Deck 14: The Cytoskeleton and Cell Movement

Question 1

Actin filaments are approximately _______ in diameter.

A) 5 Å
B) 7 nm
C) 11 nm
D) 25 nm

Answer 1

B

Question 2

Actin exists in cells in two major forms called

A) monomers and dimers.
B) $\alpha$ -actin and $\beta$ -actin.
C) G actin and D actin.
D) G actin and F actin.

Answer 2

G actin and F actin.

Question 3

ATP is hydrolyzed by actin

A) in the process of assembly into a filament.
B) after assembly but before disassembly.
C) in the process of disassociation.
D) after disassociation from the filament.

Answer 3

B

Question 4

Each monomer of actin binds one molecule of the nucleotide triphosphate

A) ATP.
B) GTP.
C) CTP.
D) UTP.

Question 5

The phenomenon that illustrates the dynamic behavior of actin filaments and is critical to regulating the structure and function of actin filaments is known as

A) assembly.
B) dynamic instability.
C) treadmilling.
D) disassembly.

Question 6

Actin filaments are stabilized by

A) cofilin.
B) gelsolin.
C) thymosin.
D) tropomyosin.

Question 7

Branching of actin filaments can be initiated by

A) Arp2/3.
B) formin.
C) ADF/cofilin.
D) fimbrin.

Question 8

Actin filaments are bound into bundles of parallel filaments by the proteins

A) filamin and spectrin.
B) troponin and tropomyosin.
C) profilin and thymosin.
D) $\alpha$ -actinin and fimbrin.

Question 9

Short actin filaments bind to tetramers of which protein to form the cytoskeleton of erythrocytes?

A) Myosin
B) $\alpha$ -actinin
C) Spectrin
D) Ankyrin

Question 10

Which movement is not based on actin-myosin interactions?

A) Cell migration (crawling) over surfaces
B) Chromosome movement during anaphase A
C) Cytokinesis of animal cells
D) Phagocytosis

Question 11

In actin filament assembly, the process in which ATP-actin monomers are added to the barbed end of the filament while ADP-actin monomers are concurrently dissociating from the pointed end of the filament is referred to as

A) equilibrium.
B) dynamic instability.
C) treadmilling.
D) recycling.

Question 12

Duchenne's muscular dystrophy is characterized by

A) X-chromosomal inheritance.
B) childhood onset.
C) abnormal dystrophin function.
D) All of the above

Question 13

Actin filaments are anchored at junctions called

A) adherens junctions.
B) tight junctions.
C) desmosomes.
D) gap junctions.

Question 14

During muscle contraction, the A band

A) stays the same width, and the I bands and H zone shorten.
B) and H zone stay the same width, and the I bands shorten.
C) shortens, and the I bands and H zone stay the same.
D) and H zone shorten, and the I bands stay the same.

Question 15

The barbed (fast growing) end of actin filaments is located in muscle

A) at the A/I junction.
B) near the M line of a contracted sarcomere.
C) at the inner margin of the A/I zone.
D) at the Z disc.

Question 16

Myosin _______ is present in muscle sarcomeres.

A) I
B) II
C) III
D) IV

Question 17

Microtubules are typically _______ in diameter.

A) 7 nm
B) 10-12 nm
C) 25 nm
D) 35 nm

Question 18

Microtubules are assembled from

A) $\alpha$ -tubulin dimers.
B) $\beta$ -tubulin dimers.
C) alternating $\alpha$ -tubulin dimers and $\beta$ -tubulin dimers.
D) dimers of $\alpha$ - and $\beta$ -tubulin.

Question 19

Which nucleotide triphosphate is hydrolyzed during a cycle of microtubule assembly and disassembly?

A) ATP
B) TTP
C) CTP
D) GTP

Question 20

The GTP bound to $\beta$ -tubulin hydrolyzes to GDP and P_i

A) during depolymerization of the $\alpha$ - $\beta$ dimer.
B) during polymerization of dimers onto microtubules.
C) during depolymerization of dimers from microtubules.
D) following polymerization but before depolymerization.

Question 21

The microtubule behavior in which individual microtubules alternate between cycles of growth and shrinkage is called

A) an equilibrium state.
B) dynamic instability.
C) treadmilling.
D) recycling.

Question 22

Both colchicine and colcemid

A) block microtubule organizing centers.
B) block microtubule disassembly by binding to microtubule ends.
C) block microtubule assembly by binding to free tubulin.
D) accelerate microtubule disassembly by binding to tubulin in microtubules, causing those molecules to exit the microtubule more quickly.

