Chapter 13: Cytoskeletal system
Which of the following cytoskeletal proteins would be expected to be involved in binary fission of a bacterium into two bacteria? A) FtsZ B) MreB C) plectin D) crescentin E) tubulin
A) FtsZ
Which of the following is not known to be involved in associating actin microfilaments with plasma membranes? A) PIP2 B) spectrin C) ankyrin D) band 4.1 E) A, B, C, and D are involved in associating actin microfilaments with plasma membranes.
A) PIP2
The ________ is a complex network of interconnected filaments and tubules that extends throughout the cytosol from the nucleus to the inner surface of the plasma membrane. A) cytoskeleton B) microtubule apparatus C) axoneme D) desmin sheath E) microfilament array
A) cytoskeleton
Mutations of keratins in the ________ that resist tensile forces in the skin cause the blistering disease known as epidermolysis bullosa simplex. A) intermediate filaments B) microtubules C) microfilaments D) actin filaments E) crescentin filaments
A) intermediate filaments
Which phase of microtubule polymerization in vitro would be affected most by adding short microtubules to unpolymerized GTP-tubulin? A) lag phase B) elongation phase C) addition of tubulin dimers to microtubule (+) ends at the plateau phase D) addition of tubulin dimers to microtubule (−) ends at the plateau phase E) treadmilling
A) lag phase
Axonemal microtubules are A) dynamically unstable. B) anchored on basal bodies. C) randomly oriented in the axoneme. D) required to maintain axons. E) involved in intracellular organelle transport.
B) anchored on basal bodies.
Microfilaments A) are composed of eight protofilaments joined end to end with staggered overlaps. B) are composed of two helical strands of actin monomers oriented in the same direction. C) are composed of two helical antiparallel strands of actin monomers. D) are composed of α- and β-actin dimers. E) polymerize at the same rate from both ends of the filament.
B) are composed of two helical strands of actin monomers oriented in the same direction.
Intermediate filaments A) are 7 nm in diameter. B) can be composed of the protein vimentin. C) are abundant in plant cells. D) are the only cytoskeletal filament responsible for animal cell shape. E) A, B, C, and D.
B) can be composed of the protein vimentin.
Microtubules and microfilaments are similar with respect to each of the following except A) inherent polarity of the structure. B) localization similar to that of intermediate filaments in cells. C) association with motor proteins. D) plus and minus ends for polymerization. E) both are polymers of subunits.
B) localization similar to that of intermediate filaments in cells.
Profilin does all of the following except A) competes with thymosin β4 for binding to actin monomers. B) sequesters actin monomers to prevent any polymerization. C) binds to formin in order to "stage" actin monomers for addition to a growing filament. D) promotes actin monomer addition to a filament plus end. E) Profilin does all of the above.
B) sequesters actin monomers to prevent any polymerization.
Tubulin may assemble onto one end while disassembling from the other end of the same microtubule simultaneously in a process known as A) dynamic instability. B) treadmilling. C) nucleation. D) oligomerization. E) catastrophe-rescue.
B) treadmilling.
The critical concentration for tubulin polymerization is the concentration of A) tubulin dimers at which all dimers assemble into microtubules. B) unassembled tubulin dimers when assembly is balanced with disassembly. C) tubulin dimers at which dimers assemble onto microtubule minus ends but disassemble from plus ends. D) unassembled tubulin dimers when there is net disassembly of dimers from both microtubule ends. E) tubulin dimers in most cells.
B) unassembled tubulin dimers when assembly is balanced with disassembly.
Microtubules have an outer diameter of A) 7 nm. B) 8—12 nm. C) 25 nm. D) 7 mm. E) 25 mm.
C) 25 nm.
Which of the following microtubule-interacting proteins would you target to disrupt cell division in actively replicating tumor cells? A) Tau B) EB1 (a +-TIP protein) C) MCAK (a catastrophin) D) plectin (a spectraplakin) E) MAP2
C) MCAK (a catastrophin)
Activation of which of the following is associated with the formation of focal adhesions and stress fibers? A) Cdc42 B) plectin C) Rho D) Rac E) γ-tubulin
C) Rho
________ causes microtubules to form tight bundles in nerve cell axons. A) MAP2 B) EB1 C) Tau D) FtsZ E) Desmin
C) Tau
________ is a drug that blocks cell division by stabilizing microtubules; as a result, it is used in the treatment of ________. A) Vincristine; listeriosis B) Vinblastine; lung cancer C) Taxol; breast cancer D) Nocodazole; athlete's foot E) Colchicine; gout
C) Taxol; breast cancer
Which of the following is false about lamellipodia? A) Their formation is stimulated by activation of Rac. B) They may have associated filopodia. C) They contain bundles of microtubules that push the plasma membrane forward. D) They extend at the leading edge of crawling cells. E) They contain branched networks of actin filaments.
C) They contain bundles of microtubules that push the plasma membrane forward.
Dynamic assembly and disassembly of a cytoplasmic microtubule in a cell occurs primarily at its plus end, because its minus end is usually anchored to A) a basal body. B) a centromere. C) a microtubule organizing center. D) a mitochondrial outer membrane. E) the plasma membrane.
C) a microtubule organizing center.
Which technique would best be used to visualize movement of unlabeled vesicles along microtubules? A) immunofluorescence microscopy of fixed material B) live cell fluorescence microscopy C) computer-enhanced digital video microscopy D) deep-etch electron microscopy E) A, B, C, or D would be equally useful.
