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Molecular Cell Biology Eighth Edition Test Bank

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    2 - 1 2 Chemical Foundations Test Bank Section 2.1 1. Covalent bonds between which of the following pairs of atoms are nonpolar? a. C – C b. C – H c. O – H d. a and b Ans: d Question Type: Multiple Choice Chapter : 2.1 Blooms: Remembering Difficulty: Easy 2. Which of the following is a noncovalent interaction? a. hydrophobic effect b. ionic interactions c. van der Waals interactions d. all of the above Ans: d Question Type: Multiple Choice Chapter : 2 Blooms: Remembering Difficulty: Easy 3. Which of the following is the strongest interaction? a. hydrogen bond b. ionic bond c. phosphoanhydride bond d. van der Waals interaction Ans: c Question Type: Multiple Choice Chapter : 2 Blooms: Understanding Difficulty: Easy 4. Which of the following is the weakest interaction? a. hydrogen bond b. ionic bond c. phosphoanhydride bond d. van der Waals interaction Ans: d Question Type: Multiple Choice

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    2 - 2 Chapter : 2 Blooms: Understanding Difficulty: Easy 5. When two atoms differing in electronegativity are joined in a covalent bond, then the : a. electrons are shared equally between the atoms. b. bond is nonpolar. c. resulting compound is devoid of any dipole moment. d. atom with the greater electronegativity attracts the bonded electrons more strongly . Ans: d Question Type: Multiple Choice Chapter : 2 Blooms: Understanding Difficulty: Moderate 6. The interactions between two proteins such as an antibody and an antigen or a hormone and its receptor are quite strong despite the fact that these interactions consist of relatively weak noncovalent bonds. How can this be? Ans: Two proteins can bind tightly because of molecular complementarity, in which multiple noncovalent bonds participate. Although each individual bond is weak, the cumulative effect of many noncovalent bonds is a relatively strong and highly specific inte raction. Question Type: Essay Chapter : 2 Blooms: Analyzing Difficulty: Moderate 7. What produces the dipole of a water molecule? Ans: The dipole of a water molecule is caused by the difference in electronegativity between O and H. The oxygen atom has a greater electronegativity than the hydrogen atom. As a result, oxygen attracts the electrons in the O – H bond more strongly , and the oxygen side of the bond has a slight net negative charge. This results in a dipole moment. Question Type: Essay Chapter : 2.1 Blooms: Understanding Difficulty: Moderate Section 2.2 8 . Which of the following is a negatively charged amino acid? a. alanine b. aspartate c. glutamine d. histidine Ans: b Question Type: Multiple Choice Chapter : 2 Blooms: Remembering Difficulty: Easy 9 . Which of the following is /are a hydrophilic amino acid? a. aspartate b. serine c. tryptophan d. aspartate and serine

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    2 - 3 Ans: d Question Type: Multiple Choice Chapter: 2 Blooms: Remembering Difficulty: Easy 10 . Adenosine is a : a. component of RNA. b. nucleo s ide. c. pyrimidine. d. a and b Ans: d Question Type: Multiple Choice Chapter: 2 Blooms: Remembering Difficulty: Moderate 1 1 . Which of the following is a monosaccharide? a. fructose b. galactose c. glucose d. all of the above Ans: d Question Type: Multiple Choice Chapter: 2 Blooms: Remembering Difficulty: Easy 1 2 . Based on what you know about hydrophobic interactions, w hich of the following is /are composed of a bilayer? a. a cell ’s membrane b. spontaneously aggregated phospholipids surrounding an aqueous interior c. lipid vesicles that have budded off the cell’s membrane d . all of the above Ans: d Question Type: Multiple Choice Chapter: 2 Blooms: Remembering Difficulty: Easy 1 3 . You discover that you suffer from a deficiency in the amino acid tryptophan. At the pharmacy, you find both D - tryptophan and L - tryptophan supplements. Which do you purchase? Why? Ans: You should choose L - tryptophan. All amino acids can exist as one of two stereoisomers ( D or L ) because of asymmetry around the α carbon. Proteins consist of the L form of amino acids, and as these stereoisomers possess distinct biological properties and are not readily interconverted, you should choose the form that is normally utilized by cells. Question Type: Essay Chapter: 2 Application Difficulty: Moderate 1 4 . Cysteine often plays an important role in stabilizing protein structure. Explain how this works.