Question 23

The anticancer drug taxol

A) blocks microtubule organizing centers.
B) stabilizes microtubules and thus inhibits disassembly.
C) blocks microtubule assembly by binding to free tubulin.
D) accelerates microtubule disassembly by binding to tubulin in microtubules, causing those molecules to exit the microtubule more quickly.

Question 24

Microtubules are not involved in

A) movement of chromosomes during mitosis.
B) transport of membranous vesicles in the cytoplasm.
C) cytokinesis of animal cells.
D) movement of cilia and flagella.

Question 25

The role of the centrosome is to

A) determine the center of the cell.
B) determine the position of the nucleus.
C) initiate microtubule growth.
D) adhere to the plus ends of microtubules.

Question 26

Rings of the protein _______ in the pericentriolar material nucleate microtubule assembly.

A) centrin
B) pericentrin
C) $\alpha$ -tubulin
D) $\gamma$ -tubulin

Question 27

At the end of interphase, the part of the microtubule farthest from the centrosome is the _______ end.

A) capped
B) barbed
C) minus
D) plus

Question 28

Kinesin I is a motor protein molecule consisting of

A) two heavy chains.
B) one heavy chain and two light chains.
C) two heavy chains and two light chains.
D) two heavy chains and four light chains.

Question 29

The cargo carried by kinesin along microtubules binds to kinesin on which region?

A) Head
B) Neck
C) Coiled-coil
D) Tail

Question 30

Kinesins are able to transport _______ along microtubules.

A) membranous vesicles
B) endoplasmic reticulum
C) mitochondria
D) All of the above

Question 31

Cytoplasmic dynein plays a key role in the positioning of which organelle?

A) Nucleus
B) Peroxisome
C) Mitochondrion
D) Golgi apparatus

Question 32

A male patient at a medical clinic presents with infertility due to nonmotile sperm and an inability to clear mucous from his respiratory tract. Other tissues are normal. You suspect that these symptoms may be caused by mutant

A) tubulin.
B) kinesin.
C) dynein.
D) tau protein.

Question 33

In a motile cilium or flagellum, _______ microtubules are arranged _______.

A) 13; in a circle
B) 9 triplet; in a circle
C) 9 doublet; in a circle around a central pair of microtubules
D) 2 microtubules; perpendicular to each other

Question 34

The basal bodies of cilia and flagella are similar in structure to (and can form from)

A) centromeres.
B) kinetomeres.
C) kinetochores.
D) centrioles.

Question 35

Adjacent microtubule doublets in cilia and flagella produce a bending movement because

A) tubulin is contracting on one side of the microtubules.
B) dynein is contracting on one side of the microtubules.
C) kinesin is contracting on one side of the microtubules.
D) nexin links between microtubule doublets convert a sliding movement into a bending movement.

Question 36

The beating of cilia and flagella occurs by means of _______-based _______.

A) dynein; microtubule sliding
B) kinesin; microtubule sliding
C) myosin; microfilament sliding
D) tubulin; microtubule contraction

Question 37

The microtubules that overlap in the center of the mitotic spindle are called _______ microtubules.

A) astral
B) minus-end
C) kinetochore
D) interpolar

Question 38

The drug taxol stabilizes microtubules so they cannot shorten. If taxol were added during anaphase of mitosis, what effect would you expect it to have on anaphase movements?

A) It would stop all movements.
B) It would stop anaphase A but not anaphase B.
C) It would stop anaphase B but not anaphase A.
D) It would have no effect.

Question 39

The intermediate filaments in the nucleus are made of

A) keratins.
B) lamins.
C) desmin.
D) vimentin.

Question 40

The desmin filaments in muscle cells connect

A) actin filaments to the Z line.
B) actin filaments to the plasma membrane at the ends of myofibrils.
C) Z lines of adjacent myofibrils.
D) myosin filaments to the Z line.

Question 41

Keratin filaments are found in which of the following cell types?

A) Fibroblasts
B) Adipocytes
C) Muscle cells
D) Epithelial cells

Question 42

Vimentin is the major intermediate filament protein of _______ cells.

A) epithelial
B) striated muscle
C) nerve
D) fibroblast

Question 43

Intermediate filaments are typically _______ in diameter.