C) computer-enhanced digital video microscopy
Which of the following cytoskeletal proteins is found in prokaryotes? A) keratin B) tubulin C) crescentin D) vimentin E) actin
C) crescentin
Which of the following is not associated with the bundle of microfilaments supporting each microvillus in small intestine mucosal cells? A) fimbrin B) villin C) fascin D) myosin I E) All are associated with the microvillus microfilament bundle.
C) fascin
Which of the following proteins would be a good drug target for interfering with microfilament network breakdown? A) profilin B) CapZ C) gelsolin D) tropomodulin E) calmodulin
C) gelsolin
Actin bundles give shape and support to ________ found in intestinal mucosal cells. A) cilia B) flagella C) microvilli D) nuclei E) lamellipodia
C) microvilli
Rho Family GTPases (Rho, Rac, Cdc42) stimulate cytoskeletal microfilament assembly for all of the following except A) stress fiber formation. B) lamellipodia formation. C) nuclear envelope breakdown for mitosis. D) cytokinetic furrow formation. E) filopodia formation
C) nuclear envelope breakdown for mitosis.
All of the following are components associated with bacterial cytoskeletons except A) FtsZ. B) MreB. C) plectin. D) crescentin. E) A, B, C, and D are associated with the bacterial cytoskeletons.
C) plectin.
CapZ A) causes microfilaments to lengthen by assembly at their plus ends. B) depolymerizes microfilaments at their plus ends. C) prevents assembly and disassembly at microfilament plus ends. D) forms microfilament branches. E) connects microfilaments to microtubules.
C) prevents assembly and disassembly at microfilament plus ends.
A microtubule-organizing center (MTOC) A) contains centrioles in plant cells. B) serves as a site for both microtubule and intermediate filament assembly. C) anchors either end of cytoplasmic microtubules. D) anchors only the minus ends of cytoplasmic microtubules. E) usually is positioned near the cell membrane.
D) anchors only the minus ends of cytoplasmic microtubules.
Which of the following proteins is associated with the precise control of where microtubules depolymerize during mitosis? A) Tau B) stathmin/Op18 C) gelsolin D) catastrophins E) MAP 2
D) catastrophins
Microtubules contribute to each of the following except A) intracellular transport. B) the human red blood cell disklike shape. C) orientation of plant cellulose microfibrils. D) filopodial structure. E) mitotic spindles.
D) filopodial structure.
Which of the following intermediate filament proteins is incorrectly matched with the cell type in which it is found? A) keratin - epithelial cells B) desmin - smooth muscle cells C) vimentin - mesenchymal cells D) nestin - connective tissue cells E) GFA protein - glial cells
D) nestin - connective tissue cells
Which of the following is true about the structure of the microtubule wall? A) α-β-tubulin heterodimers are arranged with mixed orientation in each protofilament, and protofilaments are arranged with mixed polarity in the microtubule wall. B) α-β-tubulin heterodimers are arranged with the same orientation in each protofilament, and protofilaments are arranged with mixed polarity in the microtubule wall. C) α-β-tubulin heterodimers are arranged with the mixed orientation in each protofilament, and protofilaments are arranged with same polarity in the microtubule wall. D) α-β-tubulin heterodimers are arranged with the same orientation in each protofilament, and protofilaments are arranged with same polarity in the microtubule wall. E) Orientation of the α-β-tubulin heterodimers is completely random and depends on which end of the dimer first hits the end of the microtubule when it assembles.
D) α-β-tubulin heterodimers are arranged with the same orientation in each protofilament, and protofilaments are arranged with same polarity in the microtubule wall.
Centrosome ring-shaped complexes contain ________ and ________. A) α-tubulin; β-tubulin B) γ-tubulin; MCAK C) γ -tubulin; MAP2 D) γ-tubulin; GRiPs E) γ-tubulin; crescentin
D) γ-tubulin; GRiPs
Which of the following is false about dynamic instability of a microtubule end? A) During a growth phase, assembly of GTP-tubulin is faster than incorporated GTP is hydrolyzed, forming a GTP-cap. B) During a catastrophe phase, hydrolysis of incorporated GTP is faster than GTP-tubulin addition, forming a GDP-cap. C) During rescue, GTP-tubulin assembles fast enough to reestablish a GTP cap. D) Each end of a microtubule can undergo dynamic instability independently. E) A, B, C, and D are true.
E) A, B, C, and D are true.
Cytoskeletal elements are found in A) bacteria. B) archaea. C) eukaryotes. D) B and C only. E) A, B, and C.
E) A, B, and C.
Intermediate filaments A) lack the intrinsic polarity of microtubules and microfilaments, because IF tetrameric subunits are symmetric. B) are grouped into five cytoplasmic classes based on the cell types in which they are found and one nuclear class. C) are the most stable and least soluble cytoskeleton filaments. D) are not found in plant cell cytoplasm. E) All of the above are true.
E) All of the above are true.
Microfilaments function in A) muscle contraction. B) cytoplasmic streaming. C) cell division. D) maintenance of animal cell shape. E) All of the above.
E) All of the above.
Actin filaments may form each of the following except A) 3D filament networks (gels). B) contractile bundles. C) branched networks. D) bundles of parallel filaments. E) axonemes containing doublet microfilaments.
E) axonemes containing doublet microfilaments.
What is the effect of cofilin on an actin microfilament? A) caps the microfilament plus end B) caps the microfilament minus end C) increases turnover of ATP-actin at the microfilament plus end D) increases turnover of ADP-actin at the microfilament plus end E) increases turnover of ADP-actin at the microfilament minus end
E) increases turnover of ADP-actin at the microfilament minus end
Which of the following is not a function of the cytoskeleton? A) cell locomotion B) cell division C) organelle movement D) establishing cell shape E) passive transport
E) passive transport