Test 3
13-11 In step 4 of glycolysis, a six-carbon sugar (fructose 1,6-bisphosphate) is cleaved to produce two three-carbon molecules (dihydroxyacetone phosphate and glyceraldehyde 3-phosphate). Which enzyme catalyzes this reaction? (a) aldolase (b) phosphoglucose isomerase (c) enolase (d) triose phosphate isomerase
A
13-12 The conversion of glyceraldehyde 3-phosphate to 1,3 bisphosphoglycerate in step 6 of glycolysis generates a "high energy" phosphoanhydride bond. Which of the following best describes what happens to that bond in step 7? (a) It is hydrolyzed to drive the formation of ATP. (b) It is hydrolyzed to drive the formation of NADH. (c) It is hydrolyzed to generate pyruvate. (d) It is oxidized to CO2.
A
13-15 Several different classes of enzymes are needed for the catabolism of carbohydrates. Which of the following descriptions best matches the function of an isomerase? (a) An enzyme that catalyzes the rearrangement of bonds within a single molecule. (b) An enzyme that catalyzes a change in the position of a specific chemical group within a single molecule. (c) An enzyme that catalyzes the oxidation of a molecule by removing a hydride ion. (d) An enzyme that catalyzes the addition of phosphate groups to other molecules.
A
13-2 Glycolysis is an anaerobic process used to catabolize glucose. What does it mean for this process to be anaerobic? (a) no oxygen is required (b) no oxidation occurs (c) it takes place in the lysosome (d) glucose is broken down by the addition of electrons
A
13-23 What purpose does the phosphorylation of glucose to glucose 6-phosphate by the enzyme hexokinase serve as the first step in glycolysis? (a) It helps drive the uptake of glucose from outside the cell. (b) It generates a high-energy phosphate bond. (c) It converts ATP to a more useful form. (d) It enables the glucose 6-phosphate to be recognized by phosphofructokinase, the next enzyme in the glycolytic pathway.
A
13-25 Which of the following cells rely exclusively on glycolysis to supply them with ATP? (a) anaerobically growing yeast (b) aerobic bacteria (c) skeletal muscle cells (d) plant cells
A
13-27 Select the best option to fill in the blanks of the following statement: Fermentation is a/an _____________________ process that converts _____________ into carbon dioxide and _____________________. (a) anaerobic, pyruvate, ethanol (b) anaerobic, lactate, ethanol (c) eukaryotic, glyceraldehyde 3-phosphate, ethanol (d) prokaryotic, lactate, propanol
A
13-35 The citric acid cycle is a critical sequence of reactions for energy production, which take place in the matrix of the mitochondria. The reaction cycle requires materials from the cytosol to be converted into acetyl CoA, which represents the starting point of a new cycle. Which of the following statements about acetyl CoA is true? (a) Amino acids can be converted into acetyl CoA. (b) Pyruvate is converted into acetyl CoA in the cytosol. (c) Triacylglycerol molecules are transported into the mitochondrial matrix and cleaved by lipases to produce acetyl CoA. (d) Oxaloacetate is converted directly into acetyl CoA to feed the citric acid cycle.
A
13-40 The citric acid cycle is a series of oxidation reactions that removes carbon atoms from substrates in the form of CO2. Where do the oxygen atoms in the carbon dioxide molecules come from? (a) water (b) phosphates (c) molecular oxygen (d) acetyl CoA
A
13-49 In step 4 of the citric acid cycle, the reduction of NAD+ to NADH is coupled to the generation of CO2 and the formation of a high-energy thioester bond. The energy of the thioester bond is harnessed in step 5. What is the energy used for? (a) to generate a molecule of GTP (b) to generate a molecule of ATP (c) to generate a proton gradient (d) to generate a molecule of NADH
A
13-54 The oxygen-dependent reactions required for cellular respiration were originally thought to occur in a linear pathway. By using a competitive inhibitor for one enzyme in the pathway, investigators discovered that these reactions occur in a cycle. What compound served as the inhibitor? (a) malonate (b) malate (c) fumarate (d) succinate
A
13-60 In the final stage of the oxidation of food molecules, a gradient of protons is formed across the inner mitochondrial membrane, which is normally impermeable to protons. If cells were exposed to an agent that causes the membrane to become freely permeable to protons, which of the following effects would you expect to observe? (a) The ratio of ATP to ADP in the cytoplasm would fall. (b) NADH would build up. (c) Carbon dioxide production would cease. (d) The consumption of oxygen would fall.
A
13-63 When glucose is being used up and not replaced from food intake, the blood sugar level can be maintained by synthesizing glucose from smaller molecules such as pyruvate or lactate. This process is called gluconeogenesis. Which organ is principally responsible for supplying glucose to the rest of the body when glucose reserves are low? (a) liver (b) pancreas (c) spleen (d) gall bladder
A
13-7 Foods are broken down into simple molecular subunits for distribution and use throughout the body. Which type of simple subunits, listed below, is used preferentially as an energy source? (a) simple sugars (b) proteins (c) free fatty acids (d) glycerol
A
15-12 Proteins that are fully translated in the cytosol and lack a sorting signal will end up in ____. (a) the cytosol. (b) the mitochondria. (c) the interior of the nucleus. (d) the nuclear membrane.
A
15-14 What is the role of the nuclear localization sequence in a nuclear protein? (a) It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore. (b) It is a hydrophobic sequence that enables the protein to enter the nuclear membranes. (c) It aids in protein unfolding so that the protein can thread through nuclear pores. (d) It prevents the protein from diffusing out of the nucleus through nuclear pores.
A
15-16 A large protein that passes through the nuclear pore must have an appropriate _________. (a) sorting sequence, which typically contains the positively charged amino acids lysine and arginine. (b) sorting sequence, which typically contains the hydrophobic amino acids leucine and isoleucine. (c) sequence to interact with the nuclear fibrils. (d) Ran-interacting protein domain.
