Deck 13: Cytoskeletal Systems

Question 1

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

Answer 1

E

Question 2

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.

Answer 2

C

Question 3

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.

Answer 3

C

Question 4

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

Question 5

Which of the following cytoskeletal proteins is found in prokaryotes?

A)keratin
B)tubulin
C)crescentin
D)vimentin
E)actin

Question 6

Microtubules have an outer diameter of

A)7 nm.
B)8-12 nm.
C)25 nm.
D)7 mm.
E)25 mm.

Question 7

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.

Question 8

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

Question 9

________ causes microtubules to form tight bundles in nerve cell axons.

A)MAP2
B)EB1
C)Tau
D)FtsZ
E)Desmin

Question 10

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.

Question 11

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.

Question 12

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.

Question 13

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.

Question 14

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.

Question 15

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.

Question 16

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.

Question 17

Cytoskeletal elements are found in

A)bacteria.
B)archaea.
C)eukaryotes.
D)B and C only.
E)A,B,and C.

Question 18

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

Question 19

Microfilaments function in

A)muscle contraction.
B)cytoplasmic streaming.
C)cell division.
D)maintenance of animal cell shape.
E)All of the above.

Question 20

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.

Question 21

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.

Question 22

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

Question 23

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

Question 24

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.

Question 25

________ 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

Question 26

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.

Question 27

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.

Question 28

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.

Question 29

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.

Question 30

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

Question 31

Actin bundles give shape and support to ________ found in intestinal mucosal cells.

A)cilia
B)flagella
C)microvilli
D)nuclei
E)lamellipodia

Question 32

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

Question 33

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.

Question 34

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

Question 35

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.

Question 36

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.

Question 37

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

Question 38

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.

Question 39

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

Question 40

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

Question 41

A network of ________,a "fourth cytoskeleton" is involved in pinching off yeast daughter cells.

Question 42

According to your text,how many classes of IFs exist?

Question 43

γ-TuRCs contain ________-tubulin and nucleate microtubule growth from MTOCs known as ________.

Question 44

The Mitchison and Kirschner ________ model of how microtubules transition between periods of growth and catastrophe proposes that ________ bound to β-tubulin subunits at a microtubule plus end stabilizes the end and promotes growth,but if the rate of hydrolysis to ________ exceeds the rate of tubulin addition,the end becomes unstable and loses subunits.

Question 45

Cancer cells retain the IF proteins from the tissue of origin even after metastasizing to other tissues.How is this important in the diagnosis and treatment of cancer?

Question 46

You have discovered a new cytoskeletal element and need to identify and characterize it for further work.How would you go about examining this protein to ultimately classify it as a cytoskeletal element?

Question 47

Describe an additional experimental approach used to study the cytoskeleton in which the activity of cytoskeletal elements is affected in ways similar to those resulting from drug treatment.

Question 48

A unique feature of ________ is that they are tissue-specific.

Question 49

The two main types of eukaryotic microtubules are the ________ and ________ microtubules.

Question 50

Cancer is a disease in which cells exhibit uncontrolled cell division.Drugs used in the study of microtubules are also used in the treatment of cancer.Why are drugs that disrupt microtubules more useful in the treatment of cancer than are drugs used to disrupt microfilaments? What is the name of the category of these drugs that describes their function?

Question 51

The ________ is a dense network of microfilaments just beneath the plasma membrane.

Question 52

Based on composition similarities,actin can be divided into two major groups: the muscle-specific actins (________-actin)and nonmuscle actins (________- and ________-actin).

Question 53

Activation of the ________ G-protein results in the extension of lamellipodia.

Question 54

________ proteins promote depolymerization of existing microtubules at the ends.

Question 55

The core of an intestinal microvillus is composed of a tight bundle of ________.

Question 56

Cytochalasins prevent addition of monomers to preexisting ________.

Question 57

Explain how the discovery of cytoskeletal elements in prokaryotes contributed to the current understanding of the endosymbiont theory.

Question 58

In the table below,list the classes of IF,the IF protein subunits,and the tissue (or cells)in which they are found.
$$\begin{array} { | l | l | l | } \hline \text { Class } & \text { IF Protein } & \text { Tissue/Cells } \\\hline & & \\\hline & & \\\hline & & \\\hline & & \\\hline & & \\\hline & & \\\hline\end{array}$$

Question 59

What are some of the drugs used to study microfilaments?

Question 60

What are some of the drugs used to study microtubules?

Question 61

What is the importance of proteins that precisely control when and where cytoskeletal elements polymerize and depolymerize? Make sure to give examples in your explanations.