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    2 - 4 Ans: Two adjacent sulfhydryl (SH) groups can oxidize to form a covalent disulfide (S – S) bond. Disulfide bonds can stabilize the structure of folded peptides or sometimes link two separate peptide chains together. Question Type: Essay Chapter: 2 Blooms: Understanding Difficulty: Easy 1 5. Triacylglycerol and cholesterol esters are nonpolar; in contrast, phospholipids are amphipathic molecules. Biomembranes are based on phospholipids rather than on triacylglycerols. Why? Ans: Biomembranes are based on phospholipids rather than on triacylglycerols because phospholipids as amphipathic molecules can form planar lipid bilayers, whereas the nonamphipathic nonpolar triacylglycerols cannot. The ir amphipathic property, the presence of a polar and nonpolar domain at opposite ends of the same molecule, allows phospholipids to form hydrophilic associations with water at the same time as forming hydrophobic associations with each other through their hy drophobic tails. Triacylglycerols are strictly hydrophobic in nature and hence in an aqueous environment tend to associate with one another to form lipid droplets. This minimizes the contact of triacylglycerol with water. Recall the old adage: oi l and w ater do not mix. Question Type: Essay Chapter: 2 Blooms: Evaluating Difficulty: Difficult 16 . A nucleotide can vary in _____. a. the base b. the sugar c. the phosphate group d. the sugar and the base Ans: d Question Type: Multiple Choice Chapter: 2 Blooms: Understanding Difficulty: Moderate 17 . Which of the following is NOT one of the ways RNA differs from DNA? a. Ribonucleotides have a hydroxyl group on the 2 carbon of their sugar subunit. b. Ribonucleotides can have enzymatic activity. c. Ribonucleotides contain a phosphate group. d. Ribonucleotides can contain the base uracil. Ans: c Question Type: Multiple Choice Chapter: 2 Blooms: Remembering Difficulty: Moderate 18 . What is the major structural difference between starch and cellulose? a. the types of monosaccharide subunits in the molecules b. the amount of branching that occurs in the molecule c. that humans can only ingest starch d. the type of glycosidic linkages in the molecule Ans: d Question Type: Multiple Choice

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    2 - 5 Chapter: 2 Blooms: Understanding Difficulty: Moderate 19 . How do phospholipids interact with water molecules? a. The polar heads interact with water; the nonpolar tails do not. b. Phospholipids don't interact with water because water is polar and lipids are nonpolar. c. The polar heads avoid water; the nonpolar tails attract water (because water is polar and opposites attract). d. Phospholipids dissolve in water. Ans: a Question Type: Multiple Choice Chapter: 2 Blooms: Remembering Difficulty: Easy 20 . Which of the following is the BEST explanation for why vegetable oil is a liquid at room temperature while animal fats are solid? a. Vegetable oil has fewer double bonds than animal fats. b. Animal fats have no amphipathic character. c. Vegetable oil has longer fatty - acid tails than do animal fats. d. Vegetable oil has more double bonds than do animal fats. Ans: a Question Type: Multiple Choice Chapter: 2 Blooms: Understanding Difficulty: Easy Section 2.3 21 . A 1 - mL solution of 0.05 M H 2 SO 4 is diluted to 100 mL at 25°C. What is the pH of the resulting solution? a. 1 b. 2 c. 3 d. 4 Ans: c Question Type: Multiple Choice Chapter: 2 Blooms: Applying Difficulty: Moderate 22 . An Archaea cell living in an abandoned mine is found to contain a very high concentration of protons. It is likely that thi s cell: a. has a high ph and is acidic. b. has a high ph and is alkaline. c. has low ph and is acidic. d. has a low pH and is alkaline. Ans: c Question Type: Multiple Choice Chapter: 2 Blooms: Understanding Difficulty: Easy

