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Chapter 01: Biochemistry Concepts and Themes 1. 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 ANSWER: e 2. In a bacterial cell, the DNA is in the: a. cell envelope. b. cell membrane. c. nucleoid. d. nucleus. e. ribosomes. ANSWER: c 3. In eukaryotes, the nucleus is enclosed by a double membrane called the: a. cell membrane. b. nuclear membrane. c. nucleolus. d. nucleoplasm. e. nucleosome. ANSWER: b 4. Which is the range of typical diameters of animal and plant cells? a. 0.1 μm to 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 ANSWER: c 5. 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. ANSWER: b 6. Which is a list of organelles? Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes a. mitochondria, chromatin, endoplasmic reticulum b. peroxisomes, lysosomes, plasma membrane c. proteasomes, chromatin, lysosomes d. mitochondria, endoplasmic reticulum, peroxisomes e. All of the answers are correct. ANSWER: d 7. 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 ANSWER: b 8. Which element is NOT among the four most abundant in living organisms? a. carbon b. hydrogen c. nitrogen d. oxygen e. phosphorus ANSWER: e 9. 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 ANSWER: b 10. 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 Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes e. hydroxyl and ketone ANSWER: b 11. 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. ANSWER: a 12. 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. ANSWER: d 13. The breakage of a phosphoanhydride bond in ____________ 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 ANSWER: c 14. 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. ANSWER: a 15. Hereditary information (with the exception of some viruses) is preserved in: a. deoxyribonucleic acid. b. membrane structures. c. nuclei. Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes d. polysaccharides. e. ribonucleic acid. ANSWER: a 16. The three-dimensional structure of a protein is determined primarily by: a. electrostatic guidance from nucleic acid structure. b. noncovalent association with other proteins. 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. ANSWER: e 17. 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. ANSWER: d 18. 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. ANSWER: c 19. Which does NOT contain a double membrane? a. mitochondrion b. ribosome c. chloroplast d. endoplasmic reticulum e. Golgi body ANSWER: b 20. Which is NOT found in both animal and plant cells? a. ribosome b. Golgi complex c. endoplasmic reticulum d. vacuole Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes e. mitochondrion ANSWER: d 21. 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 ANSWER: b 22. 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 ANSWER: c 23. 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 ANSWER: a Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes 24. 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 ANSWER: e 25. 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. ANSWER: c 26. 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 ANSWER: c 27. 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. ANSWER: a 28. 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. Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes ANSWER: e 29. 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 ANSWER: a 30. 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 ANSWER: a 31. 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. ANSWER: a 32. All cells are surrounded by a plasma membrane composed of lipid and protein molecules. What is the function of the plasma membrane? ANSWER: 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. 33. Most cells of higher plants have a cell wall outside the plasma membrane. What is the function of the cell wall? ANSWER: The cell wall provides a rigid, protective shell for the cell. It is porous, allowing water and small molecules to pass readily. It is also rigid enough to resist the swelling of the cell caused by the accumulation of water (see Fig. 1-4). 34. What is the difference, if any, between cytosol and cytoplasm? Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes ANSWER: The cytoplasm is the internal volume enclosed by the plasma membrane; the cytosol is the aqueous portion of the cytoplasm. 35. Draw the structures of the functional groups in their nonionized forms for (a) hydroxyl, (b) carboxyl, (c) amino, (d) phosphoryl in their nonionized forms. ANSWER:
36. 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? ANSWER: 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. 37. Name two functions of (a) proteins, (b) nucleic acids, (c) polysaccharides, (d) lipids. ANSWER: 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. 38. 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? ANSWER: 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. 39. Describe the relationship between a living organism and its surroundings in terms of both matter and energy. ANSWER: 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. 40. 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? Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes ANSWER: The endergonic (thermodynamically unfavorable) reaction is coupled to an exergonic (thermodynamically favorable) reaction through a shared intermediate, so that the overall freeenergy change of the coupled reactions is negative (the overall reaction is exergonic). 41. 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. ANSWER: 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. 42. (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.
