Deck 15: Cytoskeletal Systems

Question 1

Critical concentration is

A)the concentration of tubulin dimers at which assembly is balanced with disassembly.
B)the concentration of tubulin dimers at which assembly occurs primarily.
C)the concentration of G-actin in most muscle cells.
D)required before nucleation can occur.
E)both choices A and D

Answer 1

A

Question 2

________ causes microtubules to form tight bundles in nerve cells.

A)Dynein
B)Actin
C)Tau
D)Kinesis
E)Tubulin

Answer 2

C

Question 3

Tubulin may assemble and disassemble simultaneously in a process known as

A)dynamic instability.
B)treadmilling.
C)microtubule organizing.
D)MAP motoring.
E)actin-regulated assembly.

Answer 3

B

Question 4

Elongation of the microtubule occurs by the

A)addition of tubulin subunits to each end.
B)addition of tubulin subunits to the (+)end.
C)addition of the tubulin subunits to the (+)end but removal from the (-)end.
D)addition of G-actin subunits to the (+)end.
E)deletion of G-actin subunits from the (+)end.

Question 5

Which of the following cytoskeletal proteins can be found in prokaryotes?

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

Question 6

Cytoskeletal elements are found in the

A)Eubacteria.
B)Archaea.
C)Eukarya.
D)choices B and C only
E)all of the above

Question 7

Intermediate filaments

A)were first discovered in muscle cells.
B)are grouped into five classes based on the cell types in which they are found.
C)have molecular masses averaging 500 kDa.
D)are smooth and sticky.
E)assemble from nonfibrous filaments.

Question 8

Capping proteins such as CapZ

A)cause microtubules to lengthen.
B)destabilize microtubules.
C)stabilize microtubules.
D)cause microtubules branching.
E)connect microtubules to microfilaments.

Question 9

Axonemal microtubules

A)are highly disorganized but very stable.
B)may be loosely associated with basal bodies.
C)are organized around a central shaft or axoneme.
D)are required to maintain axons.
E)did not become clearly recognized until better fixation techniques became available in the 1960s.

Question 10

Microtubules have an inner diameter of ________ and an outer diameter of ________.

A)15 mm; 25 mm
B)8 nm; 12 nm
C)25 nm; 30 nm
D)15 nm; 25 nm
E)7 mm; 14 mm

Question 11

Which of the following is not a function of the cytoskeleton?

A)cell movement
B)cell division
C)moving of organelles
D)positioning of enzymes
E)passive transport

Question 12

Intermediate filaments

A)can be composed of the protein vimentin.
B)are solely responsible for animal cell shape.
C)are composed of α-and β-tubulin.
D)are 70 nm in diameter.
E)both choices A and D

Question 13

Which of the following proteins is associated with the precise control of where microtubules form and depolymerize?

A)Tau
B)stathmin/Op18
C)kinesin
D)catastrophins
E)MAP 2

Question 14

Which stage of microtubule assembly is the stage in which nucleation occurs?

A)sheets of protofilaments
B)closing of microtubules
C)oligomers
D)dimers
E)elongation

Question 15

The minus (-)ends of microtubules are often anchored at the ________________ ,such that the dynamics associated with microtubules is at the plus (+)ends.

A)centriole
B)centrosome
C)plasma membrane
D)centromere
E)mitochondrial outer membrane

Question 16

Which of the following is not a cellular activity associated with microtubules?

A)maintenance of axons
B)cell shape
C)orientation of cellulose microfibrils
D)cilial structure
E)mititotic spindle

Question 17

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)cell scaffold
D)desmin sheath
E)microfilament array

Question 18

According to the current model,which of the following is the correct sequence of microtubule assembly?

A)dimers, oligomers, sheets of protofilaments, protofilaments, closing of microtubule, elongating microtubule
B)dimers, sheets of protofilaments, closing of microtubule, oligomers, protofilaments, elongating microtubule
C)dimers, oligomers, protofilaments, sheets of protofilaments, closing of microtubule, elongating microtubule
D)protofilaments, sheets of protofilaments, closing of microtubule, elongating microtubule, dimers, oligomers
E)dimers, oligomers, protofilaments, elongating microtubule, sheets of protofilaments, closing of microtubule

Question 19

A high-resolution video camera is used in which of the following microscopic techniques?

A)immunofluorescence microscopy
B)fluorescent staining of cytoskeleton proteins
C)computer-enhanced digital video microscopy
D)scanning electron microscopy
E)transmission electron microscopy

Question 20

Microfilaments function in

A)muscle contraction.
B)cytoplasmic streaming.
C)cell division.
D)maintenance of cellular shape in animal cells.
E)all of the above

Question 21

All of the following are moved by molecular motors except

A)secretory vesicles.
B)cytoskeletal filaments.
C)the Golgi complex.
D)glucose.
E)chloroplasts.

Question 22

One of the following drugs blocks cell division because it stabilizes the microtubules.What is this drug,and for what is it used?

A)vincristine; bacterial infections
B)vinblastine; antimitotic therapy
C)taxol; breast cancer
D)nocodazole; allergies
E)benzimidazole; colchicine

Question 23

A variety of proteins link actin to membranes.A ________ protein is used to link actin to the ________ membrane.

A)linker; plasma
B)spectrin; ER
C)ankyrin; lysosome
D)band 4.1; basal
E)band 4.1; mucous

Question 24

Rho GTPases have the all of the following effects on cytoskeletal actin except

A)stress fiber formation.
B)formation of pseudopodia.
C)stabilization of neurons.
D)assembly of the cytokinetic furrow.
E)regulation of endocytosis and exocytosis.

Question 25

Activation of which of the following is associated with the formation of focal adhesions and stress fibers?