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    2 - 6 23. A 1 - mL solution of 0.1 M NaOH is diluted to 1 L at 25°C. What is the pH of the resulting solution? a. 1 b. 7 c. 10 d. 13 Ans: c Question Type: Multiple Choice Chapter: 2 Blooms: Applying Difficulty: Moderate 24 . The p K a of the weak base NH 3 is 9.25. When present in lysosomes, a subcellular organelle — ammonia — is almost totally protonated. Which of the pH values listed below is most likely to be that of the lysosome lumen? a. 1 b. 5 c. 8 d. 14 Ans: b Question Type: Multiple Choice Chapter: 2 Analysis Difficulty: Difficult 25 . If the equilibrium constant for the reaction A → B is 0.5 and the initial concentration of A is 25 mM and of B is 12.5 mM, then the reaction : a. will proceed in the direction it is written, producing a net increase in the concentration of B. b. will produce energy, which can be used to drive ATP synthesis. c. will proceed in the reverse direction, producing a net increase in the concentration of A. d. is at equilibrium. Ans: d Question Type: Multiple Choice Chapter: 2 Analysis Difficulty: Difficult 2 6 . For the binding reaction A + B → AB, the dissociation constant is equal to : a.      (    +    )  b. ([A] + [B])/[AB]. c. K eq d. The first and third answers are correct. Ans: b Question Type: Multiple Choice Chapter: 2 Blooms: Applying Difficulty: Easy 2 7 . What is the effect of an enzyme on the end equilibrium concentration of reactants and products?

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    2 - 7 Ans: An enzyme has no effect on the end equilibrium concentration of reactants and products. Question Type: Essay Chapter: 2 Blooms: Analyzing Difficulty: Easy 2 8 . The enzyme alcohol dehydrogenase is capable of catalyzing the oxidation of a number of different substances, including ethanol, ethylene glycol, and methanol, to an aldehyde. The metabolic products of both ethylene glycol and methanol are highly toxic to humans. A standard medical treatment for prevention of ethylene glycol or methanol poisoning is the administration of a dose of ethanol. Why is this treatment effective? Ans: The ethanol - like ethylene glycol and methanol are capable of binding to the enzyme, alcohol dehydrogenase, and compet ing with its other substrates. A sufficient dosage of ethanol can out - compete the other substrates, and hence the ethylene glycol and methanol are not metabolized to toxic products. Gradually the ethylene glycol or methanol will be excreted from the body. Question Type: Essay Chapter: 2 Blooms: Evaluating Difficulty: Moderate 2 9 . How do cells maintain a relatively constant pH despite the fact that many metabolic processes produce acids? Ans: All cells contain buffers such as phosphate ions that can absorb or release protons or hydroxyl ions to stabilize pH cha nges near neutral pH. Question Type: Essay Chapter: 2 Blooms: Evaluating Difficulty: Difficult Section 2.4 30 . In a biochemical reaction in which  H < 0 and  S > 0 : a. the reaction is spontaneous. b. the reaction is endothermic. c. the reaction is endergonic. d.  G is positive. Ans: a Question Type: Multiple Choice Chapter: 2 Blooms: Applying Difficulty: Easy 31 . In the reaction NAD + + H + + 2 e − → NADH, NAD + becomes : a. dehydrated. b. hydrolyzed. c. oxidized. d. reduced. Ans: d Question Type: Multiple Choice Chapter: 2 Blooms: Understanding Difficulty: Easy 32 . The ultimate source of chemical energy for all cells is :