A
15-2 Which of the following statements about membrane-enclosed organelles is true? (a) In a typical cell, the area of the endoplasmic reticulum membrane far exceeds the area of plasma membrane. (b) The nucleus is the only organelle that is surrounded by a double membrane. (c) Other than the nucleus, most organelles are small and thus, in a typical cell, only about 10% of a cell's volume is occupied by membrane-enclosed organelles; the other 90% of the cell volume is the cytosol. (d) The nucleus is the only organelle that contains DNA.
A
15-21 Which of the following statements about peroxisomes is false? (a) Most peroxisomal proteins are synthesized in the ER. (b) Peroxisomes synthesize phospholipids for the myelin sheath. (c) Peroxisomes produce hydrogen peroxide. (d) Vesicles that bud from the ER can mature into peroxisomes.
A
15-38 Which of the following statements about vesicle budding from the Golgi is false? (a) Clathrin molecules are important for binding to and selecting cargoes for transport. (b) Adaptins interact with clathrin. (c) Once vesicle budding occurs, clathrin molecules are released from the vesicle. (d) Clathrin molecules act at the cytosolic surface of the Golgi membrane.
A
15-56 Which of the following statements about secretion is true? (a) The membrane of a secretory vesicle will fuse with the plasma membrane when it discharges its contents to the cell's exterior. (b) Vesicles for regulated exocytosis will not bud off the trans Golgi network until the appropriate signal has been received by the cell. (c) The signal sequences of proteins destined for constitutive exocytosis ensure their packaging into the correct vesicles. (d) Proteins destined for constitutive exocytosis aggregate as a result of the acidic pH of the trans Golgi network.
A
15-61 Which of the following statements about phagocytic cells in animals is false? (a) Phagocytic cells are important in the gut to take up large particles of food. (b) Phagocytic cells scavenge dead and damaged cells and cell debris. (c) Phagocytic cells can engulf invading microorganisms and deliver them to their lysosomes for destruction. (d) Phagocytic cells extend pseudopods that surround the material to be ingested.
A
17-20 Which of the following statements about the function of the centrosome is false? (a) Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome. (b) Centrosomes contain hundreds of copies of the γ-tubulin ring complex important for microtubule nucleation. (c) Centrosomes typically contain a pair of centrioles, which is made up of a cylindrical array of short microtubules. (d) Centrosomes are the major microtubule-organizing center in animal cells.
A
17-21 Which of the following statements about microtubules is true? (a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament. (b) The centromere nucleates the microtubules of the mitotic spindle. (c) Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell. (d) ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule.
A
17-29 Which of the situations below will enhance microtubule shrinkage? (a) addition of a drug that inhibits GTP exchange on free tubulin dimers (b) addition of a drug that inhibits hydrolysis of the GTP carried by tubulin dimers (c) addition of a drug that increases the affinity of tubulin molecules carrying GDP for other tubulin molecules (d) addition of a drug that blocks the ability of a tubulin dimer to bind to γ-tubulin
A
17-31 The graph in Figure Q17-31 shows the time course of the polymerization of pure tubulin in vitro. Assume that the starting concentration of free tubulin is higher than it is in cells. Three parts of the curve are labeled above it as A, B, and C. You conduct a similar in vitro tubulin-polymerization experiment, only you include purified centrosomes in your preparation. When you plot your data, which part of your graph should be most dissimilar to the curve shown in Figure Q17-31? (a) A (b) B (c) C (d) None. The shape of my graph should be identical to the graph produced when tubulin is polymerized in the absence of purified centrosomes.
A
17-39 Which of the following items is not important for flagellar movement? (a) sarcoplasmic reticulum (b) ATP (c) dynein (d) microtubules
A
17-46 Compared to the normal situation, in which actin monomers carry ATP, what do you predict would happen if actin monomers that bind a nonhydrolyzable form of ATP were incorporated into actin filaments? (a) Actin filaments would grow longer. (b) Actin filaments would grow shorter because depolymerization would be enhanced. (c) Actin filaments would grow shorter because new monomers could not be added to the filaments. (d) No change, as addition of monomers binding nonhydrolyzable ATP would not affect actin filament length.
A
17-8 All intermediate filaments are of similar diameter because ____________. (a) the central rod domains are similar in size and amino acid sequence. (b) the globular domains are similar in size and amino acid sequence. (c) covalent bonds among tetramers allow them to pack together in a similar fashion. (d) there is only a single type of intermediate filament in every organism.
A
15-31 Figure Q15-31 shows the organization of a protein that resides on the ER membrane. The N- and C-termini of the protein are labeled. Boxes 1, 2, and 3 represent membrane-spanning sequences. Non-membrane-spanning regions of the protein are labeled "X," "Y," and "Z."
A. in the cytoplasm
13-13 Steps 7 and 10 of glycolysis result in substrate-level phosphorylation. Which of the following best describes this process? (a) ATP is being hydrolyzed to phosphorylate the substrate. (b) The energy derived from substrate oxidation is coupled to the conversion of ADP to ATP. (c) Two successive phosphates are transferred, first to AMP, then to ADP, finally forming ATP. (d) The substrate is hydrolyzed using ATP as an energy source.
B
13-16 Several different classes of enzymes are needed for the catabolism of carbohydrates. Which of the following descriptions best matches the function of a mutase? (a) An enzyme that catalyzes the rearrangement of bonds within a single molecule. (b) An enzyme that catalyzes a change in the position of a specific chemical group within a single molecule. (c) An enzyme that catalyzes the oxidation of a molecule by removing a hydride ion. (d) An enzyme that catalyzes the addition of phosphate groups to other molecules.
