Cell Biology Exam 4

1. The overall relationship that links bond-forming reactions to membrane transport processes in the mitochondria is called a. Chemiosmotic coupling. b. proton pumping. c. electron transfer. d. ATP synthesis.

a

11. 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

11. 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

12. What is the source of protons that are pumped out of the mitochondrial matrix in Stage 1 of oxidative phosphorylation? a. NADH b. H2O c. FADH d. H2S

a

12. 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

13. Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly. The activated receptor stimulates a G protein, which opens a K+ channel in the plasma membrane, as shown in Figure 16-13. Which of the following would enhance this effect of the acetylcholine? a. addition of a high concentration of a nonhydrolyzable analog of GTP b. addition of a drug that prevents the α subunit from exchanging GDP for GTP c. mutations in the acetylcholine receptor that weaken the interaction between the receptor and acetylcholine d. mutations in the acetylcholine receptor that weaken the interaction between the receptor and the G protein

a

13. 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.

a

15. 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 contain enzymes that help inactivate toxins. d. Proteins do not need to unfold to enter the peroxisome.

a

17. Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the vicinity of the active PKC. Figure 16-17 shows how G proteins can indirectly activate PKC. You have discovered the enzyme activated by PKC that mediates the lipid modification. You call the enzyme Rafty and demonstrate that activated PKC directly phosphorylates Rafty, activating it to modify the plasma membrane lipids in the vicinity of the cell where PKC is active; these lipid modifications can be detected by dyes that bind to the modified lipids. Cells lacking Rafty do not have these modifications, even when PKC is active. Which of the following conditions would lead to signal-independent modification of the membrane lipids by Rafty? a. the expression of a constitutively active phospholipase C b. a mutation in the GPCR that binds the signal more tightly c. a Ca2+ channel in the endoplasmic reticulum with an increased affinity for IP3 d. a mutation in the gene that encodes Rafty such that the enzyme can no longer be phosphorylated by PKC

a

17. 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

18. The graph in Figure 17-18 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. Figure 17-18 Three parts of the curve are labeled above it as A, B, and C. You conduct a similar in vitro tubulin-polymerization experiment, only this time 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 17-18? 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

18. You are interested in cell-size regulation and discover that signaling through a GPCR called ERC1 is important in controlling cell size in embryonic rat cells. The G protein downstream of ERC1 activates adenylyl cyclase, which ultimately leads to the activation of PKA. You discover that cells that lack ERC1 are 15% smaller than normal cells, while cells that express a mutant, constitutively activated version of PKA are 15% larger than normal cells. Given these results, which of the following treatments to embryonic rat cells should lead to smaller cells? a. addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive b. addition of a drug that prevents GTP hydrolysis by Gα c. addition of a drug that activates adenylyl cyclase d. addition of a drug that mimics the ligand of ERC1

a

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

21. The relationship of free-energy change (ΔG) to the concentrations of reactants and products is important because it predicts the direction of spontaneous chemical reactions. In the hydrolysis of ATP to ADP and inorganic phosphate (Pi), the standard free-energy change (ΔG°) is −7.3 kcal/mole. The free-energy change depends on concentrations according to the following equation: ΔG = ΔG° + 1.42 log10 ([ADP] [Pi]/[ATP]) In a resting muscle, the concentrations of ATP, ADP, and Pi are approximately 0.005 M, 0.001 M, and 0.010 M, respectively. What is the ΔG for ATP hydrolysis in resting muscle? a. −11.1 kcal/mole b. −8.72 kcal/mole c. 6.01 kcal/mole d. −5.88 kcal/mole

a

23. Which of the following items is not important for flagellar movement? a. sarcoplasmic reticulum b. ATP c. dynein d. microtubules

a

24. Which of the following mechanisms is NOT directly involved in inactivating an activated RTK? a. dephosphorylation by serine/threonine phosphatases b. dephosphorylation by protein tyrosine phosphatases c. removal of the RTK from the plasma membrane by endocytosis d. digestion of the RTK in lysosomes

a

24. 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

27. Which ratio of NADH to NAD+ in solution will generate the largest positive redox potential? a. 1:10 b. 10:1 c. 1:1 d. 5:1

a

28. 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 the addition of monomers binding nonhydrolyzable ATP would not affect actin filament length.

a

3. Which of the following statements describes the phosphorylation event that occurs during the process known as "oxidative phosphorylation"? a. A phosphate group is added to ADP. b. ATP is hydrolyzed in order to add phosphate groups to protein substrates. c. A phosphate group is added to molecular oxygen. d. Inorganic phosphate is transported into the mitochondrial matrix, increasing the local phosphate concentration.