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    2 - 8 a. electricity. b. heat. c. light. d. magnetism. Ans: c Question Type: Multiple Choice Chapter: 2 Blooms: Applying Difficulty: Moderate 33 . Hydrolysis of ATP : a. is endothermic. b. has a positive G value. c. must be coupled to an energetically favorable reaction. d. none of the above Ans: d Question Type: Multiple Choice Chapter: 2 Blooms: Understanding Difficulty: Easy 34 . What is [P]/[R] when  G =  G °´? a. – 1 b. 0 c. 1 d. 2.3 Ans: c Question Type: Multiple Choice Chapter: 2 Blooms: Applying Difficulty: Moderate 35 . A reaction with a positive  G value can be made energetically favorable by increasing the : a.  G   . b. starting concentration of products. c. starting concentration of reactants. d. The first two answers are correct. Ans: c Question Type: Multiple Choice Chapter: 2 Blooms: Analyzing Difficulty: Moderate 36 . Photosynthesis by plants and certain microbes traps the energy in light and uses it to : a. reduce glucose into carbon dioxide. b. synthesize ATP from ADP and inorganic phosphate. c. generate ATP from the oxidation of reduced inorganic compounds. d. none of the above Ans: b Question Type: Multiple Choice Chapter: 2

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    2 - 9 Blooms: Understanding Difficulty: Moderate 3 7 . NAD + and FAD are often referred to as : a. redox proteins. b. polymers. c. reduced dinucleotides. d. electron - carrying coenzymes. Ans: d Question Type: Multiple Choice Chapter: 2 Blooms: Remembering Difficulty: Easy 3 8 . A solution of 8 M urea is sometimes used in the isolation of protein molecules. When the solution is prepared by dissolvi ng urea in water at room temperature, it becomes cold. How should the G for this process change if you tried to dissolve urea in the cold room, rather than at room temperature? Ans: Urea will be less soluble at cold temperatures than at room temperature because the decrease in temperature will decreas e the term T  S , increasing the value of  G , because  G =  H − T  S . The values of  H and  S are relatively independent of temperature. Question Type: Essay Chapter: 2 Blooms: Analyzing Difficulty: Moderate 3 9 . Phosphoglucomutase converts glucose 1 - phosphate, the product of the reaction catalyzed by glycogen phosphorylase, into glucose 6 - phosphate. The K eq for this reaction is 19 under standard conditions. What is the G °´ for the reaction? Ans: −1.741 kcal/mol,  G °´ = −2.3 RT log K eq ,  G °´ = −2.3 (1.987) (298) log K eq Question Type: Essay Chapter: 2 Application Difficulty: Moderate 40 . Under what conditions is the  G for a reaction different from the  G °´? Ans:  G °´ is the Gibbs free energy of a reaction under standard conditions: pH 7.0, 1 M initial concentration of all reactants and products except protons and water, 1 atm pressure, 298°K (25°C). Variation of any of these parameters from standard conditions, dep ending on the reaction, can produce a different  G value. Question Type: Essay Chapter: 2 Blooms: Understanding Difficulty: Easy 41 . The amount of free energy released when bonds are broken during a reaction is higher when the molecule has more electronegative atoms. Ans: False Question Type: True/False Chapter: 2 Blooms: Applying Difficulty: Moderate

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    2 - 10 42 . Which of the following is true about an observed change in free energy (  G )? a. Free energy was created when the Big Bang occurred. b. It can be calculated from the total change in energy, temperature, and change in entropy. c. If a reaction's free energy is greater than zero, it is likely to happen spontaneously. d. Free energy is comparable to unusable energy. Ans: b Question Type: Multiple Choice Chapter: 2 Blooms: Understanding Difficulty: Easy