ANSWER: (a) and (c) see Fig. 1.15 (b) exergonic reaction 43. Briefly, compare and contrast the three domains of life. ANSWER: 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. Eukaryotes also contain multiple, membraneenclosed sub-compartments called organelles. 44. (a) What is the diagram? (b) Describe what it illustrates about the relationship between animals, halophiles, slime molds, and gram-positive bacteria. (c) Explain the evidence used in construction of this diagram.
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Chapter 01: Biochemistry Concepts and Themes
ANSWER: (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 gram-positive 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. 45. Why is the use of the expression ‘Mr = 18,000 daltons’ incorrect? ANSWER: Mr is a ratio and therefore dimensionless. Daltons are only used when describing molecular mass, not molecular weight or relative molecular mass. 46. An idea or experiment is within the realm of science if it adheres to which key elements? ANSWER: An idea or experiment is within the realm of science if it focuses on the natural universe, is carried out within a scientific context, and if it has reproducible results that are reported honestly. 47. What is a hypothesis? ANSWER: A hypothesis is a proposal that provides a reasonable explanation for observations. It is not yet substantiated by sufficient experimental tests. 48. Scientific endeavors can be understood by applying a systematic process of inquiry called: a. an assumption of objectivity. b. a hypothesis. c. a postulate of objectivity. d. the scientific method. Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes e. a scientific theory. ANSWER: d 49. Scientific hypotheses and theories are often presented in peer-reviewed scientific literature. According to the Publishers Association of the United Kingdom, there are more than _____ peer-reviewed scientific journals worldwide. a. 200 b. 1,900 c. 10,000 d. 16,000 e. 1.4 million ANSWER: d 50. The practice of science as we know it is about _______ years old. a. 200 b. 1,900 c. 10,000 d. 16,000 e. 1.4 million ANSWER: a 51. Science advances in a variety of ways; not just by the implementation of the scientific method. Discuss two other productive pathways towards scientific advancement. ANSWER: There are 4 alternative approaches to scientific knowledge in Table 1.1 of the text. If the student discusses the ‘Hypothesis→experiment→answer’ approach, this answer is incorrect; this is the classical scientific method. The 4 correct approaches are: The Serendipity approach occurs when an experiment designed to distinguish between outcome X and outcome Y, results in unexpected outcome Z. The Inspiration approach occurs when simply moments of pondering about a hypothesis lend to the rise of new technologies and major advances. The Model-building and deduction approach can occur at a computer or a desk where modeling tools and technologies can reveal scientific knowledge; experiments are usually done to confirm the predictions of model-building. The Exploration and observation approach occurs when simply moments of observation, even without a hypothesis, lend to the attainment of new scientific knowledge. 52. A scientist is any person: a. who applies some version of the scientific method to solve a problem in the natural world. b. who makes an observation. c. who reproduces a scientific advancement. d. who works in a laboratory. e. with an advanced science degree. ANSWER: a 53. Which approach is considered the classic scientific method? Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes a. Exploration and observation b. Hypothesis → experiment → answer c. Inspiration d. Model-building and deduction e. Serendipity ANSWER: b 54. If a result suggests a particularly exciting idea, honesty demands that: a. the idea can be observed and measured. b. the idea can be tested. c. the next experiment conducted be the one most likely to disprove that idea. d. the result be reproduceable. e. the result can be produced in a vacuum. ANSWER: c 55. Scientific endeavors are grounded in the assumption that the forces and phenomena that make up the universe are unchanging. This is related to: a. honesty. b. observation. c. objectivity. d. reproducibility. e. serendipity. ANSWER: d 56. The MOST precise modern definition of a gene is a segment of genetic material that: a. codes for one polypeptide. b. codes for a final functional polypeptide or RNA product. c. determines one phenotype. d. determines one trait. e. codes for one protein. ANSWER: b 57. Functional DNA is NOT found in: a. bacterial nucleoids. b. chloroplasts. c. lysosomes. d. mitochondria. e. nuclei. ANSWER: c 58. Which list ranks the organisms in order of increasing number of genes? Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes a. S. cerevisiae, humans, nematodes b. S. cerevisiae, nematodes, humans c. nematodes, humans, S. cerevisiae d. nematodes, S. cerevisiae, humans e. humans, S. cerevisiae, nematodes ANSWER: b 59. What are the minimal components of a virus? a. DNA and a lipid membrane b. genome (DNA or RNA), a lipid membrane, and a viral coat c. genome (DNA or RNA) and a viral coat d. protein genome and a lipid membrane ANSWER: c 60. Which item is NOT electrophilic? a. proton b. sulfhydryl c. protonated imine d. carbonyl group e. phosphoryl group ANSWER: b 61. Which atom is a common electrophile? a. hydrogen atom b. oxygen atom of a carbonyl group c. oxygen atom of a phosphate group d. oxygen atom of a hydroxide group e. phosphorus of a phosphate group ANSWER: e 62. Which atom is a possible nucleophile? a. oxygen atom in a hydroxide ion b. oxygen atom of a carboxylate group c. nitrogen atom of a deprotonated amine d. All of the answers are correct. e. None of the answers are correct. ANSWER: d 63. Why is carbon a main element used in living organisms? ANSWER: Carbon has a great capacity to make substances of widely different sizes, shapes, and composition. Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes 64. The reaction A + B → C has a ΔG'° of –20 kJ/mol at 25°C. Starting under standard conditions, one can predict that: a. at equilibrium, the concentration of B will exceed the concentration of A. b. at equilibrium, the concentration of C will be less than the concentration of A. c. at equilibrium, the concentration of C will be much greater than the concentration of A or B. d. C will rapidly break down to A + B. e. when A and B are mixed, the reaction will proceed rapidly toward formation of C. ANSWER: c 65. For the reaction A → B, the Keq' is 104. If a reaction mixture originally is 1 mM in A and contains no B, which statement must be true? a. At equilibrium, there will be far more B than A. b. The rate of the reaction is very slow. c. The reaction requires coupling to an exergonic reaction in order to proceed. d. The reaction will proceed toward B at a very high rate. e. ΔG'° for the reaction will be large and positive. ANSWER: a 66. For the reaction A → B, the Keq' is 10–6. If a reaction mixture originally is 1 mM in both A and B, which statement must be true? a. At equilibrium, there will still be equal levels of A and B. b. The rate of the reaction is very slow. c. At equilibrium, the amount of A will greatly exceed the amount of B. d. The reaction will proceed toward B at a very high rate. e. ΔG'° for the reaction will be large and negative. ANSWER: c 67. Which statement is true for the reaction A + B → C + D if its Keq for the reaction is 104? a. When the reaction has reached equilibrium, there will be significantly more A and B than C and D in the solution. b. The formation of A and B will proceed at a high rate. c. The value of ΔG'° will be large and positive. d. All of the statements are true. e. None of the statements are true. ANSWER: e 68. The products of scientific research are widely available in: a. international data banks. b. literature search engines. c. open-source programs. d. protein data banks. Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes e. All of the above are correct. ANSWER: e 69. Why is a laboratory notebook not a widely useful type of data bank? ANSWER: Widely useful data banks are online resources that curate and allow the interrogation of scientific information that has been acquired over many decades. Laboratory notebooks are typically used by scientists to track their daily methods and observations while conducting experiments. They are typically not widely available online in their raw form; but are instead used to write publicly available literature. Widely useful data banks include data banks that curate genomic sequence information, literature search engines, and the protein data bank. 70. Which is not a literature search engine? a. Google Scholar b. PubMed Central c. National Center for Biotechnology Information d. Web of Science e. None of the above ANSWER: c 71. What are Jmol and PyMOL? What can they be used for? ANSWER: Jmol and PyMOL are open-source programs available to anyone. They allow one to examine structural files and visualize structures of proteins and other macromolecules. 72. To find related DNA sequence of interest in several organisms, you can do a broad search using a program such as: a. BLAST. b. Jmol. c. PyMOL. d. NCBI. e. NMR. ANSWER: a 73. The Worldwide Protein Data Bank (PDB) has over __________ macromolecular structures. a. 50 b. 100 c. 2,000 d. 10,000 e. 200,000 ANSWER: e 74. Which data bank is a free depository of articles funded by the NIH and other U.S. government agencies? a. Google Scholar Copyright Macmillan Learning. Powered by Cognero.