B
13-30 The first energy-generating steps in glycolysis begin when glyceraldehyde 3-phosphate undergoes an energetically favorable reaction in which it is simultaneously oxidized and phosphorylated by the enzyme glyceraldehyde 3-phosphate dehydrogenase to form 1,3-bisphosphoglycerate, with the accompanying conversion of NAD+ to NADH. In a second energetically favorable reaction catalyzed by a second enzyme, the 1,3-bisphosphoglycerate is then converted to 3-phosphoglycerate, with the accompanying conversion of ADP to ATP. Which of the following statements is true about this reaction? (a) The reaction glyceraldehyde 3-phosphate í 1,3-bisphosphoglycerate should be inhibited when levels of NADH fall. (b) The ΔG° for the oxidation of the aldehyde group on glyceraldehyde 3-phosphate to form a carboxylic acid is more negative than the ΔG° for ATP hydrolysis. (c) The energy stored in the phosphate bond of glyceraldehyde 3-phosphate contributes to driving the reaction forward. (d) The cysteine side chain on the enzyme is oxidized by NAD+.
B
13-31 The simultaneous oxidation and phosphorylation of glyceraldehyde 3-phosphate forms a highly reactive covalent thioester bond between a cysteine side chain (reactive group -SH) on the enzyme (glyceraldehyde 3-phosphate dehydrogenase) and the oxidized intermediate (see arrow in Figure Q13-31A). If the enzyme had a serine (reactive group -OH) instead of a cysteine at this position, which could form only a much-lower-energy bond to the oxidized substrate (see arrow in Figure Q13-31B), how might this new enzyme act?(a) It would oxidize the substrate and phosphorylate it without releasing it. (b) It would oxidize the substrate but not release it. (c) It would phosphorylate the substrate on the 2 position instead of the 1 position. (d) It would behave just like the normal enzyme.
B
13-41 Fatty acids can easily be used to generate energy for the cell. Which of the following fatty acids will yield more energy? Explain your answer. (a) CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH=CH-COOH (b) CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH (c) CH3-CH=CH-CH2-CH2-CH2-CH2-CH=CH-COOH (d) CH3-CH2-CH2-CH2-CH2-CH2-CH2-COOH
B
13-50 Step 6 of the citric acid cycle is catalyzed by succinate dehydrogenase. Keeping in mind that dehydrogenases catalyze redox reactions, which are the products of the reaction in which succinate is oxidized? (a) fumarate, NADH (b) fumarate, FADH2 (c) fumarate, FADH2 (d) succinyl CoA, NADH
B
13-52 In the final step of the citric acid cycle, oxaloacetate is regenerated through the oxidation of malate and this is coupled with the production of which other molecule? (a) FADH (b) NADH (c) GTP (d) CO2
B
13-56 The oxygen-dependent reactions required for cellular respiration were originally thought to occur in a linear pathway. By using a competitive inhibitor for one enzyme in the pathway, investigators discovered that these reactions occur in a cycle. Which product in the reaction pathway builds up when the inhibitor is added? (a) citrate (b) succinate (c) fumarate (d) malate
B
13-66 Which of the following polymers of glucose is used as a vehicle to store energy reserves in animal cells? (a) glucagon (b) glycogen (c) starch (d) glycerol
B
13-69 In humans, glycogen is a more useful food-storage molecule than fat because _____________________. (a) a gram of glycogen produces more energy than a gram of fat. (b) it can be utilized to produce ATP under anaerobic conditions, whereas fat cannot. (c) it binds water and is therefore useful in keeping the body hydrated. (d) for the same amount of energy storage, glycogen occupies less space in a cell than does fat.
B
13-70 The concentration of H+ ions inside the mitochondrial matrix is lower than it is in the cytosol or the mitochondrial intermembrane space. What would be the immediate effect of a membrane-permeable compound that carries and releases protons into the mitochondrial matrix? (a) inhibition of the electron-transport chain (b) inhibition of ATP synthesis (c) increased import of ADP into the matrix (d) inhibition of the citric acid cycle
B
13-8 The final metabolite produced by glycolysis is ___________. (a) acetyl CoA. (b) pyruvate. (c) 3-phosphoglycerate. (d) glyceraldehyde 3-phosphate.
B
15-1 Which of the following statements about the endoplasmic reticulum (ER) is false? (a) The ER is the major site for new membrane synthesis in the cell. (b) Proteins to be delivered to the ER lumen are synthesized on smooth ER. (c) Steroid hormones are synthesized on the smooth ER. (d) The ER membrane is contiguous with the outer nuclear membrane.
B
15-20 Which of the following statements about transport into mitochondria and chloroplasts is false? (a) The signal sequence on proteins destined for these organelles is recognized by a receptor protein in the outer membrane of these organelles. (b) After a protein moves through the protein translocator in the outer membrane of these organelles, the protein diffuses in the lumen until it encounters a protein translocator in the inner membrane. (c) Proteins that are transported into these organelles are unfolded as they are being transported. (d) Signal peptidase will remove the signal sequence once the protein has been imported into these organelles.
B
15-39 Molecules to be packaged into vesicles for transport are selected by (a) clathrin. (b) adaptins. (c) dynamin. (d) SNAREs.
B
15-42An individual transport vesicle (a) contains only one type of protein in its lumen. (b) will fuse with only one type of membrane. (c) is endocytic if it is traveling toward the plasma membrane. (d) is enclosed by a membrane with the same lipid and protein composition as the membrane of the donor organelle.
B
15-51 Which of the following statements about the protein quality control system in the ER is false? (a) Chaperone proteins help misfolded proteins fold properly. (b) Proteins that are misfolded are degraded in the ER lumen. (c) Protein complexes are checked for proper assembly before they can exit the ER. (d) A chaperone protein will bind to a misfolded protein to retain it in the ER.
B
15-64 You are working in a biotech company that has discovered a small-molecule drug called H5434. H5434 binds to LDL receptors when they are bound to cholesterol. H5434 binding does not alter the conformation of the LDL receptor's intracellular domain. Interestingly, in vitro experiments demonstrate that addition of H5434 increases the affinity of LDL for cholesterol and prevents cholesterol from dissociating from the LDL receptor even in acidic conditions. Which of the following is a reasonable prediction of what may happen when you add H5434 to cells? (a) Cytosolic cholesterol levels will remain unchanged relative to normal cells. (b) Cytosolic cholesterol levels will decrease relative to normal cells. (c) The LDL receptor will remain on the plasma membrane. (d) The uncoating of vesicles will not occur.