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    3 - 1 3 Section 3.1 1. Which of the following is defined as the tertiary structure of a protein? a. the primary amino acid sequence b. structural domains such as a DNA - binding domain c. folded structures such as an α helix d. structural features such as a turn Ans: b Question Type: Multiple Choice Chapter: 3 Blooms: Understanding Difficulty: Easy 2. Monomeric proteins do not contain a : a. primary structure. b. secondary structure. c. tertiary structure. d. quaternary structure. Ans: d Question Type: Multiple Choice Chapter: 3 Blooms: Understanding Difficulty: Easy 3. Which of the following is NOT part of a zinc - finger motif? a. zinc ion b. proline residue c. cysteine residue d. histidine residue Ans: b Question Type: Multiple Choice Chapter: 3 Blooms: Remembering Difficulty: Easy 4 . Describe the types of bonds/interactions that hold together or stabilize the primary, secondary, tertiary, and quaternary structures of proteins. Ans: The primary structure of a protein is linked by covalent peptide bonds. The secondary structure is stabilized by hydrogen bonds between atoms of the peptide backbone. The tertiary structure is stabilized by hydrophobic Protein Structure and Function

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    3 - 2 interactions between the nonpolar side groups and hydrogen bonds between polar side groups. The quaternary structure is held together by noncovalent bonds between protein subunits. Question Type: Essay Chapter: 3 Blooms: Understanding Difficulty: Easy 5 . Many proteins contain one or more motifs built from particular combinations of secondary structure. Describe the three common structural motifs discussed in this chapter. Ans: The three structural motifs described in this chapter include the coiled coil motif, the helix - loop - helix motif, and the zinc finger motif. The coiled - coil motif consists of two or more  helices wrapped around one another. The helix - loop - helix motif consists of two helices connected by a loop that contains certain hydrophilic residues at invariant positions in the loop. The zinc - finger motif consists of an  helix and two  strands held together by a zinc ion in a fingerlike bundle. Question Type: Essay Chapter: 3 Application Difficulty: Moderate 6. What types of bonds are apt to be more common in the nonaqueous, interior environment of a protein than in the aqueous, surface environment of a protein? Ans: Proteins are arranged so that hydrophilic amino acids are on the surface of the protein and hydrophobic amino acids are in the interior. Hence, hydrogen bonding and ionic interactions with water are particularly common at the protein surface; hydrophobic interactions are more common in the protein interior. Question Type: Essay Chapter: 3 Blooms: Applying Difficulty: Moderate 7. There are many important roles for the dynamic nature of proteins in a cell. Which of the following is NOT likely to describe one such reason? a. A protein’s structure determines its function. b. Other molecules could be needed to allow proteins to fold into their active (ordered) conformation. c. Quaternary structures are usually very transient (occur for short periods of time). d. Proteins are crucial for many cell functions. Ans: c Question Type: Multiple Choice Chapter: 3 Blooms: Applying Difficulty: Moderate 9. You are studying an oligopeptide composed of eight amino acids. The four amino acids nearest the C terminus are nonpolar. The two amino acids nearest the N terminus are charged. The middle two amino acids are polar. Which amino acid is likely to be labeled as number 2? a . threonine b . phenylalanine c. glutamine d. lysine Ans: d Question Type: Multiple Choice Chapter: 3

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    3 - 3 Blooms: Applying Difficulty: Moderate 10. A protein containing several proline residues is: a. not likely to form quarternary structures . b. likely to be an integral membrane protein . c. not likely to form alpha helices . d. likely to be found in beta turns . Ans: c Question Type: Multiple Choice Chapter: 3 Blooms: Remembering Difficulty: Moderate 11. Which of the following is true about protein folding? a. Amino acids cluster in the primary sequence so that all the hydrophobic amino acids are near each other to facilitate folding into the hydrophobic core of the tertiary structure . b. A ll known proteins have well - ordered conformations . c. A mino acids with hydrophobic, nonpolar side chains stabilize the tertiary structure through hydrogen bonding with water molecules surrounding the proteins . d. E lements from the secondary structure are maintained in the tertiary structure . Ans: d Question Type: Multiple Choice Chapter: 3 Blooms: Understanding Difficulty: Moderate 12. When comparing domains and structural motifs, which of the following is NOT true? a. M otifs are found in secondary structures, while domains are found in tertiary structures . b. H elices are observed in motifs and domains . c. S tructural domains appear in different proteins with similar functions, while structural motifs have been less conserved over evolution . d. A domain may be repeated in the same protein, but multiple copies of the same motif are rare . Ans: c Question Type: Multiple Choice Chapter: 3 Blooms: Understanding Difficulty: Moderate 13. You disrupt all hydrogen bonds in a protein. What level of structure will be preserved? a. secondary structure b. primary structure c. tertiary structure d. quaternary structure Ans: b Question Type: Multiple Choice Chapter: 3 Blooms: Understanding Difficulty: Easy 14. Two proteins that have a similar function : a. will share similar amino acid sequences if they are homologs .