a

33. The ethylene response in plants involves a dimeric transmembrane receptor. When the receptor is not bound to ethylene, the receptor binds to and activates a protein kinase, which activates an intracellular signaling pathway that leads to the degradation of a transcriptional regulator important for transcribing the ethylene-responsive genes (see Figure 16-33). You discover a phosphatase that is important for ethylene signaling, and you name it PtpE. Plants lacking PtpE never turn on ethylene-responsive genes, even in the presence of ethylene. You find that PtpE dephosphorylates serine 121 on the transcriptional regulator. Furthermore, plants lacking PtpE degrade the transcriptional regulator in the presence of ethylene. Which of the following statements is inconsistent with your data? a. When the transcriptional regulator is phosphorylated, it activates transcription of the ethylene-responsive genes. b. When the transcriptional regulator is not phosphorylated, it binds to DNA. c. Activation of the protein kinase that binds to the ethylene receptor leads to inactivation of PtpE. d. Binding of ethylene to its receptor leads to the activation of PtpE.

a

35. When Ras is activated, cells will divide. A dominant-negative form of Ras clings too tightly to GDP. You introduce a dominant-negative form of Ras into cells that also have a normal version of Ras. Which of the following statements is TRUE? a. The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras. b. The cells you create will run out of the GTP necessary to activate Ras. c. The cells you create will divide more frequently compared to normal cells in response to the extracellular signals that typically activate Ras. d. The normal Ras in the cells you create will not be able to bind GDP because the dominant-negative Ras binds to GDP too tightly.

a

36. In stage 1 of photosynthesis, a proton gradient is generated and ATP is synthesized. Where do protons become concentrated in the chloroplast? a. thylakoid space b. stroma c. inner membrane d. thylakoid membrane

a

37. 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

38. 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

4. 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

4. Modern eukaryotes depend on mitochondria to generate most of the cell's ATP. How many molecules of ATP can a single molecule of glucose generate? a. 30 b. 2 c. 20 d. 36

a

6. Which of the following statements describes the mitochondrial outer membrane? a. It is permeable to molecules with molecular mass as high as 5000 daltons. b. It contains transporters for ATP molecules. c. It contains proteins that are released during apoptosis. d. It contains enzymes required for the oxidation of fatty acids.

a

6. Which of the following statements is TRUE? a. Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior. b. To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol. c. A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response. d. Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type.

a

7. Proteins that are fully translated in the cytosol and lack a sorting signal will end up in the a. cytosol. b. mitochondria. c. interior of the nucleus. d. nuclear membrane.

a

7. Which of the following statements about molecular switches is FALSE? a. Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. b. Protein kinases transfer the terminal phosphate from ATP onto a protein. c. Serine/threonine kinases are the most common types of protein kinase. d. A GTP-binding protein exchanges its bound GDP for GTP to become activated.

a

9. 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

1. When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a a. neurotransmitter. b. hormone. c. dissolved gas. d. scaffold.

b

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 the smooth ER. c. Steroid hormones are synthesized on the smooth ER. d. The ER membrane is contiguous with the outer nuclear membrane.

b

10. NADH contains a high-energy bond that, when cleaved, donates a pair of electrons to the electron-transport chain. What are the immediate products of this bond cleavage? a. NAD+ + OH− b. NAD+ + H− c. NAD− + H+ d. NAD + H

b

14. During the mating process, yeast cells respond to pheromones secreted by other yeast cells. These pheromones bind GPCRs on the surface of the responding cell and lead to the activation of G proteins inside the cell. When a wild-type yeast cell senses the pheromone, its physiology changes in preparation for mating: the cell stops growing until it finds a mating partner. If yeast cells do not undergo the appropriate response after sensing a pheromone, they are considered sterile. Yeast cells that are defective in one or more components of the G protein have characteristic phenotypes in the absence and presence of the pheromone, which are listed in Table 16-14. Which of the following models is consistent with the data from the analysis of these mutants? Explain your answer. a. The α subunit activates the mating response but is inhibited when bound to βγ. b. The βγ subunit activates the mating response but is inhibited when bound to α. c. The G protein is inactive; either the free α or free βγ complex is capable of activating the mating response. d. The G protein is active; both free α and free βγ complex are required to inhibit the mating response.