B
15-8 Which of the following statements is true? (a) Lysosomes are believed to have originated from the engulfment of bacteria specialized for digestion. (b) The nuclear membrane is thought to have arisen from the plasma membrane invaginating around the DNA. (c) Because bacteria do not have mitochondria, they cannot produce ATP in a membrane-dependent fashion. (d) Chloroplasts and mitochondria share their DNA.
B
17-10 Intermediate filaments are made from elongated fibrous proteins that are assembled into a ropelike structure. Figure Q17-10 shows the structure of an intermediate filament subunit. You are interested in how intermediate filaments are formed, and you create an intermediate filament subunit whose α-helical region is twice as long as that of a normal intermediate filament by duplicating the normal α-helical region while keeping a globular head at the N-terminus and a globular tail at the C-terminus; you call this subunit IFαd. If you were to assemble intermediate filaments using IFαd as the subunit, which of the following predictions describes the most likely outcome?(a) Filaments assembled using IFαd will interact with different cytoskeletal components. (b) Filaments assembled using IFαd will form dimers that are twice as long as dimers assembled from normal intermediate filaments. (c) Sixteen tetramers assembled from IFαd will be needed for a ropelike structure to form. (d) Dimers of IFαd will form by interactions with the N-terminal globular head and the C-terminal globular tail.
B
17-26 You discover a protein, MtA, and find that it binds to the plus ends of microtubules in cells. The hypothesis that best explains this localization is ________________. (a) MtA is involved in stabilizing microtubules. (b) MtA binds to GTP-bound tubulin on microtubules. (c) MtA is important for the interaction of microtubules with the centrosome. (d) MtA will not bind to purified microtubules in a test tube.
B
17-32 Which of the following statements about organellar movement in the cell is false? (a) Organelles undergo saltatory movement in the cell. (b) Only the microtubule cytoskeleton is involved in organellar movement. (c) Motor proteins involved in organellar movement use ATP hydrolysis for energy. (d) Organelles are attached to the tail domain of motor proteins.
B
17-44 Consider the mechanism by which actin and tubulin polymerize. Which of the items below does not describe something similar about the polymerization mechanisms of actin and microtubules? (a) Although both filaments can grow from both ends, the growth rate is faster at the plus ends. (b) Depolymerization initiates at the plus ends of filaments. (c) Nucleotide hydrolysis promotes depolymerization of filaments. (d) Free subunits (actin and tubulin) carry nucleoside triphosphates.
B
17-49 Which of the following statements is false? (a) Cytochalasins prevent actin polymerization. (b) Actin filaments are usually excluded from the cell cortex. (c) Integrins are transmembrane proteins that can bind to the extracellular matrix. (d) ARPs can promote the formation of branched actin filaments.
B
17-57 Figure Q17-57shows an electron micrograph of a skeletal muscle fiber, where various points along a fiber and various regions have been labeled.Which of the following statements is true about muscle contraction? (a) Point A will move closer to point B. (b) Point B will move closer to point C. (c) Region D will become smaller. (d) Region E will shrink in size.
B
17-58 Which of the following conditions is likely to decrease the likelihood of skeletal muscle contraction? (a) partial depolarization of the T-tubule membrane, such that the resting potential is closer to zero (b) addition of a drug that blocks Ca2+ binding to troponin (c) an increase in the amount of ATP in the cell (d) a mutation in tropomyosin that decreases its affinity for the actin filament
B
17-59 Which of the following statements about skeletal muscle contraction is false? (a) When a muscle cell receives a signal from the nervous system, voltage-gated channels open in the T-tubule membrane. (b) The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction. (c) A change in the conformation of troponin leads to changes in tropomyosin such that it no longer blocks the binding of myosin heads to the actin filament. (d) During muscle contraction, the Z discs move closer together as the myosin heads walk toward the plus ends of the actin filaments.
B
17-9 Intermediate filaments help protect animal cells from mechanical stress because ____________. (a) filaments directly extend from the interior of the cell to the extracellular space and into the next cell, linking one cell to the next, helping to distribute locally applied forces. (b) filaments in each cell are indirectly connected to the filaments of a neighboring cell through the desmosome, creating a continuous mechanical link between cells. (c) filaments remain independent of other cytoskeletal elements and keep the mechanical stress away from other cellular components. (d) filaments make up the desmosome junctions that connect cells; these junctions are more important than the internal network of filaments for protecting cells against mechanical stress.
B
13-32 In the absence of oxygen, yeast cells can switch to a completely anaerobic metabolism called fermentation. Which of the following is a final product of fermentation in yeast?
B, ethanol
15-34 Figure Q15-34 shows the organization of a protein that normally resides in the plasma membrane. The boxes labeled 1 and 2 represent membrane-spanning sequences and the arrow represents a site of action of signal peptidase. Given this diagram, which of the following statements must be true?
B. The C-terminus of this protein is cytoplasmic.
13-10 Which of the following steps or processes in aerobic respiration include the production of carbon dioxide? (a) breakdown of glycogen (b) glycolysis (c) conversion of pyruvate to acetyl CoA (d) oxidative phosphorylation
C
13-17 Several different classes of enzymes are needed for the catabolism of carbohydrates. Which of the following descriptions best matches the function of a dehydrogenase? (a) An enzyme that catalyzes the rearrangement of bonds within a single molecule. (b) An enzyme that catalyzes a change in the position of a specific chemical group within a single molecule. (c) An enzyme that catalyzes the oxidation of a molecule by removing a hydride ion. (d) An enzyme that catalyzes the addition of phosphate groups to other molecules.
