxyproline, will have what effect on the overall charge of the protein containing it? a. It will become more negative. b. It will become more positive. c. It will stay the same. d. There is not enough information to answer the question. e. The answer depends on the salt concentration.

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Chap 03_8e 20. At pH 7.0, converting a glutamic acid to γ-carboxyglutamate, will have what effect on the overall charge of the protein containing it? a. It will become more negative. b. It will become more positive. c. It will stay the same. d. There is not enough information to answer the question. e. The answer depends on the salt concentration. 21. The amino acid proline is unique because the R group: a. has a phosphate attached. b. is cyclical. c. is attached to the carboxylic acid carbon. d. is positively charged. e. None of the answers is correct. 22. R. Bruce Merrifield provided an innovation to synthesize peptides. Which statement does NOT describe part of his technology? a. One end of the peptide is attached to a solid support. b. At each step in the cycle, protective chemical groups block unwanted reactions. c. The peptide product must be purified between each step of the cycle. d. The support for the peptides is similar to a chromatography column. e. All of the statements describe part of Merrifield's technology. 23. The term "specific activity" differs from the term "activity" in that specific activity: a. is measured only under optimal conditions. b. is the activity (enzyme units) in a milligram of protein. c. is the activity (enzyme units) of a specific protein. d. refers only to a purified protein. e. refers to proteins other than enzymes. 24. In a mixture of the five proteins listed, which should elute second in size-exclusion (gel-filtration) chromatography? a. cytochrome c, Mr = 13,000 b. immunoglobulin G, Mr = 145,000 c. ribonuclease A, Mr = 13,700 d. RNA polymerase, Mr = 450,000 e. serum albumin, Mr = 68,500

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Chap 03_8e 25. The first step in two-dimensional gel electrophoresis generates a series of protein bands by isoelectric focusing. In a second step, a strip of this gel is turned 90 degrees, placed on another gel containing SDS, and electric current is again applied. In this second step: a. proteins with similar isoelectric points become further separated according to their molecular weights. b. the individual bands become stained so that the isoelectric focus pattern can be visualized. c. the individual bands become visualized by interacting with protein-specific antibodies in the second gel. d. the individual bands undergo a second, more intense isoelectric focusing. e. the proteins in the bands separate more completely because the second electric current is in the opposite polarity to the first current. 26. Which type of structure describes the overall three-dimensional folding of a polypeptide? a. primary structure b. secondary structure c. tertiary structure d. quaternary structure e. None of the answers is correct. 27. Why can only some amino acids be used to measure protein concentration based on absorption of UV light? a. Only some amino acids are aromatic. b. Only some amino acids are positively charged. c. Only some amino acids are strongly hydrophobic. d. Only some amino acids are strongly hydrophilic. e. Only some amino acids are negatively charged. 28. The peptide alanylglutamylglycylalanylleucine has: a. a disulfide bridge. b. five peptide bonds. c. four peptide bonds. d. no free carboxyl group. e. two free amino groups.

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Chap 03_8e 29. A nonapeptide was determined to have the amino acid composition (Lys)2, (Gly)2, (Phe)2, His, Leu, Met. The native peptide was incubated with 1-fluoro-2,4-dinitrobenzene (FDNB) and then hydrolyzed; 2,4dinitrophenylhistidine was identified by HPLC. When the native peptide was exposed to cyanogen bromide (CNBr), an octapeptide and free glycine were recovered. Incubation of the native peptide with trypsin gave a pentapeptide, a tripeptide, and free Lys. 2,4-Dinitrophenyl-histidine was recovered from the pentapeptide, and 2,4-dinitrophenylphenylalanine was recovered from the tripeptide. Digestion with the enzyme pepsin produced a dipeptide, a tripeptide, and a tetrapeptide. The tetrapeptide was composed of (Lys)2, Phe, and Gly. What is the native sequence determined to be? a. Gly–Phe–Lys–Lys–Gly–Leu–Met–Phe–His b. His–Leu–Gly–Lys–Lys–Phe–Phe–Gly–Met c. His–Leu–Phe–Gly–Lys–Lys–Phe–Met–Gly d. His–Phe–Leu–Gly–Lys–Lys–Phe–Met–Gly e. Met–Leu–Phe–Lys–Phe–Gly–Gly–Lys–His 30. The uncommon amino acid selenocysteine has an R group with the structure —CH2—SeH (pKa ≈ 5). In an aqueous solution, pH = 7.0, the R group of selenocysteine would be: a. deprotonated. b. uncharged. c. protonated. d. dimerized. e. aromatic. 31. The structure is a molecule used in the sweeteners Equal and NutraSweet. When heated, the peptide bond will hydrolyze into methanol and which two amino acids?

a. asparagine and tyrosine b. aspartic acid and phenylalanine c. glutamic acid and phenylalanine d. aspartic acid and tryptophan e. glutamic acid and histidine

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Chap 03_8e 32. An octapeptide composed of four repeating glycylalanyl units has: a. one free amino group on an alanyl residue. b. one free amino group on an alanyl residue and one free carboxyl group on a glycyl residue. c. one free amino group on a glycyl residue and one free carboxyl group on an alanyl residue. d. two free amino and two free carboxyl groups. e. two free carboxyl groups, both on glycyl residues. 33. Which two amino acids differ from each other by only one atom? a. Ser and Thr b. Leu and Ile c. Ala and Ser d. Asp and Asn e. Ser and Cys 34. According to the table, ion-exchange chromatography would be the LEAST effective method to separate which protein mixture? Protein Molecular weight pI A 12,500 3.2 B 13,200 5.7 C 13,500 10.5 D 36,900 5.8 E 78,400 6.1 a. proteins A, B, and C b. proteins A, C, and D c. proteins B, D, and E d. proteins B, C, and D e. All of the answers are correct.