A) 5-7 nm
B) 10-12 nm
C) 16-22 nm
D) 24-26 nm

Question 44

Intermediate filaments function in

A) cell motility.
B) providing mechanical strength for cells.
C) nuclear pore structure.
D) All of the above

Question 45

Keratin filaments are anchored to junctions called

A) adherens junctions.
B) tight junctions.
C) desmosomes.
D) gap junctions.

Question 46

Which protein can link intermediate filaments with actin filaments and microtubules?

A) $\alpha$ -actinin
B) $\beta$ -catenin
C) Integrin
D) Plectin

Question 47

Expression of a shortened skin keratin gene in place of the normal keratin gene in transgenic mice results in a phenotype in which mice have

A) thick skin.
B) no hair.
C) fragile, easily blistered skin.
D) white hair.

Question 48

The complex network of protein filaments and microtubules that extends throughout the cytoplasm is called the _______.

Question 49

The three types of filaments that provide the basis of cell shape and cell motility in eukaryotes are actin filaments, intermediate filaments, and _______.

Question 50

Most myosins move along actin filaments toward the _______ end.

Question 51

When a striated muscle is stimulated to contract, calcium is released primarily from the _______ and interacts with a group of three thin-filament proteins called _______, which in turn cause the long, thin protein _______ to move away from the cross-bridge binding sites on the _______ molecules. This allows the cross-bridge cycle to occur.

Question 52

The initial role of ATP in the cross-bridge cycle is to bind to _______ and cause it to _______.

Question 53

The motor protein that moves cargo toward the minus ends of microtubules is _______.

Question 54

The motor protein that moves cargo toward the plus ends of microtubules is _______.

Question 55

Dynein and kinesin are similar in that they consist of heavy chains with globular heads that bind both _______ and _______.

Question 56

The intermediate filament protein _______ is the major protein of the human skin, hair, and fingernails. The most prominent secondary structure in this protein is the _______. The monomers of this protein associate first to form dimers and then are assembled into protofilaments, _______ (number) of which associate laterally to form an intermediate filament.

Question 57

In cells, actin filaments form a network that provides mechanical support, determines cell shape, and allows for movement of the cell surface.

Question 58

Actin exists in two forms, a globular G form and a filamentous F form.

Question 59

Formation of actin filaments requires energy in the form of ATP.

Question 60

Actin may be cross-linked into antiparallel bundles.

Question 61

In muscle, every myofibril is organized as a chain of contractile units called myocytes.

Question 62

Microtubules are approximately 1/3 the diameter of actin filaments.

Question 63

The cycle of alternating growth and shrinkage of microtubules is referred to as dynamic instability, or rescue and catastrophe.

Question 64

Kinesins and dyneins are molecular motor proteins.

Question 65

Epidermolysis bullosa simplex is a skin disease caused by a mutation in the gene encoding keratin.

Question 66

Desmosomes are specialized junctions that help hold cells together, while their counterpart hemidesmosomes prevent cell-to-cell contact.

Question 67

What is the normal function of dystrophin in muscle cells?

Question 68

Nebulin filaments attach to actin filaments in muscle for what purpose?

Question 69

Describe the myosin II molecule and its component parts.

Question 70

What is a sarcomere? (Include the structures that bound it in your definition.)

Question 71

How is contraction regulated in smooth muscle?

Question 72

How are the plus and minus ends of microtubules arranged in the dendrites of neurons?

Question 73

What is the polarity of microtubule assembly in an axon of a nerve?

Question 74

What MAP is the main component of the lesions found in the brains of Alzheimer's patients?

Question 75

In which directions do kinesin and dynein transport vesicles in an axon?

Question 76

Describe the two separate mechanisms by which the poles of the mitotic spindle move apart in anaphase B.

Question 77

Intermediate filament proteins vary in size but share structural features. Describe these shared features.

Question 78

Which of the following is not one of the functions of the cytoskeleton?

A) To provide a structural framework for the cell
B) Cell locomotion
C) Protein translocation into the ER
D) Intracellular movement of organelles and other structures

Question 79

The approximate diameter of an actin filament is

A) 7 nm.
B) 10-12 nm.
C) 25 nm.
D) 5 mm.

Question 80

Which of the following is not true of the assembly of actin filaments?

A) It begins with the formation of an aggregate of three actin monomers.
B) It requires ATP.
C) Polymerization occurs from both the plus and minus ends.
D) Polymerization is faster from the plus end than from the minus end.