C
13-22 Which reaction does the enzyme phosphoglucose isomerase catalyze? (a) glucose í glucose 6-phosphate (b) fructose 6-phosphate í fructose 1,6-bisphosphate (c) glucose 6-phosphate í fructose 6-phosphate (d) glucose í glucose 1-phosphate
C
13-26 In anaerobic conditions, skeletal muscle produces _____________. (a) lactate and CO2. (b) ethanol and CO2. (c) lactate only. (d) ethanol only.
C
13-29 Glyceraldehyde 3-phosphate dehydrogenase operates by stripping a hydride ion from its substrate. Which molecule is the recipient of the proton and two electrons during this transfer? (a) oxygen (b) acetyl CoA (c) NAD+ (d) FADH
C
13-39 The reaction cycle that uses acetyl CoA to generate electron carrier molecules needed in the electron-transport chain is important for powering the cell. Which of the names below is not one of those commonly used to describe this reaction cycle? (a) tricarboxylic acid cycle (b) Krebs cycle (c) oxaloacetic acid cycle (d) citric acid cycle
C
13-4 The advantage to the cell of the gradual oxidation of glucose during cellular respiration compared with its combustion to CO2 and H2O in a single step is that ________________. (a) more free energy is released for a given amount of glucose oxidized. (b) no energy is lost as heat. (c) energy can be extracted in usable amounts. (d) more CO2 is produced for a given amount of glucose oxidized.
C
13-45 In step 1 of the citric acid cycle, citrate is generated by the enzyme citrate synthase. The enzyme combines the two-carbon acetyl group from acetyl CoA and the four-carbon oxaloacetate. What is the source of energy that drives this reaction forward? (a) a high-energy phosphodiester bond (b) a transfer of high-energy electrons (c) a high-energy thioester bond (d) the heat of molecular collision
C
13-48 In step 4 of the citric acid cycle, the reduction of NAD+ to NADH is coupled to the generation of CO2 and the formation of a high-energy thioester bond. Which molecule provides the sulfhydryl group necessary to form the thioester bond? (a) pyruvate (b) acetyl CoA (c) CoA (d) cysteine side chain in the catalytic pocket
C
13-61 Pyruvate is an important metabolic intermediate that can be converted into several other compounds, depending on which enzyme is catalyzing the reaction. Which of the following cannot be produced from pyruvate in a single enzyme-catalyzed reaction? (a) lactate (b) oxaloacetate (c) citrate (d) alanine
C
13-67 The intermediates of the citric acid cycle are constantly being depleted because they are used to produce many of the amino acids needed to make proteins. The enzyme pyruvate carboxylase converts pyruvate to oxaloacetate to replenish these intermediates. Bacteria, but not animal cells, have additional enzymes that can carry out the reaction acetyl CoA + isocitrate í oxaloacetate + succinate. Which of the following compounds will not support the growth of animal cells when used as the major source of carbon in food, but will support the growth of nonphotosynthetic bacteria? (a) pyruvate (b) glucose (c) fatty acids (d) fructose
C
13-9 Glycolysis generates more stored energy than it expends. What is the net number of activated carrier molecules produced in this process (number and type of molecules produced minus the number of those molecules used as input)? (a) 6 ATP, 2 NADH (b) 4 ATP, 4 NADH (c) 2 ATP, 2 NADH (d) 4 ATP, 2 NADH
C
15-13 Signal sequences that direct proteins to the correct compartment are _________. (a) added to proteins through post-translational modification. (b) added to a protein by a protein translocator. (c) encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination. (d) always removed once a protein is at the correct destination.
C
15-15 Which of the following statements about nuclear transport is true? (a) mRNAs and proteins transit the nucleus through different types of nuclear pores. (b) Nuclear import receptors bind to proteins in the cytosol and bring the proteins to the nuclear pores, where the proteins are released from the receptors into the pores for transit into the nucleus. (c) Nuclear pores have water-filled passages that small, water-soluble molecules can pass through in a nonselective fashion. (d) Nuclear pores are made up of many copies of a single protein.
C
15-18 Your friend works in a biotechnology company and has discovered a drug that blocks the ability of Ran to exchange GDP for GTP. What is the most likely effect of this drug on nuclear transport? (a) Nuclear transport receptors would be unable to bind cargo. (b) Nuclear transport receptors would be unable to enter the nucleus. (c) Nuclear transport receptors would be unable to release their cargo in the nucleus. (d) Nuclear transport receptors would interact irreversibly with the nuclear pore fibrils.
C
15-19 Which of the following statements is true? (a) The signal sequences on mitochondrial proteins are usually at the C-terminus. (b) Most mitochondrial proteins are not imported from the cytosol but are synthesized inside the mitochondria. (c) Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes. (d) Mitochondrial proteins cross the membrane in their native, folded state.
C
15-23 Most proteins destined to enter the endoplasmic reticulum _________. (a) are transported across the membrane after their synthesis is complete. (b) are synthesized on free ribosomes in the cytosol. (c) begin to cross the membrane while still being synthesized. (d) remain within the endoplasmic reticulum.
C
15-25 In which cellular location would you expect to find ribosomes translating mRNAs that encode ribosomal proteins? (a) the nucleus (b) on the rough ER (c) in the cytosol (d) in the lumen of the ER
C
15-29 Which of the following statements is true? (a) Proteins destined for the ER are translated by a special pool of ribosomes whose subunits are always associated with the outer ER membrane. (b) Proteins destined for the ER translocate their associated mRNAs into the ER lumen where they are translated. (c) Proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation. (d) Proteins destined for the ER are translated by a pool of cytosolic ribosomes that contain ER-targeting sequences that interact with ER-associated protein translocators.
