Lodish 8e Chapter 17 Test Bank PDF

17 Cell Organization and Movement I: Microfilaments *Section 17.1* 1\. The plasma membrane of eukaryotic cells is supported by: a\. actin filaments. b\. microtubules. c\. lamins. d\. intermediate filaments. Ans: a Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty:...

17 Cell Organization and Movement I: Microfilaments *Section 17.1* 1\. The plasma membrane of eukaryotic cells is supported by: a\. actin filaments. b\. microtubules. c\. lamins. d\. intermediate filaments. Ans: a Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 2\. Three major groups of filament systems comprising the cytoskeleton are all composed of polymers of assembled subunits, which vary in thickness when assembled. Which is the correct order, from smallest to largest, of the filament systems? a\. microtubules, microfilaments, intermediate filaments b\. intermediate filaments, microtubules, microfilaments, c\. microfilaments, microtubules, intermediate filaments d\. none of the above Ans: d Question Type: Multiple choice Chapter: 17 Blooms: Applying Difficulty: Moderate *Section 17.2* 3\. Actin-binding proteins that generate actin filament bundles: a\. are long and flexible. b\. bind only to the ends of actin filaments. c\. can also bundle microtubules. d\. are short and inflexible. Ans: d Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Moderate 4\. Decoration of actin filaments with myosin S1 is commonly used to: a\. attach actin filaments to cell membranes. b\. disassemble actin filaments. c\. reveal the polarity of actin filaments. d\. reveal the polarity of myosin filaments. Ans: c Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Easy 5\. Many actin cross-linking proteins contain: a\. an ATP-binding cleft. b\. a head domain. c\. a CH domain. d\. only one actin-binding site. Ans: c Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Moderate 6\. Within an actin filament, each actin subunit is surrounded by \_\_\_\_\_ neighboring actin subunits. a\. one b\. two c\. four d\. eight Ans: c Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Moderate 7\. How do actin filaments appear when viewed by negative stain electron microscopy? Ans: When viewed by negative stain electron microscopy, an actin filament appears as a twisted string of beads with a diameter of 7--9 nm. Question Type: Essay Chapter: 17 Blooms: Remembering Difficulty: Easy 8\. What cellular components cause some actin filaments to form bundles and others to form networks? Ans: Different actin-binding proteins (ABPs) cause actin filaments to cluster together in different ways. While all ABPs have two actin-binding sites, those ABPs that promote bundle formation tend to be short and inflexible, whereas the ABPs that promote network formation tend to be longer and more flexible. Question Type: Essay Chapter: 17 Blooms: Remembering Difficulty: Moderate 9\. At ATP-G-actin concentrations that are intermediate between the Cc for the (+) end and the Cc for the (--) end,\_\_\_\_\_ will be observed. The Cc needed for elongation at the (+) end is \_\_\_\_\_ than that at the (--) end of actin microfilaments. a\. growth; lower b\. shrinking, higher c\. treadmilling, lower d\. none of the above Ans: c Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Moderate *Section 17.3* 10\. All of the following statements about actin assembly are correct EXCEPT: a\. ATP-actin can assemble into filaments. b\. actin subunits can treadmill through an actin filament. c\. actin assembly can produce force for movement. d\. actin (−) ends assemble more rapidly than actin (+) ends. Ans: d Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Moderate 11\. Gelsolin is activated by: a\. ATP binding. b\. phosphorylation. c\. Ca^2+^ binding. d\. dephosphorylation. Ans: c Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 12\. During treadmilling, actin subunits add: a\. predominantly to filament (+) ends. b\. predominantly to filament (−) ends. c\. equally to both filament ends. d\. along the length of filaments. Ans: a Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Moderate 13\. Which of the following proteins promotes actin assembly and is involved in signaling pathways controlling actin assembly at the plasma membrane? a\. myosin b\. profilin c\. thymosin β4 d\. filamin Ans: b Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 14\. *Listeria* is a bacterial parasite that has evolved unique ways to enter animal cells and then use actin polymerization for its intracellular movement. Which of the following statements is true in regards to *Listeria* and actin polymerization? a\. *Listeria* ActA protein binds and inactivates