b

14. Osmosis describes the movement of water across a biological membrane and down its concentration gradient. In chemiosmosis, useful energy is harnessed by the cell from the movement of __________ across the inner mitochondrial membrane into the matrix __________ a concentration gradient. a. ATP, against b. protons, down c. electrons, down d. ADP, against

b

14. 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. Which of the following components of the electron-transport chain does NOT act as a proton pump? a. NADH dehydrogenase b. cytochrome c c. cytochrome c reductase d. cytochrome c oxidase

b

15. 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 that MtA a. is involved in stabilizing microtubules. b. binds to GTP-bound tubulin on microtubules. c. is important for the interaction of microtubules with the centrosome. d. will not bind to purified microtubules in a test tube.

b

18. 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

b

18. Which of the following statements is TRUE? a. The NADH dehydrogenase complex does not pump protons across the membrane. b. The pH in the mitochondrial matrix is higher than the pH in the intermembrane space. c. The proton concentration gradient and the membrane potential across the inner mitochondrial membrane tend to work against each other in driving protons from the intermembrane space into the matrix. d. The difference in proton concentration across the inner mitochondrial membrane has a much larger effect than the membrane potential on the total proton-motive force.

b

19. The mitochondrial ATP synthase consists of several different protein subunits. Which subunit binds to ADP + Pi and catalyzes the synthesis of ATP as a result of a conformational change? a. transmembrane H+ carrier b. F1 ATPase head c. peripheral stalk d. central stalk

b

19. 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

20. Figure 16-20 shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine? a. a smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO b. a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP c. a muscle cell that has cyclic GMP phosphodiesterase constitutively active d. a drug that blocks an enzyme involved in the metabolic pathway from arginine to NO

b

22. Figure 15-22 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? Figure 15-22 a. The N-terminus of this protein is cytoplasmic. b. The C-terminus of this protein is cytoplasmic. c. The mature version of this protein will span the membrane twice, with both the N- and C- terminus in the cytoplasm. d. none of these answers are correct.

b

22. The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration would be most likely to prevent receptor dimerization? a. a mutation that increases the affinity of RGFR for RGF b. a mutation that prevents RGFR from binding to RGF c. changing the tyrosines that are normally phosphorylated on RGFR dimerization to alanines d. changing the tyrosines that are normally phosphorylated on RGFR dimerization to glutamic acid

b

25. Molecules to be packaged into vesicles for transport are selected by a. clathrin. b. adaptins. c. dynamin. d. SNAREs.

b

25. Which of the following statements about "redox potential" is TRUE? a. Redox potential is a measure of a molecule's capacity to strip electrons from oxygen. b. For molecules that have a strong tendency to pass along their electrons, the standard redox potential is negative. c. The transfer of electrons from cytochrome c oxidase to oxygen has a negative redox potential. d. A molecule's redox potential is a measure of the molecule's capacity to pass along electrons to oxygen.

b

25. You are interested in further understanding the signal transduction pathway that controls the production of Pig1, a protein important for regulating cell size. Activation of the TRK receptor leads to activation of the GTP-binding protein, Ras, which then activates a protein kinase that phosphorylates the SZE transcription factor. SZE only interacts with the nuclear transport receptor when it is phosphorylated. SZE is a gene activator for the Pig1 gene. This pathway is diagrammed in Figure 16-25. Normal cells grown under standard conditions (without ligand) are 14 μm in diameter while normal cells exposed to TRK ligand are 10.5 μm in diameter. Given this situation, which of the following conditions do you predict will more likely lead to smaller cells? a. addition of TRK ligand and a drug that stimulates the GTPase activity of Ras b. addition of TRK ligand and a drug that inhibits the activity of the phosphatase that acts on SZE c. addition of TRK ligand and a drug that stimulates the degradation of Pig1 d. addition of TRK ligand and a drug that inhibits Pig1 binding to DNA

b

26. 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

26. Which of the following statements is TRUE? a. MAP kinase is important for phosphorylating MAP kinase kinase. b. PI 3-kinase phosphorylates a lipid in the plasma membrane. c. Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP. d. Dimerization of GPCRs leads to Gα activation.

b

27. The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to a. activate the RTK. b. create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane. c. directly phosphorylate Akt. d. create DAG.

b

28. An 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

28. Ubiquinone is one of two mobile electron carriers in the electron-transport chain. Where does the additional pair of electrons reside in the reduced ubiquinone molecule? a. The electrons are added directly to the aromatic ring. b. The electrons are added to each of two ketone oxygens on the aromatic ring. c. The electrons are added to the hydrocarbon tail, which hides them inside the membrane bilayer. d. Both electrons, and one proton, are added to a single ketone oxygen bound to the aromatic ring.