C
15-41 Your friend has just joined a lab that studies vesicle budding from the Golgi and has been given a cell line that does not form mature vesicles. He wants to start designing some experiments but wasn't listening carefully when he was told about the molecular defect of this cell line. He's too embarrassed to ask and comes to you for help. He does recall that this cell line forms coated pits but vesicle budding and the removal of coat proteins don't happen. Which of the following proteins might be lacking in this cell line? (a) clathrin (b) Rab (c) dynamin (d) adaptin
C
15-43 Which of the following statements about vesicular membrane fusion is false? (a) Membrane fusion does not always immediately follow vesicle docking. (b) The hydrophilic surfaces of membranes have water molecules associated with them that must be displaced before vesicle fusion can occur. (c) The GTP hydrolysis of the Rab proteins provides the energy for membrane fusion. (d) The interactions of the v-SNAREs and the t-SNAREs pull the vesicle membrane and the target organelle membrane together so that their lipids can intermix.
C
15-48 Cells have oligosaccharides displayed on their cell surface that are important for cell-cell recognition. Your friend discovered a transmembrane glycoprotein, GP1, on a pathogenic yeast cell that is recognized by human immune cells. He decides to purify large amounts of GP1 by expressing it in bacteria. To his purified protein he then adds a branched 14-sugar oligosaccharide to the asparagine of the only Asn-X-Ser sequence found on GP1 (Figure Q15-48). Unfortunately, immune cells do not seem to recognize this synthesized glycoprotein. Which of the following statements is a likely explanation for this problem? (a) The oligosaccharide should have been added to the serine instead of the asparagine. (b) The oligosaccharide should have been added one sugar at a time. (c) The oligosaccharide needs to be further modified before it is mature. (d) The oligosaccharide needs a disulfide bond.
C
15-52 Which of the following statements about the unfolded protein response (UPR) is false? (a) Activation of the UPR results in the production of more ER membrane. (b) Activation of the UPR results in the production of more chaperone proteins. (c) Activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins. (d) Activation of the UPR results in the cytoplasmic activation of gene regulatory proteins.
C
15-54 Vesicles from the ER enter the Golgi at the ______. (a) medial cisternae. (b) trans Golgi network. (c) cis Golgi network. (d) trans cisternae.
C
15-57 Figure Q15-57 shows the orientation of the Krt1 protein on the membrane of a Golgi-derived vesicle that will fuse with the plasma membrane. Given this diagram, which of the following statements is true? (a) When this vesicle fuses with the plasma membrane, the entire Krt1 protein will be secreted into the extracellular space. (b) When this vesicle fuses with the plasma membrane, the C-terminus of Krt1 will be inserted into the plasma membrane. (c) When this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be in the extracellular space. (d) When this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be cytoplasmic.
C
15-6 Which of the following organelles is not part of the endomembrane system? (a) Golgi apparatus (b) the nucleus (c) mitochondria (d) lysosomes
C
17-15 You are studying nuclear lamins in yeast. Using recombinant DNA technology, you alter the coding sequence of a nuclear lamin gene such that the gene now codes for a nuclear lamin protein that can no longer be phosphorylated when the nuclear envelope is broken down during mitosis. What do you predict would happen if the yeast cell only had the altered nuclear lamin gene (and not the unaltered version)? (a) Mitosis should proceed as usual because the dephosphorylation of the lamin is what is important for nuclear lamina assembly during mitosis, so phosphorylation will not be necessary. (b) Disassembly of the nuclear lamins will occur prematurely because the lamins cannot be phosphorylated. (c) Nuclear lamins will no longer disassemble properly during mitosis. (d) Nuclear lamins will be unable to produce dimers, as coiled-coil formation will be disrupted.
C
17-2 Which of the following statements about the cytoskeleton is false? (a) The cytoskeleton is made up of three types of protein filaments. (b) The cytoskeleton controls the location of organelles in eukaryotic cells. (c) Covalent bonds between protein monomers hold together cytoskeletal filaments. (d) The cytoskeleton of a cell can change in response to the environment.
C
17-24 The microtubules in a cell form a structural framework that can have all the following functions except which one? (a) holding internal organelles such as the Golgi apparatus in particular positions in the cell (b) creating long, thin cytoplasmic extensions that protrude from one side of the cell (c) strengthening the plasma membrane (d) moving materials from one place to another inside a cell
C
17-35 Which of the following statements is correct? Kinesins and dyneins ____________________. (a) have tails that bind to the filaments. (b) move along both microtubules and actin filaments. (c) often move in opposite directions to each other. (d) derive their energy from GTP hydrolysis.
C
17-40 Figure Q17-40A shows how the movement of dynein causes the flagellum to bend. If instead of the normal situation, the polarity of the adjacent doublet of microtubules were to be reversed (see Figure Q17-40B), what do you predict would happen?(a) No bending would occur. (b) Bending would occur exactly as diagrammed in Figure Q17-40A. (c) Bending would occur, except that the right microtubule doublet would move down relative to the left one. (d) The two microtubule doublets would slide away from each other.
C
17-52 Figure Q17-52 shows the leading edge of a lamellipodium. Which of the following statements is false?(a) Nucleation of new filaments near the leading edge pushes the plasma membrane forward. (b) ARP proteins nucleate the branched actin filaments in the lamellipodium. (c) Capping proteins bind to the minus end of actin filaments. (d) There is more ATP-bound actin at the leading edge than in the actin filaments away from the leading edge.
C
17-53 You are examining a cell line in which activation of the Rho family member Rac promotes lamellipodia formation. Which of the following statements is most likely to be true? (a) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more unbranched actin filaments than normal cells. (b) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more unbranched actin filaments than normal cells. (c) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells. (d) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more branched actin filaments than normal cells.
C
17-56 Which of the following structures shorten during muscle contraction? (a) myosin filaments (b) flagella (c) sarcomeres (d) actin filaments
C
13-14 Several different classes of enzymes are needed for the catabolism of carbohydrates. Which of the following descriptions best matches the function of a kinase? (a) An enzyme that catalyzes the rearrangement of bonds within a single molecule. (b) An enzyme that catalyzes a change in the position of a specific chemical group within a single molecule. (c) An enzyme that catalyzes the oxidation of a molecule by removing a hydride ion. (d) An enzyme that catalyzes the addition of phosphate groups to other molecules.