the Arp2/3 complex. b\. *Listeria* ActA binds VASP, which enhances ATP-actin assembly. c\. Cofilin is necessary to accelerate the assembly of the (−) end of the filament. d\. CapZ promotes the elongation of the filament. Ans: b Question Type: Multiple choice Chapter: 17 Blooms: Applying Difficulty: Moderate 15\. What actin-binding protein mediates gel-sol transitions, and how is this protein's activity regulated? Ans: Gel-sol transitions are mediated by gelsolin, an actin-binding protein that severs actin filaments and caps the (+) ends of the resulting fragments. Gelsolin is activated by Ca^2+^ binding. Question Type: Essay Chapter: 17 Blooms: Understanding Difficulty: Easy 16\. What is the function of thymosin β~4~? Ans: Thymosin β~4~ is a G-actin sequestering protein that functions to maintain a relatively high G-actin concentration in cells. Presumably, the cell can access this G-actin pool when new filament assembly is needed. Question Type: Essay Chapter: 17 Blooms: Applying Difficulty: Moderate 17\. A well-coordinated mechanism involving cell-surface receptors and the actin cytoskeleton allows leukocytes to bind and engulf invading bacteria. Briefly describe how bacteria are phagocytosed. Ans: In a process termed opsonization, antibodies circulating in the blood recognize surface proteins on the bacteria. The Fc region of the bound antibodies is then recognized by specific receptors on the leukocyte cell surface, causing the cell to begin engulfing the bacterium. Binding also leads to the assembly of an actin network at the engulfment site where, together with myosin, force is generated to draw the bacteria into the cell. Eventually, the bacterium is completely engulfed, forming a phagosome in the leukocyte. The phagosome fuses to lysosomes, where acidic enzymes kill and degrade the bacterium. Question Type: Essay Chapter: 17 Blooms: Understanding Difficulty: Moderate 18\. Which of the following is a G-actin sequestering protein that allows cells to maintain a relatively high G-actin concentration in cells? a\. thymosin β~4~ b\. FH2 domain of formin c\. profilin d\. cofilin Ans: a Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Easy 19\. Cofilin: a\. cleaves actin by binding the ATP-actin in the filament. b\. cleaves actin by twisting adjacent F-actin monomers in the filament. c\. recruits G-actin monomers to the elongating F-actin microfilament. d\. promotes exchange of ADP for ATP on G actin. Ans: b Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Moderate 20\. If the activity of thymosin β4 was inhibited in fibroblasts, the overall effect would be: a\. a decrease in cell locomotion because less actin would be recruited to the leading edge. b\. an increase in cell locomotion because there would be a higher concentration of actin available. c\. no change in cell locomotion because thymosin β4 doesn't interact with Rho, Rac, or Cdc42. d\. none of the above Ans: b Question Type: Multiple choice Chapter: 17 Blooms: Applying Difficulty: Moderate 21\. The two proteins that play the most important role in actin microfilament elongation are: a\. thymosin β4 and cofilin. b\. cofilin and profilin. c\. profilin and thymosin β4. d\. CapZ and cofilin. Ans: c Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Easy 22\. What would occur if CapZ was inhibited in cells? a\. increased organization of actin in stereocilia due to stabilized actin dynamics b\. increased rates of polymerization due to reduced availability for ADP-G-actin c\. increased steady-state treadmilling of F-actin d\. faster movement of cells toward a chemical signal Ans: c Question Type: Multiple choice Chapter: 17 Blooms: Analyzing Difficulty: Moderate *Section 17.4* 23\. Which of the following proteins is involved in formation of actin bundles in microvilli by providing crosslinks between actin filaments? a. α actinin b\. cofilin c\. fimbrin d\. profilin Ans: c Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 24\. Human erythrocytes depend on microfilament networks to provide strength and flexibility. Describe this network and explain how microfilaments are attached to the plasma membrane in human erythrocytes. Ans: The microfilament network that underlies the plasma membrane in human erythrocytes is based on short actin filaments of about 28 subunits in length. These are held together in "hubs" by six spectrin molecules. Overall, this creates a fishnet structure. The network is attached to the plasma membrane in two ways. The protein ankyrin links the microfilament network to the bicarbonate transporter in the plasma membrane, and band 4.1 protein links the network to glycophorin C. Question Type: Essay Chapter: 17 Blooms: Understanding Difficulty: Moderate 25\. How do the different types of actin-binding proteins relate to the ability of actin to form bundles *and* networks? a\. Proteins promoting bundle formation have one actin-binding site, whereas proteins promoting network formation have two actin-binding sites. b\. Different types of actin bind different actin-binding proteins to form bundles or networks. c\. Proteins that promote bundle formation bind ADP-actin, whereas proteins that promote network formation bind ATP-actin. d\. Proteins promoting bundle formation tend to be short and inflexible, whereas proteins that promote network formation tend to be longer and more flexible. Ans: d Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Moderate *Section 17.5* 26\. Which region of myosin interacts with actin filaments? a\. the head domain b\. the rod domain c\. the light chains d\. the tail domain Ans: a Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 27\. Which of the following properties is not shared by all myosins? a\. the ability to bind ATP b\. the ability to form dimers c\. the ability to bind actin d\. the presence of a head domain Ans: b Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 28\. All myosins move toward the (+) end of actin filaments EXCEPT: a\. myosin I. b\. myosin II. c\. myosin V. d\. myosin VI. Ans: d Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 29\. Describe the functional properties of the head, neck, and tail domains of myosin. Ans: The head domain of myosin is a specialized ATPase that couples the hydrolysis of ATP with motion. The activity of the myosin-ATPase is activated by binding to actin. The neck is an α-helical region that is critical for converting small conformational changes in the head domain into large movements of the molecule and for regulating the activity of the head domain. The tail domain contains the binding sites for other molecules such as the thick filament in muscle. Question Type: Essay Chapter: 17 Blooms: Understanding Difficulty: Moderate *Section 17.6* 30\. In the operational model for movement of myosin along an actin filament, the power stroke occurs during: a\. binding of ATP. b\. hydrolysis of ATP. c\. release of phosphate (Pi). d\. release of ADP. Ans: c Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 31\. What is the function of CapZ and tropomodulin in the sarcomere? a\. to center myosin thick filaments b\. to attach actin thin filaments to the Z disk c\. to maintain a constant actin thin filament length d\. to make contraction sensitive to Ca^2+^ Ans: c Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Moderate 32\. In the budding yeast *S. cerevisiae,* which of the following is NOT transported into the bud by myosin V? a\. peroxisome b\. vacuole c\. mRNA d\. nucleus Ans: d Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 33\. Multinucleated cells may result from a defect in: a\. myosin V. b\. myosin I. c\. stress fiber formation. d\. myosin II. Ans: d Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Moderate 34\. What are the functions of the myosin head domain and tail domain, respectively? Ans: The myosin head domain is the portion of the motor protein that binds actin filaments and uses the energy from ATP hydrolysis to generate movement along the filament. All types of myosins have similar head domains. The myosin tail domain acts to recognize and bind cellular cargo. Each type of myosin has a different tail domain and thus can potentially move a different kind of cargo (although myosin II forms a bipolar filament). Question Type: Essay Chapter: 17 Blooms: Understanding Difficulty: Moderate 35\. What contractile structure is essential for cell division? Ans: The contractile ring is a transient contractile bundle formed toward the end of mitosis. It is laterally attached to the cell membrane, and as the ring contracts, the plasma membrane is brought together between the spindle poles until the membrane fuses and two new cells are created. Question Type: Essay Chapter: 17 Blooms: Remembering Difficulty: Moderate 45\. Which of the following is NOT a function of myosin-powered movements? a\. skeletal muscle contraction b\. cytoplasmic streaming c\. cytokinesis d\. flagellum-mediated cell motility Ans: d Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy *Section 17.7* 36\. Membrane extension during cell locomotion is driven by: a\. myosin II. b\. actin depolymerization. c\. contraction. d\. actin polymerization. Ans: d Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 37\. Lamellipodia are located: a\. at a moving cell's trailing edge. b\. at a moving cell's