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Chap 03_8e 35. Compare the sequences taken from four different proteins, and select the answer that BEST characterizes their relationships. A

1 DVEKGKKIDIMKCS

HTVEKGGKHKTGPNLH

GLFGRKTGQAPGYSYT

2 DVQRALKIDNNLGQ

HTVEKGAKHKTAPNVH

GLADRIAYQAKATNEE

3 LVTRPLYIFPNEGQ

HTLEKAAKHKTGPNLH

ALKSSKDLMFTVINDD

4 FFMNEDALVARSSN

HQFAASSIHKNAPQFH

NLKDSKTYLKPVISET

a. Based only on sequences in column B, protein 4 reveals the greatest evolutionary divergence. b. Comparing proteins 1 and 2 in column A reveals that these two proteins have diverged the most throughout evolution. c. Protein 4 is the protein that shows the greatest overall homology to protein 1. d. Proteins 2 and 3 show a greater evolutionary distance than proteins 1 and 4. e. The portions of amino acid sequence shown suggest that these proteins are completely unrelated.

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Chap 03_8e 36. According to the diagram, what is the average net charge of this amino acid at pH = 1?

a. +1 b. +0.5 c. 0 d. –0.5 e. –1 37. All of the 20 common amino acids contain an R group that is attached to the: a. carboxyl group. b. amino group. c. α carbon. d. β carbon. e. It depends on the amino acid.

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Chap 03_8e 38. For the study of a protein in detail, an effort is usually made to first: a. conjugate the protein to a known molecule. b. determine its amino acid composition. c. determine its amino acid sequence. d. determine its molecular weight. e. purify the protein. 39. According to the diagram, which is the BEST estimate of this amino acid's isoelectric point?

a. 0.5 b. 1 c. 1.5 d. 6 e. 11

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Chap 03_8e 40. Which type of structure refers to particularly stable arrangements of amino acid residues in a protein that give rise to recurring patterns? a. primary structure b. secondary structure c. tertiary structure d. quaternary structure e. None of the answers is correct. 41. All of the amino acids that are found in proteins, except for proline, contain a(n) _____ group. a. amino b. carbonyl c. carboxyl d. ester e. thiol 42. One method used to prevent disulfide bond interference with protein sequencing procedures is: a. cleaving proteins with proteases that specifically recognize disulfide bonds. b. protecting the disulfide bridge against spontaneous reduction to cysteinyl sulfhydryl groups. c. reducing disulfide bridges and preventing their re-formation by further modifying the —SH groups. d. removing cystines from protein sequences by proteolytic cleavage. e. sequencing proteins that do not contain cysteinyl residues. 43. A major advance in the application of mass spectrometry to macromolecules came with the development of techniques to overcome which problem? a. Macromolecules were insoluble in the solvents used in mass spectrometry. b. Mass spectrometric analyses of macromolecules were too complex to interpret. c. Mass spectrometric analysis involved molecules in the gas phase. d. Most macromolecules could not be purified to the degree required for mass spectrometric analysis. e. The specialized instruments required were prohibitively expensive. 44. For amino acids with neutral R groups, at any pH below the pI of the amino acid, the population of amino acids in solution will have: a. a net negative charge. b. a net positive charge. c. no charged groups. d. no net charge. e. positive and negative charges in equal concentration.

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Chap 03_8e 45. What is the approximate charge difference between glutamic acid and α-ketoglutarate at pH 9.5? a. 0 b. c. 1 d. 1 e. 2 46. Iodoacetamides, maleimides, benzyl halides, and bromomethyl ketones can all be used to modify the _____ group on _____ residues. a. amino; basic b. phenyl; Tyr and Trp c. carboxyl; acidic d. sulfhydryl; Cys e. hydroxyl; Ser and Tyr 47. The average molecular weight of the 20 standard amino acids is 138, but biochemists use 110 when estimating the number of amino acids in a protein of known molecular weight. Why? a. The number 110 is based on the fact that the average molecular weight of a protein is 110,000 with an average of 1,000 amino acids. b. The number 110 reflects the higher proportion of small amino acids in proteins, as well as the loss of water when the peptide bond forms. c. The number 110 reflects the number of amino acids found in the typical small protein, and only small proteins have their molecular weight estimated this way. d. The number 110 takes into account the relatively small size of nonstandard amino acids. e. The number 138 represents the molecular weight of conjugated amino acids. 48. Amino acids are ampholytes because they can function as either a(n): a. acid or a base. b. neutral molecule or an ion. c. polar or a nonpolar molecule. d. standard or a nonstandard monomer in proteins. e. transparent or a light-absorbing compound.