D
13-18 On a diet consisting of nothing but protein, which of the following is the most likely outcome? (a) loss of weight because amino acids cannot be used for the synthesis of fat (b) muscle gain because the amino acids will go directly into building muscle (c) tiredness because amino acids cannot be used to generate energy (d) excretion of more nitrogenous (ammonia-derived) wastes than with a more balanced diet
D
13-21 Which of the following processes do not take place in the mitochondria? (a) citric acid cycle (b) conversion of pyruvate to activated acetyl groups (c) oxidation of fatty acids to acetyl CoA (d) glycogen breakdown
D
13-3 Which of the following stages in the breakdown of the piece of toast you had for breakfast generates the most ATP? (a) the digestion of starch to glucose (b) glycolysis (c) the citric acid cycle (d) oxidative phosphorylation
D
13-34 Pyruvate must move from the cytosol into the mitochondria, where it is oxidized to form CO2 and acetyl CoA by the pyruvate dehydrogenase complex. How many different enzymes and what total number of polypeptides, respectively, are required to perform this oxidation process in the mitochondrion?(a) 1; 60 (b) 3; 3 (c) 3; 26 (d) 3; 60
D
13-43 The citric acid cycle is a series of oxidation reactions that removes carbon atoms from substrates in the form of CO2. Once a molecule of acetyl CoA enters the citric acid cycle, how many complete cycles are required for both of the carbon atoms in its acetyl groupto be oxidized to CO2? (a) 1 (b) 2 (c) 3 (d) 4
D
13-46 In step 2 of the citric acid cycle, the enzyme aconitase generates isocitrate from citrate. Which of the following statements about this reaction is true? (a) There is a substantial free-energy difference between the reactants and products of this reaction. (b) The unbonded electrons from hydroxide ions provide energy for this reaction. (c) The aconitase enzyme functions as a mutase in this reaction. (d) The reaction sequence first generates one molecule of water and then consumes one molecule of water.
D
13-47 In step 3 of the citric acid cycle, the oxidation of isocitrate and the production of CO2 are coupled to the reduction of NAD+, generating NADH and an α-ketoglutarate molecule. In the isocitrate molecule shown in Figure Q13-47, which carbon is lost as CO2 and which is converted to a carbonyl carbon? (a) 4 and 6 (b) 6 and 5 (c) 5 and 4 (d) 6 and 4
D
13-55 The oxygen-dependent reactions required for cellular respiration were originally thought to occur in a linear pathway. By using a competitive inhibitor for one enzyme in the pathway, investigators discovered that these reactions occur in a cycle. Which enzyme was inhibited? (a) aconitase (b) isocitrate dehydrogenase (c) malate dehydrogenase (d) succinate dehydrogenase
D
13-64 Step 3 in glycolysis requires the activity of phosphofructokinase to convert fructose 6-phosphate into fructose 1,6-bisphosphate. Which of the following molecules is an allosteric inhibitor of this enzyme? (a) Pi (b) AMP (c) ADP (d) ATP
D
13-65 The conversion of fructose 1,6-bisphosphate to fructose 6-phosphate is catalyzed by a fructose 1,6-bisphosphatase and is one of the final steps in gluconeogenesis. Which of the following molecules is an allosteric activator of this enzyme? (a) Pi (b) AMP (c) ADP (d) ATP
D
13-68 Pyruvate can be converted into many other molecules by various biosynthetic and metabolic pathways, which makes it a central hub in the regulation of cellular metabolism. Which of the following molecules is not made from pyruvate? (a) oxaloacetate (b) ethanol (c) lactate (d) NADH
D
15-10 Where are proteins in the chloroplast synthesized? (a) in the cytosol (b) in the chloroplast (c) on the endoplasmic reticulum (d) in both the cytosol and the chloroplast
D
15-11 Proteins that are fully translated in the cytosol do not end up in _______. (a) the cytosol. (b) the mitochondria. (c) the interior of the nucleus. (d) transport vesicles.
D
15-24 After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify the RNAs attached to it. Which of the following proteins do you expect the RNA from the rough endoplasmic reticulum to encode? (a) soluble secreted proteins (b) ER membrane proteins (c) plasma membrane proteins (d) all of the above
D
15-27 You are interested in Fuzzy, a soluble protein that functions within the ER lumen. Given that information, which of the following statements must be true? (a) Fuzzy has a C-terminal signal sequence that binds to SRP. (b) Only one ribosome can be bound to the mRNA encoding Fuzzy during translation. (c) Fuzzy must contain a hydrophobic stop-transfer sequence. (d) Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be ejected into the ER membrane and degraded.
D
15-28 Which of the following statements about a protein in the lumen of the ER is false? (a) A protein in the lumen of the ER is synthesized by ribosomes on the ER membrane. (b) Some of the proteins in the lumen of the ER can end up in the extracellular space. (c) Some of the proteins in the lumen of the ER can end up in the lumen of an organelle in the endomembrane system. (d) Some of the proteins in the lumen of the ER can end up in the plasma membrane.
D
15-36 Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels? (a) lysosome í endosome í plasma membrane (b) ER í lysosome í plasma membrane (c) Golgi í lysosome í plasma membrane (d) ER í Golgi í plasma membrane
D
15-40 Which of the following protein families are not involved in directing transport vesicles to the target membrane? (a) SNAREs (b) Rabs (c) tethering proteins (d) adaptins
D
15-45 N-linked oligosaccharides on secreted glycoproteins are attached to (a) nitrogen atoms in the polypeptide backbone. (b) the serine or threonine in the sequence Asn-X-Ser/Thr. (c) the N-terminus of the protein. (d) the asparagine in the sequence Asn-X-Ser/Thr.