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Chapter 01: Biochemistry Concepts and Themes b. PubMed Central c. National Center for Biotechnology Information d. Web of Science e. Worldwide Protein Data Bank ANSWER: b 75. Which data bank is a powerful subscription-based service accessible at academic and many commercial libraries by students, faculty, and employees? a. Google Scholar b. PubMed Central c. National Center for Biotechnology Information d. Web of Science e. Worldwide Protein Data Bank ANSWER: d 76. Which data bank curates protein and other macromolecular structures derived from x-ray crystallography, NMR, and cryo-electron microscopy? a. Google Scholar b. PubMed Central c. National Center for Biotechnology Information d. Web of Science e. Worldwide Protein Data Bank ANSWER: e 77. Which organization offers a wide range of resources, including the stored genomic sequence information from thousands of different organisms? a. Google Scholar b. PubMed Central c. National Center for Biotechnology Information d. Web of Science e. Worldwide Protein Data Bank ANSWER: c
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Chapter 02: Water: The Chemistry of Life 1. 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. ANSWER: d 2. 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 form hydrogen bonds d. the electronegativity of the oxygen in water e. All of the answers are correct. ANSWER: e 3. 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 ANSWER: a 4. Which image correctly represents hydrogen bonding?
a. A and D b. A and C c. B and C d. C and D e. B and D ANSWER: c Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life 5. 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. ANSWER: c 6. 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 occur when a hydrogen with a partial positive charge is positioned between two atoms with partial negative charges. ANSWER: d 7. 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. ANSWER: b 8. 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 Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life ANSWER: b 9. 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. ANSWER: a 10. 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 cage-like 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. ANSWER: d 11. 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. ANSWER: c 12. Which force plays the greatest role in stabilizing biological membranes? a. hydrogen bonding because it is 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 ANSWER: b 13. When two atoms are joined together covalently, the van der Waals radius of the atoms in the covalent bond Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life 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 ANSWER: a 14. Which diagram illustrates an amphipathic molecule?
a. A b. B c. C d. D e. E ANSWER: d 15. 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 ANSWER: d 16. If the pH of a solution is 5.5, what is the pOH? a. 8.5 b. –5.5 c. –8.5 d. 14 Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life e. 6.5 ANSWER: a 17. 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 ANSWER: b 18. 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 ANSWER: b 19. 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 ANSWER: d 20. 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 ANSWER: a 21. Which is the conjugate base of H2PO41–? a. H3PO4 b. H2PO42– Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life c. HPO42– d. HPO43– e. PO43– ANSWER: c 22. 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. ANSWER: a 23. According to the titration curve shown, what is the approximate pKa of acid A?
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Chapter 02: Water: The Chemistry of Life
a. 0.2 b. 0.5 c. 3.2 d. 3.8 e. 4.8 ANSWER: d 24. 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 ANSWER: b 25. 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?
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Chapter 02: Water: The Chemistry of Life
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. ANSWER: b 26. Which compound is a diprotic acid? a. CH3COOH b. NH4+ c. H2CO3 d. H3PO4 e. CH3CH2OH ANSWER: c 27. Polar molecules cannot easily pass through the cell membrane, but hydrophobic molecules can easily pass through the membrane. Both molecules shown below can raise blood pressure. Compare the molecules and select the statement that is true.