leading edge. c\. around the entire periphery of a nonmotile cell. d\. throughout the cytosol of a moving cell. Ans: b Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 38\. The elastic Brownian ratchet model has been proposed to explain: a\. membrane extension. b\. focal adhesion formation. c\. cell-body translocation. d\. gel-sol transitions. Ans: a Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Easy 39\. Small G proteins, including Rho, Rac, and Cdc42, contribute to the coordinated movement and overall polarity of a migrating cell. Assuming that the cell is migrating in a left-to-right fashion, which of the following is correct? a\. active Cdc42 at the leading edge of the cell and active Rho at the back of the cell b\. active Rac at the back of the cell and active Cdc42 at the front of the cell c\. active Cdc42 at the back of the cell and active Rac at the leading edge of the cell d\. active Rac at the leading edge of the cell and active Rho at the back of the cell Ans: a Question Type: Multiple choice Chapter: 17 Blooms: Analyzing Difficulty: Moderate 40\. How do cells grip the substrate to generate locomotion? Ans: Locomoting cells use focal adhesions to get a grip on substrate material (e.g., the extracellular matrix). Focal adhesions are complexes of many different proteins, which form at the leading edge of moving cells just after membrane extension and dissolve (or are left behind) at the rear end of the moving cell. Question Type: Essay Chapter: 17 Blooms: Understanding Difficulty: Easy 41\. How are actin-binding proteins involved in gel-sol transitions? Ans: The transformation between sol and gel states results from the disassembly and reassembly of actin networks in the cytosol. Proteins such as cofilin sever actin filaments to form the sol state, whereas profilin promotes actin assembly, and α-actinin and filamin form the networks needed for the transition to the gel state. Question Type: Essay Chapter: 17 Blooms: Understanding Difficulty: Easy 42\. Like *Listeria*, other bacterial pathogens have also evolved to take advantage of actin-based cell motility systems in their hosts. For example, some pathogenic strains of *E. coli* make a cytotoxic factor (CNF1) that converts a specific glutamine residue on RhoGTPases to glutamate. This change blocks both the intrinsic and GAP-stimulated GTP hydrolysis activity of the Rho protein. Predict the effects of CNF1 on human epithelial cells in culture. Ans: If GTP hydrolysis were blocked, Rho would remain constitutively active. Similar to the effects of dominant active Rho mutants, this would result in the formation of stress fibers in the tissue culture cells. (Stress fiber formation would allow the cultured epithelial cells to spread.) Reference for the data cited in this question: Fiorentini, C., et al. 1997. *Escherichia coli* Cytotoxic Necrotizing Factor I (CNF1), a Toxin That Activates the Rho GTPase. *J. Biol. Chem.* 272(31):19532--19537. Question Type: Essay Chapter: 17 Blooms: Analyzing Difficulty: Moderate 43\. The correct order of events in cell locomotion is: a\. rear focal adhesion, membrane protrusion, front focal adhesion, cell body translocation, de-adhesion. b\. membrane protrusion, front focal adhesion, cell body translocation, de-adhesion, rear focal adhesion. c\. front focal adhesion, cell body translocation, de-adhesion, rear focal adhesion, membrane protrusion. d\. cell body translocation, de-adhesion, rear focal adhesion, membrane protrusion, front focal adhesion. Ans: a Question Type: Multiple choice Chapter: 17 Blooms: Understanding Difficulty: Easy 44\. In response to a chemotactic signal, a cell forms structures to aid in locomotion. In lamellipodia, active Rac will stimulate F-actin polymerization at the leading edge via \_\_\_\_\_, whereas actin that will form stress fibers will be recruited by formin downstream of activation of this small GTPase \_\_\_\_\_. a\. Arp 2/3; Rho b\. Arp 2/3; Cdc42 c\. WASP; Rho d\. Rho kinase; Cdc42 Ans: a Question Type: Multiple choice Chapter: 17 Blooms: Remembering Difficulty: Moderate 45\. In a scratch wound assay, cells are treated with inhibitors of Rho kinase. What would be observed? a\. The cells completely close the scratch, and only lamellipodia and filapodia are seen with actin staining. b\. The distance the cells migrate into the scratch is small, and actin staining reveals stress fibers, lamellipodia, and filapodia. c\. The cells are stimulated to undergo mitosis. d\. The cells migrate into the scratch, but no stress fibers can be observed with actin staining. Ans: b Question Type: Multiple choice Chapter: 17 Blooms: Analyzing Difficulty: Difficult