b

29. Which of the following reactions has a sufficiently large free-energy change to enable it to be used, in principle, to provide the energy needed to synthesize one molecule of ATP from ADP and Pi under standard conditions? See Table 14-29. Recall that ΔG° = —n (0.023) ΔE0′, and ΔE0′ = E0′ (acceptor) − E0′ (donor). a. the reduction of a molecule of pyruvate by NADH b. the reduction of a molecule of cytochrome b by NADH c. the reduction of a molecule of cytochrome b by reduced ubiquinone d. the oxidation of a molecule of reduced ubiquinone by cytochrome c

b

29. Which of the following statements is FALSE? a. Formins promote the formation of unbranched actin filaments. 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

3. Which of the following statements is TRUE? a. Because endocrine signals are broadcast throughout the body, all cells will respond to the hormonal signal. b. The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling. c. Paracrine signaling involves the secretion of signals into the bloodstream for distribution throughout the organism. d. The axons of neurons typically signal target cells using membrane-bound signaling molecules that act on receptors in the target cells.

b

30. Cytochrome c oxidase is an enzyme complex that uses metal ions to help coordinate the transfer of four electrons to O2. Which metal atoms are found in the active site of this complex? a. two iron atoms b. one iron atom and one copper atom c. one iron atom and one zinc atom d. one zinc atom and one copper atom

b

32. The last common ancestor to plants and animals was a unicellular eukaryote. Thus, it is thought that multicellularity and the attendant demands for cell communication arose independently in these two lineages. This evolutionary viewpoint accounts nicely for the vastly different mechanisms that plants and animals use for cell communication. Fungi use signaling mechanisms and components that are very similar to those used in animals. Which of the phylogenetic trees shown in Figure 16-32 does this observation support?

b

34. 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

35. 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

23. A protein kinase can act as an integrating device in signaling if it a. phosphorylates more than one substrate. b. catalyzes its own phosphorylation. c. is activated by two or more proteins in different signaling pathways. d. initiates a phosphorylation cascade involving two or more protein kinases.

c

36. 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

39. In the electron-transport chain in chloroplasts, __________-energy electrons are taken from __________. a. high; H2O. b. low; H2O. c. high; NADPH. d. low; NADPH.

b

4. 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

40. The photosystems in chloroplasts contain hundreds of chlorophyll molecules, most of which are part of a. plastoquinone. b. the antenna complex. c. the reaction center. d. the ferredoxin complex.

b

40. 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

41. If you shine light on chloroplasts and measure the rate of photosynthesis as a function of light intensity, you get a curve that reaches a plateau at a fixed rate of photosynthesis, x, as shown in Figure 14-41. Which of the following conditions will increase the value of x? a. increasing the number of chlorophyll molecules in the antenna complexes b. increasing the number of reaction centers c. adding a powerful oxidizing agent d. decreasing the wavelength of light used

b

5. Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which of the following statements is FALSE? a. Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract. b. Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family. c. Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways. d. Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal.

b

5. Intermediate filaments help protect animal cells from mechanical stress because filaments a. 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. in each cell are indirectly connected to the filaments of a neighboring cell through the desmosome, creating a continuous mechanical link between cells. c. remain independent of other cytoskeletal elements and keep the mechanical stress away from other cellular components. d. 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

6. Intermediate filaments are made from elongated fibrous proteins that are assembled into a ropelike structure. Figure 17-6 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? Figure 17-6 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

7. Which of the following statements describes the mitochondrial inner membrane? a. It is permeable to molecules with molecular mass as high as 5000 daltons. b. It contains transporters for ATP molecules. c. It contains proteins that are released during apoptosis. d. It contains enzymes required for the oxidation of fatty acids.

b

9. Cell lines A and B both survive in tissue culture containing serum but do not proliferate. Factor F is known to stimulate proliferation in cell line A. Cell line A produces a receptor protein (R) that cell line B does not produce. To test the role of receptor R, you introduce this receptor protein into cell line B, using recombinant DNA techniques. You then test all of your various cell lines in the presence of serum for their response to factor F, with the results summarized in Table 16-9. Which of the following cannot be concluded from your results above? a. Binding of factor F to its receptor is required for proliferation of cell line A. b. Receptor R binds to factor F to induce cell proliferation in cell line A. c. Cell line A expresses a receptor for factor F. d. Factor F is not required for proliferation in cell line B.