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Chapter 02: Water: The Chemistry of Life
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. ANSWER: a 28. 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 ANSWER: e 29. 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 Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life ANSWER: b 30. Name and briefly define four types of noncovalent interactions that occur between biological molecules. ANSWER: (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. 31. Explain the fact that ethanol (CH3CH2OH) is more soluble in water than is ethane (CH3CH3). ANSWER: Ethanol can form hydrogen bonds with water molecules, but ethane cannot. When ethanol dissolves, there is some decrease in the system's entropy due to the formation of clathrate around the alkyl group of ethanol. However, this decrease in entropy 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. 32. Explain the fact that triethylammonium chloride ((CH3CH2)3N-HCl) is more soluble in water than is triethylamine ((CH3CH2)3N). ANSWER: 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 and forms weaker interactions with water molecules. 33. Explain why amphipathic molecules tend to form micelles in water. What force drives micelle formation? ANSWER: 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 compensated by an overall increase in entropy due to the ordering of water molecules. 34. For each pair, choose the conjugate base. RCOOH RCOO– RNH2
RNH3+
H2PO4–
H3PO4
H2CO3 HCO3– ANSWER: RCOO–, RNH2, H2PO4–, HCO3– 35. Phosphoric acid (H3PO4) has three dissociable protons with the pKa values shown below. Which form of phosphoric acid predominates in a solution at pH 4? Explain. Acid pKa Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life H3PO4
2.14
H2PO4–
6.86
HPO42–
12.4
ANSWER: 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. 2.9 and 2.12). 36. 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. ANSWER: (1) pKa = –log Ka. (2) See Fig. 2.10; 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. 37. Describe a titration curve for a monoprotic weak acid and indicate the region in which the buffering capacity of the system is greatest. ANSWER: 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. 2.12). 38. What is the pH of a solution containing 0.2 M acetic acid (pKa = 4.7) and 0.1 M sodium acetate? ANSWER: pH = pKa + log [conjugate base]/[acid] pH = 4.7 + log (0.1/0.2) pH = 4.7 – 0.3 pH = 4.4 39. 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? ANSWER:
40. For a weak acid with a pKa of 6.0, show how to calculate the ratio of acid to base at pH 5. ANSWER:
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Chapter 02: Water: The Chemistry of Life 41. 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.) ANSWER: 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. This leaves 150 mM of NaOH dissolved in 500 mL of total solution, 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 M2 [H+] = 10–14 M2/0.3 M pH is, by definition, log (1/[H+]) pH = log (0.3 M/10–14 M2) = 13.48 42. 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? ANSWER: 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.
43. 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? ANSWER: 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 44. As two atoms get nearer to each other, do van der Waals attractive forces always increase? ANSWER: 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. 45. Speculate why weak forces, not strong forces, are the basis for molecular recognition among biomolecules. ANSWER: Weak forces make biological interactions reversible within physiological constraints. The Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life cumulative effects of many weak interactions can be very significant. Strong forces would require large amounts of energy to reverse any interaction. 46. 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 ANSWER: a 47. 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. ANSWER: e 48. What is the pH of a 1 M HCl solution? a. 0 b. 0.1 c. 1 d. 10 e. –1 ANSWER: a 49. What is the pH of a 0.1 M NaOH solution? a. 0.1 b. 1.0 c. 12.8 d. 13 e. 14 ANSWER: d 50. 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. Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life e. The pH can be calculated by adding 7 to the value of the pOH. ANSWER: d 51. 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 ANSWER: e 52. The aqueous solution with the lowest pH is: a. 0.01 M HCl. b. 0.1 M acetic acid (pKa = 4.76). c. 0.1 M formic acid (pKa = 3.75). d. 0.1 M HCl. e. 10–12 M NaOH. ANSWER: d 53. 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. ANSWER: d 54. 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 are correct. ANSWER: b 55. 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. Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life 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. ANSWER: e 56. "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. ANSWER: c 57. 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. ANSWER: e 58. 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 ANSWER: d 59. 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. Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life ANSWER: e 60. 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. ANSWER: d 61. 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 ANSWER: c 62. 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.
Buffer 1: Buffer 2: Buffer 3:
1 M acetic acid 10 mL 50 mL 90 mL
1 M sodium acetate 90 mL 50 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 are true. ANSWER: c 63. 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 Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life c. 9.13 d. 9.32 e. The pH cannot be determined from this information. ANSWER: a 64. The objective is to maintain a 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. ANSWER: a 65. 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 ANSWER: e Copyright Macmillan Learning. Powered by Cognero.
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Chapter 02: Water: The Chemistry of Life 66. 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 are correct. ANSWER: d
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