D
15-47 Which of the following statements about disulfide bond formation is false? (a) Disulfide bonds do not form under reducing environments. (b) Disulfide bonding occurs by the oxidation of pairs of cysteine side chains on the protein. (c) Disulfide bonding stabilizes the structure of proteins. (d) Disulfide bonds form spontaneously within the ER because the lumen of the ER is oxidizing.
D
15-49 Different glycoproteins can have a diverse array of oligosaccharides. Which of the statements below about this diversity is true? (a) Extensive modification of oligosaccharides occurs in the extracellular space. (b) Different oligosaccharides are covalently linked to proteins in the ER and the Golgi. (c) A diversity of oligosaccharyl transferases recognizes specific protein sequences, resulting in the linkage of a variety of oligosaccharides to proteins. (d) Oligosaccharide diversity comes from modifications that occur in the ER and the Golgi of the 14-sugar oligosaccharide added to the protein in the ER.
D
17-13 Keratins, neurofilaments, and vimentins are all categories of intermediate filaments. Which of the following properties is not true of these types of intermediate filaments? (a) They strengthen cells against mechanical stress. (b) Dimers associate by noncovalent bonding to form a tetramer. (c) They are found in the cytoplasm. (d) Phosphorylation causes disassembly during every mitotic cycle.
D
17-16 You are interested in understanding the regulation of nuclear lamina assembly. To create an in vitro system for studying this process you start with partly purified nuclear lamina subunits to which you will add back purified cellular components to drive nuclear lamina assembly. Before you start doing experiments, your instructor suggests that you consider what type of conditions would be most amenable to the assembly of the nuclear lamina from its individual subunits in vitro. Which of the following conditions do you predict would be most likely to enhance the assembly of the nuclear lamina? (a) addition of phosphatase inhibitors (b) addition of ATP (c) addition of a concentrated salt solution that is 10 times the concentration normally found in the nucleoplasm (d) addition of protein kinase inhibitors
D
17-19 Which of the following statements about the structure of microtubules is false? (a) Microtubules are built from protofilaments that come together to make a hollow structure. (b) The two ends of a protofilament are chemically distinct, with α-tubulin exposed at one end and β-tubulin exposed at the other end. (c) Within a microtubule, all protofilaments are arranged in the same orientation, giving the microtubule structural polarity. (d) α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.
D
17-23 The hydrolysis of GTP to GDP carried out by tubulin molecules ________________. (a) provides the energy needed for tubulin to polymerize. (b) occurs because the pool of free GDP has run out. (c) tips the balance in favor of microtubule assembly. (d) allows the behavior of microtubules called dynamic instability.
D
17-28 Which of the following statements regarding dynamic instability is false? (a) Each microtubule filament grows and shrinks independently of its neighbors. (b) The GTP cap helps protect a growing microtubule from depolymerization. (c) GTP hydrolysis by the tubulin dimer promotes microtubule shrinking. (d) The newly freed tubulin dimers from a shrinking microtubule can be immediately captured by growing microtubules and added to their plus end.
D
17-33 Microtubules are important for transporting cargo in nerve cell axons, as diagrammed in Figure Q17-33. Notice that the two types of cargo are traveling in opposite directions. Which of the following statements is likely to be false? (a) The gray cargo is attached to dynein. (b) The black cargo and the gray cargo require ATP hydrolysis for their motion. (c) The black cargo moving toward the axon terminal contains a domain that specifically interacts with the tail domain of a particular kind of motor. (d) The black cargo and the gray cargo are moving along microtubules of opposite polarity.
D
17-4 Which of the following statements about the cytoskeleton is true? (a) All eukaryotic cells have actin, microtubules, and intermediate filaments in their cytoplasm. (b) The cytoskeleton provides a rigid and unchangeable structure important for the shape of the cell. (c) The three cytoskeletal filaments perform distinct tasks in the cell and act completely independently of one another. (d) Actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end.
D
17-42 Which of the following statements about actin is false? (a) ATP hydrolysis decreases actin filament stability. (b) Actin at the cell cortex helps govern the shape of the plasma membrane. (c) Actin filaments are nucleated at the side of existing actin filaments in lamellipodia. (d) The dynamic instability of actin filaments is important for cell movement.
D
17-45 For both actin and microtubule polymerization, nucleotide hydrolysis is important for ______. (a) stabilizing the filaments once they are formed. (b) increasing the rate at which subunits are added to the filaments. (c) promoting nucleation of filaments. (d) decreasing the binding strength between subunits on filaments.
D
17-50 Cell movement involves the coordination of many events in the cell. Which of the following phenomena is not required for cell motility? (a) Myosin-mediated contraction at the rear of the moving cell. (b) Integrin association with the extracellular environment. (c) Nucleation of new actin filaments. (d) Release of Ca2+ from the sarcoplasmic reticulum.
D
17-55 Your friend works in a biotech company that has just discovered a drug that seems to promote lamellipodia formation in cells. Which of the following molecules is unlikely to be involved in the pathway that this drug affects? (a) Rac (b) ARP (c) actin (d) myosin
D
17-6 Which of the statements below about intermediate filaments is false? (a) They can stay intact in cells treated with concentrated salt solutions. (b) They can be found in the cytoplasm and the nucleus. (c) They can be anchored to the plasma membrane at a cell-cell junction. (d) Each filament is about 10 μm in diameter.
D
17-63 Consider the in vitro motility assay using purified kinesin and purified polymerized microtubules shown in Figure Q17-63. The three panels are images taken at 1-second intervals. In this figure, three microtubules have been numbered to make it easy to identify them. Which of the following statements about this assay is false? (a) Kinesin molecules are attached by their tails to a glass slide. (b) The microtubules used in this assay must be polymerized using conditions that stabilize tubule formation or else they would undergo dynamic instability. (c) ATP must be added for this assay to work. (d) Addition of the nonhydrolyzable ATP analog (AMP-PNP) would cause the microtubules to move faster
D