b

34. Which of the following structures shorten during muscle contraction? a. myosin filaments b. flagella c. sarcomeres d. actin filaments

c

39. Which of the following drugs is toxic for our cells? A. Phalloidin, which binds along actin filaments and stabilizes them. B. Nocodazole, which binds to tubulin subunits and prevents microtubule polymerization. C. Colchicine, which caps microtubule ends and leads to their depolymerization. D. All of the above.

d

1. 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

10. The following happens when a G-protein-coupled receptor activates a G protein. a. The β subunit exchanges its bound GDP for GTP. b. The GDP bound to the α subunit is phosphorylated to form bound GTP. c. The α subunit exchanges its bound GDP for GTP. d. It activates the α subunit and inactivates the βγ complex.

c

10. 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 contain proteins with disordered segments that fill the channel and allow small water-soluble molecules to pass through in a non-selective fashion. ? maybe d. Nuclear pores are made up of many copies of a single protein.

c

12. 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

13. What is the final result of the electron transfers in Stage 1 of the membrane-based processes that drive ATP synthesis in mitochondria? a. OH− is oxidized to O2 b. pyruvate is oxidized to CO2 c. O2 is reduced to H2O d. H− is converted to H2

c

14. 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

15. You are interested in how cyclic-AMP-dependent protein kinase A (PKA) functions to affect learning and memory, and you decide to study its function in the brain. It is known that, in the cells you are studying, PKA works via a signal transduction pathway like the one depicted in Figure 16-15. Furthermore, it is also known that activated PKA phosphorylates the transcriptional regulator called Nerd that then activates transcription of the gene Brainy. Which situation described below will lead to an increase in Brainy transcription? a. a mutation in the Nerd gene that produces a protein that cannot be phosphorylated by PKA b. a mutation in the nuclear import sequence of PKA from PPKKKRKV to PPAAAAAV c. a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive d. a mutation in the gene that encodes adenylyl cyclase that renders the enzyme unable to interact with the α subunit of the G protein

c

16. Most proteins destined to enter the endoplasmic reticulum a. are transported across the membrane after their synthesis is complete. b. are completely translated on free ribosomes in the cytosol. c. begin to cross the membrane while still being synthesized. d. remain within the endoplasmic reticulum.

c

17. During Stage 2 of oxidative phosphorylation, ATP synthesis is powered by movement of __________ ions through the __________. a. H+; H+ pump b. OH-; porin complex c. H+; ATP synthase d. elections; electron-transport chain

c

19. The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by a. activating a G protein. b. activating a receptor tyrosine kinase. c. diffusing into cells and stimulating the cyclase directly. d. activating an intracellular protein kinase.

c

20. Bongkrekic acid is an antibiotic that inhibits the ATP/ADP transport protein in the inner mitochondrial membrane. Which of the following will allow electron transport to occur in mitochondria treated with bongkrekic acid? a. placing the mitochondria in anaerobic conditions b. adding FADH2 c. making the inner membrane permeable to protons d. inhibiting the ATP synthase

c

21. 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

21. The growth factor Superchick stimulates the proliferation of cultured chicken cells. The receptor that binds Superchick is a receptor tyrosine kinase (RTK), and many chicken tumor cell lines have mutations in the gene that encodes this receptor. Which of the following types of mutation would be expected to promote uncontrolled cell proliferation? a. a mutation that prevents dimerization of the receptor b. a mutation that destroys the kinase activity of the receptor c. a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor d. a mutation that prevents the binding of the normal extracellular signal to the receptor

c

21. 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

23. The relationship of free-energy change (ΔG) to the concentrations of reactants and products is important because it predicts the direction of spontaneous chemical reactions. Consider, for example, the hydrolysis of ATP to ADP and inorganic phosphate (Pi). The standard free- energy change (ΔG°) for this reaction is −7.3 kcal/mole. The free-energy change depends on concentrations according to the following equation: ΔG = ΔG° + 1.42 log10 ([ADP] [Pi]/[ATP]) In a resting muscle, the concentrations of ATP, ADP, and Pi are approximately 0.005 M, 0.001 M, and 0.010 M, respectively. At [Pi] = 0.010 M, what will be the ratio of [ATP] to [ADP] at equilibrium? a. 1.38 × 106 b. 1 c. 7.2 × 10−8 d. 5.14

c

24. Figure 17-24A 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 17-24B), what do you predict would happen? Figure 17-24 a. No bending would occur. b. Bending would occur exactly as diagrammed in Figure 17-24A. 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