A)Rho
B)Ras
C)Cdk-42
D)intermediate filaments
E)γ-tubulin

Question 26

Of the following proteins,which would be a good target for drug therapy if one needed to interfere with breaking down the microfilament network?

A)profilin
B)CapZ
C)gelsolin
D)tropomodulin
E)calmodulin

Question 27

All of the following are roles of microfilaments except

A)mitotic spindle formation.
B)muscle cell contraction.
C)amoeboid movement.
D)cytoplasmic streaming.
E)cell migration.

Question 28

Which of the following is not true of the main structural forms of actin?

A)Actin filaments may form a filament network (gel).
B)Actin monomers may form actin filaments or G-actin protein complexes.
C)Actin filaments are severed to form filament bundles.
D)Capped filaments are made from actin filaments.
E)Actin filaments form filament bundles.

Question 29

F-actin filaments

A)are composed of four linear strands.
B)are composed of polymerized G-actin monomers wound around each other in a helix.
C)are oriented similar to DNA, with strands helical and antiparallel to one another.
D)are composed of G-actin dimers.
E)polymerize at the same rate in both directions from both ends of the filament.

Question 30

Microtubules and microfilaments differ with respect to each of the following except

A)size.
B)occurrence.
C)associated motor proteins.
D)a state of dynamic instability.
E)subunits.

Question 31

Which of the following intermediate filament proteins is incorrectly matched with the tissue in which it is found?

A)cytokeratins-epithelial
B)desmin-smooth muscle
C)vimentin-mesenchymal
D)nestin-connective
E)GFA protein-nervous

Question 32

Ring-shaped complexes in the centrosome contain ________ in combination with ________.

A)α-tubulin; cilium
B)α-tubulin; γ-tubulin
C)β-tubulin; tubulin GTP
D)γ-tubulin; pericentrin
E)γ-tubulin; tubulin GTP

Question 33

Actin bundles give shape and support to the ________ found in cells of the small intestine.

A)centrosomes
B)microtubules
C)microvilli
D)nuclei
E)lamellipodia

Question 34

The microtubule-organizing center (MTOC)

A)serves as a site for microtubule and microfilament assembly.
B)acts as an anchor for both ends of the microtubule.
C)is associated with two centrioles in plant cells.
D)is called a centrosome during interphase.
E)is positioned near the cell membrane.

Question 35

________ resist tensile forces and contain keratin to form the protective barrier of the skin.

A)Intermediate filaments
B)Microtubules
C)Microfilaments
D)Actin filaments
E)Keratin-associated filaments

Question 36

In binary fission,one would expect the involvement of which of the following cytoskeletal proteins?

A)FtsZ
B)MreB
C)plaktin
D)crescentin
E)tubulin

Question 37

Of the following microtubule-interacting proteins,which might you potentially investigate as a mechanism for disrupting cell division in actively replicating tumor cells?

A)Tau
B)+-TIP proteins
C)catastrophins
D)G-actin
E)FtsZ

Question 38

Lamellipodia

A)are found in the basal lamina.
B)add structural rigidity to cells.
C)contain microtubules.
D)are thin sheets of cytoplasm use for cell movement.
E)do not involve actin or tubulin.

Question 39

Which of the following is not a function associated with the cytoskeleton?

A)scaffold for support and maintenance of cell shape
B)anchoring site for mRNA during transcription
C)cell division
D)organizes the organelles within the cytoplasm
E)signal transducer

Question 40

All of the following are components associated with the bacterial cytoskeleton except

A)FtsZ.
B)MreB.
C)plaktin.
D)crescentin.
E)both choices B and C

Question 41

________ are associated with the "pinching in" of the cell membrane during cytokinesis.

Question 42

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

Question 43

Many drugs have the ability to disrupt the cytoskeletal structure of the cell.These drugs are useful in the study of microtubules and microfilaments.
a. What are some of the drugs used to study microfilaments?
b. What are some of the drugs used to study microtubules?
c. What additional technique with applications similar to these drugs is often used to study the cytoskeleton?
d. Cancer is a disease in which cells divide uncontrollably.Many of the drugs used in the study of microtubules are also used in the treatment of cancer.From what you know about microtubules and microfilaments,can you suggest why drugs that disrupt microtubules are more useful in the treatment of cancer than drugs used to disrupt microfilaments?
e. These anticancer drugs are in a category of drugs that describes their function.What is the category?

Question 44

Cytochalasins prevent addition of monomers to pre-existing ________.

Question 45

Activation of the ________ G-protein results in the formation of focal adhesions and stress fibers.

Question 46

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

Question 47

The proteins of intermediate filaments (IFs)are tissue specific.Unlike microtubules or microfilaments,the amino acid composition of intermediate filaments varies from tissue to tissue.IFs are classified by the cell type or tissue in which they are found.
a. According to your text,how many classes of IF exist?
b. List the classes of IF,the IF proteins,and the tissue (or cells)in the table below.

c. Cells retain the IF proteins from the tissue of origin even after moving to other tissues.How is this important in the diagnosis and treatment of cancer?b.See both Table 15-4 and table below.

Question 48

The ________ model was proposed by Mitchison and Kirschner to explain how polymerization and depolymerization of microtubules occur simultaneously.

Question 49

________ are proteins that promote depolymerization of extant microtubules at the ends.

Question 50

Based upon your knowledge of the cytoskeleton,explain how the discovery of cytoskeletal elements in prokaryotes contributed to the current understanding of the endosymbiont theory.

Question 51

The structure,function,and assembly of microtubules are regulated by ________ proteins (MAPs).

Question 52

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

Question 53

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 54

The ________ model is used to describe the simultaneous polymerization and depolymerization of microtubules.

Question 55

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

Question 56

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

Question 57

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

Question 58

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