What happens to the Z lines after contraction of the sarcomere?

a) The distance between the Z lines does not change.
b) The distance between the Z lines decreases.
c) The distance between the Z lines increases.
d) The Z lines disappear.
e) The Z lines become curved.

Which type of cytoskeletal element is characterized as a hollow, rigid cylindrical tube with walls
composed of tubulin subunits?

a) microfilaments
b) microtubules
c) intermediate filaments
d) all of these choices
e) minitubules

Which type of cytoskeletal element is described as tough, ropelike fibers composed of a variety of
related proteins like keratin?

a) microfilaments
b) microtubules
c) intermediate filaments
e) macrofilaments

You use a nonionic detergent to extract a cell. When you do, much of the mRNA stays behind with the
cytoskeleton, which is not solubilized by this treatment. What do these results mean?

a) The cytoskeleton denatures in nonionic detergents.
b) The mRNA is solubilized by the nonionic detergents.
c) The mRNA is anchored to the cytoskeleton.
d) The cytoplasm is anchored to the mRNA.
e) The cytoskeleton is destabilized by the nonionic detergent.

The splitting of a parent cell into two daughter cells is called ______.

a) diakinesis
b) cytokinesis
c) mitosis
d) meiosis
e) cytomegaly

Fluorescence microscopy allows investigators to view things _________ of regular light microscopes.

a) above the limits of resolution
b) above the limits of magnification
c) below the limits of resolution
d) below the limits of magnification
e) at the limits of magnification

When laser beams are shone through the objective lens of a microscope, a weak attractive force is generated near the point of focus. This allows the grasping of microscopic objects. Such a device is called a(n) ______.

a) optical density
b) optical tweezer
c) confocal laser scanning
d) absorbance microscopy
e) laser pointer

In an attempt to monitor the movement of individual kinesin molecules labeled with GFP along microtubules labeled with a red fluorescent dye using an in vitro motility assay, what specialized type of laser-based fluorescence microscopy would be most likely to be employed?

a) FRAP
b) TIRF
c) total internal reflection microscopy
d) atomic force microscopy
e) TIRF and total internal reflection microscopy

TIRF works by _________________.

a) chemically dissecting microtubules
b) focusing on a very thin plane just above the surface on which microtubules are lying
c) by preventing light rays emanating from individual motor proteins being monitored from being obscured by light rays from other areas
d) focusing on a very thin plane just above the surface on which microtubules are lying and by preventing light rays emanating from individual motor proteins being monitored from being obscured by light rays from other areas
e) denaturing the tubulin subunits of microtubules

Using TIRF, scientists have been able to _________________.

a) compare the properties of different motor proteins
b) measure the properties of individual motors under different experimental conditions
c) ask how a specific mutation of a motor protein affects its motility properties
d) measure the interrelationships between molecular motor subunits
e) compare the properties of different motor proteins, measure the properties of individual motors under different experimental conditions and ask how a specific mutation of a motor protein affects its motility properties

Which technique below can be used to measure the mechanical properties of the cytoskeletal elements themselves?

a) laser beams
b) atomic force microscopy
c) transmission electron microscopy
d) scanning electron microscopy
e) SDS-PAGE

An intermediate filament can stretch up to _____ its normal length before it breaks into two pieces.

a) 1.5
b) 2.5
c) 3.5
d) 10
e) 35

In stretching an intermediate filament with an atomic force microscope, what properties of an intermediate filament can be tested?

a) tensile strength
b) solidity
c) brittleness
d) extensibility
e) tensile strength and extensibility

Which of the following appears to be the most extensible?

a) intermediate filaments
b) microtubules
c) microfilaments
d) spindle fibers
e) microtubules and spindle fibers

A new field of mechanical engineering that involves the development of tiny machines capable of performing specific activities in a submicroscopic world is called ________.

a) nanodictation
b) nanomechanics
c) microscopotechnics
d) nanotechnology
e) picomechanics

In cell biology and with respect to microtubules and microfilaments, the word "dynamic" means ________.

a) impressive
b) constant
c) ever-changing
d) energetic
e) forceful

A microscope is equipped with a laser that can be focused on a small region of the cell. The laser beam is used to bleach fluorescent tubulin in a small region of the cell. The specimen is then followed over time and the recovery of the fluorescent signal into the bleached zone is then measured. What is the name of this technique?

a) TIRF
b) fluorescence recovery after photobleaching
c) total internal refraction microscopy
d) FRAP
e) fluorescence recovery after photobleaching and FRAP

Which of the following could be a method used to label microtubules with a fluorescent dye?

a) injecting tubulin with a fluorescent dye
b) coupling tubulin to a fluorescent dye
c) coupling actin to a fluorescent dye
d) inducing a cell to express the gene for tubulin that has been fused to the gene for GFP
e) coupling tubulin to a fluorescent dye and inducing a cell to express the gene for tubulin that has been fused to the gene for GFP