24. NADH and FADH2 carry high-energy electrons that are used to power the production of ATP in the mitochondria. These cofactors are generated during glycolysis, the citric acid cycle, and the fatty acid oxidation cycle. Which molecule below can produce the most ATP? Explain your answer. a. NADH from glycolysis b. FADH2 from the fatty acid cycle c. NADH from the citric acid cycle d. FADH2 from the citric acid cycle

c

26. 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

c

26. Which of the following statements is TRUE? a. Only compounds with negative redox potentials can donate electrons to other compounds under standard conditions. b. Compounds that donate one electron have higher redox potentials than those compounds that donate two electrons. c. The ΔE0′ of a redox pair does not depend on the concentration of each member of the pair. d. The free-energy change, ΔG, for an electron-transfer reaction does not depend on the concentration of each member of a redox pair.

c

27. 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 was not listening carefully when he was told about the molecular defect of this cell line. He is 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

29. 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

3. Which of the following organelles is not part of the endomembrane system? a. Golgi apparatus b. the endosome c. mitochondria d. lysosomes

c

31. Figure 17-31 shows the leading edge of a lamellipodium. Which of the following statements is FALSE? Figure 17-31 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

32. 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 15-32). 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

32. Which of the following is not an electron carrier that participates in the electron-transport chain? a. cytochrome b. quinone c. rhodopsin d. copper ion

c

32. 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

33. Which of the following statements about cytochrome c is TRUE? a. Cytochrome c shuttles electrons between the NADH dehydrogenase complex and cytochrome c reductase complex. b. When cytochrome c becomes reduced, two cysteines (sulfur-containing amino acids) become covalently bound to a heme group. c. The pair of electrons accepted by cytochrome c are added to the porphyrin ring of the bound heme group. d. Cytochrome c is the last protein in the electron-transport chain, passing its electrons directly to molecular oxygen, a process that reduces O2 to H2O.

c

34. Figure 16-34 shows that intracellular signaling pathways can be highly interconnected. From the information in Figure 16-34, which of the following statements is FALSE? a. The GPCR and the RTK both activate phospholipase C. b. Activation of either the GPCR or the RTK will lead to activation of transcriptional regulators. c. CaM-kinase is only activated when the GPCR is active and not when the RTK is active. d. Ras is activated only when the RTK is active and not when the GPCR is active.

c

35. 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

36. Figure 16-36 shows how normal signaling works with a Ras protein acting downstream of an RTK. You examine a cell line with a constitutively active Ras protein that is always signaling. Which of the following conditions will turn off signaling in this cell line? a. addition of a drug that prevents protein X from activating Ras b. addition of a drug that increases the affinity of protein Y and Ras c. addition of a drug that blocks protein Y from interacting with its target d. addition of a drug that increases the activity of protein Y

c

36. Vesicles from the ER enter the Golgi at the a. medial cisternae. b. trans Golgi network. c. cis Golgi network. d. trans cisternae.

c

39. Which of the following is NOT a process that delivers material to the lysosome? a. pinocytosis b. phagocytosis c. transcytosis d. autophagy

c

4. The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000 -dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be TRUE? a. Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells. b. Glial cells do not have a receptor for QGF. c. QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed. d. Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for QGF.

c

42. If you add a compound to illuminated chloroplasts that inhibits the NADP+ reductase, NADPH generation ceases, as expected. However, ferredoxin does not accumulate in the reduced form because it is able to donate its electrons not only to NADP+ (via NADP+ reductase) but also back to the cytochrome b6-f complex. Thus, in the presence of the compound, a "cyclic" form of photosynthesis occurs in which electrons flow in a circle from ferredoxin, to the cytochrome b6-f complex, to plastocyanin, to photosystem I, to ferredoxin. What will happen if you now also inhibit photosystem II? a. Less ATP will be generated per photon absorbed. b. ATP synthesis will cease. c. Plastoquinone will accumulate in the oxidized form. d. Plastocyanin will accumulate in the oxidized form.