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Chap 03_8e 49. To determine the isoelectric point of a protein, first establish that a gel: a. contains a denaturing detergent that can distribute uniform negative charges over the protein's surface. b. exhibits a stable pH gradient when ampholytes become distributed in an electric field. c. is washed with an antibody specific to the protein of interest. d. neutralizes all ionic groups on a protein by titrating them with strong bases. e. relates the unknown protein to a series of protein markers with known molecular weights, Mr. 50. According to the diagram, which pH range offers the greatest buffering power for this amino acid?

a. 0.5–1.5 b. 0–1 c. 1–2 d. 2–3 e. 1–3

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Chap 03_8e 51. According to the diagram, how many titratable groups does this amino acid have?

a. 0 b. 1 c. 2 d. 3 e. It cannot be determined by this diagram. 52. The MOST useful way to classify amino acids is by: a. molecular weight. b. pKa. c. polarity. d. propensity in proteins. e. alphabetical order.

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Chap 03_8e 53. A protein with a high percentage of lysine and arginine residues would be BEST purified and concentrated with which type of column? a. cation exchange b. anion exchange c. size-exclusion chromatography d. affinity chromatography e. reverse-phase chromatography 54. Which pair of amino acids can be used to measure the concentration of proteins based on absorption of UV light? a. proline and valine b. serine and threonine c. aspartate and glutamate d. lysine and histidine e. tyrosine and tryptophan 55. The pKa's of arginine's a-carboxyl group, a-amino group, and side chain are 1.8, 9.0, and 12.5, respectively. What is arginine's pI? a. 7.8 b. 7.2 c. 10.8 d. 5.4 e. 12.5 56. Which correctly matches the amino acid name with its one-letter abbreviation? a. tyrosine, T b. lysine, L c. phenylalanine, P d. aspartic acid, D e. proline, R 57. Which compound is a side product of a peptide bond formation? a. water b. phosphate c. ammonium d. carboxylic acid e. None of the answers is correct.

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Chap 03_8e 58. According to the table, size-exclusion (gel-filtration) chromatography could NOT be used to separate which protein mixture? Protein Molecular weight pI A 12,500 3.2 B 13,200 5.7 C 13,500 10.5 D 36,900 5.8 E 78,400 6.1 a. proteins A, D, and F b. proteins C, E, and F c. proteins B, E, and F d. proteins A, B, and C e. All of the answers are correct. 59. Prosthetic groups in the class of proteins known as glycoproteins are composed of: a. carbohydrates. b. flavin nucleotides. c. lipids. d. metals. e. phosphates. 60. Which item is NOT a biochemical use or function of peptides of small molecular weight? a. artificial sweetener b. hormone c. poison d. antibiotics e. All of the answer choices are correct. 61. A protein with a high percentage of aspartate and glutamate residues would be BEST purified and concentrated with which type of column? a. cation exchange b. anion exchange c. size-exclusion chromatography d. affinity chromatography e. reverse-phase chromatography

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Chap 03_8e 62. The protein bovine serum albumin (BSA), has a molecular weight of about 66,400. Using the Lambert-Beer Law, calculate the concentration of a sample of BSA with an absorbance of 1.3 at 280 nm, assuming the molar extinction coefficient at 280 nm is 43,824 M–1 cm–1. a. 0.51 mg/mL b. 0.86 mg/mL c. 1.97 mg/mL d. 2.56 mg/mL e. 3.78 mg/mL 63. Which statement about aromatic amino acids is correct? a. All are strongly hydrophilic. b. Histidine's ring structure results in its being categorized as aromatic or basic, depending on pH. c. On a molar basis, tryptophan absorbs more ultraviolet light than tyrosine. d. The major contribution to the characteristic absorption of light at 280 nm by proteins is the phenylalanine R group. e. The presence of a ring structure in its R group determines whether or not an amino acid is aromatic.

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Chap 03_8e 64. The gel illustrates the purification of the RecA protein from E. coli. This gel was loaded from the top. Which statement BEST describes how proteins "run" in an SDS gel?

a. The proteins are separated primarily by molecular weight—the largest molecular weight proteins are on the bottom, and the smallest are on the top. b. The proteins are separated primarily by molecular weight—the smallest molecular weight proteins are on the bottom, and the largest are on the top. c. The proteins are separated primarily by charge—the protein with the smallest pI is on the top, and the protein with the largest pI is on the bottom. d. The proteins are separated primarily by charge—the protein with the largest pI is on the top, and the protein with the smallest pI is on the bottom. e. The proteins are separated primarily by their propensity to precipitate—as electrophoresis progresses, the heat generated by the current denatures proteins faster or slower. The slowest to denature is on the bottom, and the fastest to denature is on the top. 65. The term "proteome" has been used to describe: a. regions (domains) within proteins. b. regularities in protein structures. c. the complement of proteins expressed by an organism's genome. d. the structure of a protein-synthesizing ribosome. e. the tertiary structure of a protein.

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