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    3 - 4 b. must have similar amino acid sequences . c. will have identical primary structures . d. belong in families together . Ans: a Question Type: Multiple Choice Chapter: 3 Blooms: Remembering Difficulty: Moderate Section 3.2 15 . All the following statements about molecular chaperones are true EXCEPT: a. t hey play a role in the proper folding of proteins. b. t hey are located in every cellular compartment. c. t hey are found only in mammals. d. t hey bind a wide range of proteins. Ans: c Question Type: Multiple Choice Chapter 3.2 Blooms: Understanding Difficulty: Easy 16 . Hsp90 family members are present in all organisms EXCEPT : a. a rchaea . b. b acteria . c. fungi . d. plants . Ans: a Question Type: Multiple Choice Chapter 3.2 Blooms: Remembering Difficulty: Easy 17 . Describe the mechanism by which the bacterial chaperonin GroEL promotes protein folding. Ans: The bacterial chaperonin GroEL forms a barrel - shaped complex of 14 identical subunits. A partially folded or misfolded polypeptide is inserted into the GroEL barrel, where it binds to the inner wall and folds into its native conformation. In an ATP - dependent step, the GroEL barrel expands to a more open state, which results in release of the folded protein. Question Type: Essay Chapter 3.2 Blooms: Understanding Difficulty: Moderate 18 . What role does aberrant protein folding play in the development of a disease such as Alzheimer’s disease? Ans: Misfolding of a protein marks it for degradation by proteolytic cleavage. In Alzheimer’s disease, misfolding and subsequent proteolytic degradation of the amyloid precursor protein generates a short fragment called  - amyloid protein, which changes from an  - helical to a  - sheet conformation. This aberrant structure aggregates into highly stable filaments called amyloid plaques that accumulate in the brains of Alzheimer’s patients. Question Type: Essay Chapter 3.2 Blooms: Understanding

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    3 - 5 Difficulty: Easy 19. Which of the following does NOT impose limits on protein folding? a. ability of side chains to form hydrogen and ionic bonds b. backbone sequence of the polypeptide c. rotations of the planes around the peptide bonds d. size of side chains Ans: b Question Type: Multiple Choice Chapter 3.2 Blooms: Remembering Difficulty: Easy 20 . Eggs are protein - rich foods. An uncooked egg can catalyze a reaction that breaks down bacterial cell walls. After cooking, this activity is almost abolished. This is likely because: a. the enzyme became denatured . b . bacteria can grow on cooked eggs . c . the cell membranes were liquefied. d. cooking sped up chemical reactions . Ans: a Question Type: Multiple Choice Section 3.2 Blooms: Understanding Difficulty: Moderate 21 . The correct order for molecular chaperone – mediated protein folding is: I – exchange of ATP for ADP on chaperone II – chaperone undergoes conformational change, which a ffects protein folding III – chaperone binds to exposed hydrophobic residues on unfolded protein IV – folded protein is released a. I, II, III, IV b. III, II, I, IV c. III, I, II, IV d. II, III, I, IV Ans: b Question Type: Multiple Choice Section 3.2 Blooms: Understanding Difficulty: Easy Section 3.3 22 . All the following statements about enzymes are true EXCEPT : a. t hey function in an aqueous environment. b. t hey lower the activation energy of a reaction. c. t hey increase the rate of a reaction. d. a single enzyme typically react s with many different substrates. Ans: d Question Type: Multiple Choice Chapter 3.3 Blooms: Understanding Difficulty: Easy

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