c

43. The enzyme ribulose bisphosphate carboxylase (Rubisco) normally adds carbon dioxide to ribulose 1,5-bisphosphate. However, it will also catalyze a competing reaction in which O2 is added to ribulose 1,5-bisphosphate to form 3-phosphoglycerate and phosphoglycolate. Assume that phosphoglycolate is a compound that cannot be used in any further reactions. If O2 and CO2 have the same affinity for Rubisco, which of the following is the lowest ratio of CO2 to O2 at which a net synthesis of sugar can occur? a. 1:3 b. 1:2 c. 3:1 d. 2:1

c

45. Oxidative phosphorylation, as it occurs in modern eukaryotes, is a complex process that probably arose in simple stages in primitive bacteria. Which mechanism is proposed to have arisen first as this complex system evolved? a. electron transfers coupled to a proton pump b. the reaction of oxygen with an ancestor of cytochrome c oxidase c. ATP-driven proton pumps d. the generation of ATP from the energy of a proton gradient

c

47. Which of the phylogenetic trees in Figure 14-47 is the most accurate? Explain your answer. Note: the mitochondria and chloroplasts are from maize, but they are treated as independent "organisms" for the purposes of this question. a. Tree (a) b. Tree (b) c. Tree (c) d. Tree (d) e. Tree (e)

c

5. Which of the following statements about mitochondrial division is TRUE? a. Mitochondria divide in synchrony with the cell. b. The rate of mitochondrial division is the same in all cell types. c. Mitochondrial division is mechanistically similar to prokaryotic cell division. d. Mitochondria cannot divide and produce energy for the cell at the same time.

c

8. Foreign substances like nicotine, morphine, and menthol exert their initial effects by a. killing cells immediately, exerting their physiological effects by causing cell death. b. diffusing through cell plasma membranes and binding to transcription factors to change gene expression. c. interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus. d. removing cell-surface receptors from the plasma membrane.

c

8. 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

8. Which of the following statements describes the mitochondrial intermembrane space? a. It is permeable to molecules with molecular mass as high as 5000 daltons. b. It contains transporters for ATP molecules. c. It contains proteins that are released during apoptosis. d. It contains enzymes required for the oxidation of fatty acids.

c

8. You are studying nuclear lamins and use recombinant DNA technology to alter the coding sequence of a nuclear lamin gene. The alteration you make creates a situation 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 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 the coiled-coil formation will be disrupted.

c

10. 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

11. Electron transport is coupled to ATP synthesis in mitochondria, in chloroplasts, and in the thermophilic bacterium Methanococcus. Which of the following is likely to affect the coupling of electron transport to ATP synthesis in ALL of these systems? a. a potent inhibitor of cytochrome c oxidase b. the removal of oxygen c. the absence of light d. an ADP analog that inhibits ATP synthase

d

11. Which of the following statements about G-protein-coupled receptors (GPCRs) is FALSE? a. GPCRs are the largest family of cell-surface receptors in humans. b. GPCRs are used in endocrine, paracrine, and neuronal signaling. c. GPCRs are found in yeast, mice, and humans. d. The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

d

12. The length of time a G protein will signal is determined by the a. activity of phosphatases that turn off G proteins by dephosphorylating Gα. b. activity of phosphatases that turn GTP into GDP. c. degradation of the G protein after Gα separates from Gβγ. d. GTPase activity of Gα.

d

13. 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

16. Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as depicted in Figure 16- 16. Which of the following statements is FALSE? a. A constitutively active mutant form of PKA in skeletal muscle cells would lead to a decrease in the amount of unphosphorylated phosphorylase kinase. b. A constitutively active mutant form of PKA in skeletal muscle cells would not increase the affinity of adrenaline for the adrenergic receptor. c. A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glucose available. d. A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available.

d

16. Which component of the electron-transport chain is required to combine the pair of electrons with molecular oxygen? a. cytochrome c b. cytochrome b-c1 complex c. ubiquinone d. cytochrome c oxidase

d

16. 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. 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 these answers are correct

d

19. 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

2. During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in __________ signaling. a. endocrine b. paracrine c. neuronal d. contact-dependent

d

2. Which of the following is NOT part of the process known as "oxidative phosphorylation"? a. Molecular oxygen serves as a final electron acceptor. b. FADH2 and NADH become oxidized as they transfer a pair of electrons to the electron- transport chain. c. The electron carriers in the electron-transport chain toggle between reduced and oxidized states as electrons are passed along. d. ATP molecules are produced in the cytosol as glucose is converted into pyruvate.

d

2. 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

20. Microtubules are important for transporting cargo in nerve cell axons, as diagrammed in Figure 17-20. Notice that the two types of cargo are traveling in opposite directions. Which of the following statements is likely to be FALSE? Figure 17-20 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

20. 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

38. Stage 2 of photosynthesis, sometimes referred to as the dark reactions, involves the reduction of CO2 to produce organic compounds such as sucrose. What cofactor is the electron donor for carbon fixation? a. H2O b. NADH c. FADH2 d. NADPH

d

22. The relationship of free-energy change (ΔG) to the concentrations of reactants and products is important because it predicts the direction of spontaneous chemical reactions. In the hydrolysis of ATP to ADP and inorganic phosphate (Pi), the standard free-energy change (ΔG°) is −7.3 kcal/mole. The free-energy change depends on concentrations according to the following equation: ΔG = ΔG° + 1.42 log10 ([ADP] [Pi]/[ATP]) In a resting muscle, the concentrations of ATP, ADP, and Pi are approximately 0.005 M, 0.001 M, and 0.010 M, respectively. What is the ΔG for ATP synthesis in resting muscle? a. −6.01 kcal/mole b. 5.88 kcal/mole c. 8.72 kcal/mole d. 11.1 kcal/mole

d

23. Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels? a. lysosome → endosome → plasma membrane b. ER → lysosome → plasma membrane c. Golgi → lysosome → plasma membrane d. ER → Golgi → plasma membrane

d

25. 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

27. 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

28. Akt promotes the survival of many cells by affecting the activity of Bad and Bcl2, as diagrammed in Figure 16-28. Which of the following statements is FALSE? a. In the presence of a survival signal, Akt is phosphorylated. b. In the absence of a survival signal, Bad inhibits the cell-death inhibitor protein Bcl2. c. In the presence of a survival signal, the cell-death inhibitory protein Bcl2 is active. d. In the absence of a survival signal, Bad is phosphorylated.

d

3. 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

30. 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

30. 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

31. 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

31. Which of the following statements is FALSE? a. Nucleotides and amino acids can act as extracellular signal molecules. b. Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription. c. Some signal molecules are transmembrane proteins. d. Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids.

d

31. Which of the following statements is TRUE? a. Ubiquinone is a small, hydrophobic protein containing a metal group that acts as an electron carrier. b. A 2Fe2S iron-sulfur center carries one electron, whereas a 4Fe4S iron-sulfur center carries two electrons. c. Iron-sulfur centers generally have a higher redox potential than do cytochromes. d. Mitochondrial electron carriers with the highest redox potential generally contain copper ions and/or heme groups.

d

33. 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

34. Experimental evidence supporting the chemiosmotic hypothesis was gathered by using artificial vesicles containing a protein that can pump protons in one direction across the vesicle membrane to create a proton gradient. Which protein was used to generate the gradient in a highly controlled manner? a. cytochrome c oxidase b. NADH dehydrogenase c. cytochrome c d. bacteriorhodopsin

d

35. Photosynthesis is a process that takes place in chloroplasts and uses light energy to generate high-energy electrons, which are passed along an electron-transport chain. Where are the proteins of the electron-transport chain located in chloroplasts? a. thylakoid space b. stroma c. inner membrane d. thylakoid membrane

d

37. Consider the in vitro motility assay using purified kinesin and purified polymerized microtubules shown in Figure 17-37. 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? Figure 17-37 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

37. The ATP synthase found in chloroplasts is structurally similar to the ATP synthase in mitochondria. Given that ATP is being synthesized in the stroma, where will the F0 portion of the ATP synthase be located? a. thylakoid space b. stroma c. inner membrane d. thylakoid membrane

d

44. Which of the following statements about the possible fates of glyceraldehyde 3-phosphate is FALSE? a. It can be exported from the chloroplast to the cytosol for conversion into sucrose. b. It can be used to make starch, which is stored inside the stroma of the chloroplast. c. It can be used as a precursor for fatty acid synthesis and stored as fat droplets in the stroma. d. It can be transported into the thylakoid space for use as a secondary electron acceptor downstream of the electron-transport chain.

d

46. Below is a list of breakthroughs in energy metabolism in living systems. Which is the correct order in which they are thought to have evolved? A. H2O-splitting enzyme activity B. light-dependent transfer of electrons from H2S to NADPH C. the consumption of fermentable organic acids D. oxygen-dependent ATP synthesis a. A, C, D, B b. C, A, B, D c. B, C, A, D d. C, B, A, D

d

5. Where are chloroplast proteins translated? a. in the cytosol b. in the chloroplast c. on the endoplasmic reticulum d. in both the cytosol and the chloroplast

d

6. 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

7. 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

9. Which of the following statements describes the mitochondrial matrix? a. It is permeable to molecules with molecular mass as high as 5000 daltons. b. It contains transporters for ATP molecules. c. It contains proteins that are released during apoptosis. d. It contains enzymes required for the oxidation of fatty acids.

d

9. 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 additions 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