If the FRAP technique is used to bleach a small zone of fluorescent microtubules in a cell, which of the following is a possible explanation for the recovery of fluorescence in the region of the cell previously bleached?

a) the dynamics of the microtubules turning over in that bleached zone of the cell
b) the growth of new microtubules into the bleached zone
c) movement of microtubules through the bleached zone
d) all of these choices
e) the dynamics of the microtubules turning over in that bleached zone of the cell and the growth of new microtubules into the bleached zone

The microtubule wall is composed of globular proteins arranged in longitudinal rows called _________.

a) microfilaments
b) protofilaments
c) prototubules
d) prototubulins
e) microtubular units

In a normal microtubule, how many protofilaments make up its cylindrical wall?

a) 13
b) 15
c) 11
d) 9
e) 17

What kinds of forces are thought to hold microtubular structure together?

a) strong interactions
b) noncovalent interactions
c) covalent interactions
d) magnetism
e) strong interactions and covalent interactions

An abnormally high level of _______ of the MAP protein tau is implicated in the development of strange, tangled filaments called _________ that have been seen in the brains of patients suffering from several fatal neurodegenerative diseases like Alzheimer's disease.

a) phosphorylation, neurofibrillary tangles
b) phosphorylation, neurofibrillary anastomoses
c) dephosphorylation, neurofibrillary tangles
d) dephosphorylation, neurofibrillary anastomoses
e) amination, neurofibrillary tangles

Given that axons grow out through the action of microtubules, what should happen to axons growing out from a neuron when they are exposed to colchicine or nocodazole?

a) Axons grow more rapidly.
b) Axonal outgrowth stops.
c) Axons grow more rapidly.
d) Axonal outgrowth stops.
e) There is no change in axonal outgrowth.

How are microtubules thought to affect cell shape in plants?

a) Microtubules of the plant cell cortex are thought to affect the movement of cellulose-synthesizing enzymes in the cell membrane, which, in turn, affect cell wall growth and shape.
b) Microtubules of the plant cell vacuole are thought to affect the movement of cellulose-synthesizing enzymes in the cell membrane, which, in turn, affect cell wall growth and shape.
c) Microtubules of the plant cell cortex are thought to affect the movement of lipid-synthesizing enzymes in the cell membrane, which, in turn, affect cell wall growth and shape.
d) Microtubules of the plant cell wall are thought to affect the movement of cellulose-synthesizing enzymes in the cell membrane, which, in turn, affect cell wall growth and shape.

In a growing plant cell, cellulose microfibrils are oriented _______ the direction of cell growth.

a) identically to
b) perpendicular to
c) parallel to
d) diagonal to
e) horizontal to

In what form are proteins and neurotransmitters usually transported down the axon of a nerve cell?

a) individually by diffusion
b) in groups of ten
c) inside transport vesicles
d) inside the Golgi complex
e) tied individually to microtubules

Structures that move from the cell body of a neuron down the axon toward the neuron terminals are said to move in a(n) _________ direction.

a) retrograde
b) anterograde
c) astronomical
d) radial
e) intergrade

The movement of endocytic vesicles formed in the neuron terminals from the synapse to the cell body is said to be in a(n) ________ direction.

a) retrograde
b) anterograde
c) astronomical
d) radial
e) intergrade

Which of the following molecular motors is associated with microfilaments?

a) kinesins
b) dyneins
c) myosins
d) kinesins and dyneins
c) kinesins and myosins

Which of the following molecular motors is known to travel in a retrograde direction along microtubules?

a) kinesins
b) dyneins
c) myosins
d) kinesins and myosins
e) kinesins and dyneins

Which of the following molecular motors is known to travel in an anterograde direction along microtubules?

a) kinesins
b) dyneins
c) myosins
d) kinesins and dyneins
e) kinesins and myosins

What is the direct source of energy that powers molecular motors?

a) hydrolysis of GTP
b) hydrolysis of ATP
c) proton gradient
d) H+ gradient
e) condensation of ATP

What part of the molecular motor kinesin is responsible for binding to the cargo to be hauled?

a) the motor domain
b) the neck
c) the rod-like stalk
d) the fan-shaped tail
e) the motor domain and the neck

Kinesin movement along a microtubule is said to be ________ meaning that it can move long distances along an individual microtubule without falling off.

a) excessive
b) processive
c) depressive
d) progressive
e) egressive

What is the minimum number of kinesin heads in contact with a microtubule at all times?

a) 0
b) 1
c) 2
d) 3
e) 4

The current model for the nucleation of microtubules is that a helical array of gamma-tubulin subunit forms an open, ring-shaped template on which the first row of alphabeta-tubulin dimers assembles. How does this model account for the polarity of microtubules?

a) Only the alpha-tubulin of a heterodimer can bind to the ring of gamma-subunits.
b) Only the beta-tubulin of a heterodimer can bind to the ring of gamma-subunits.
c) The ring structure straightens out the microtubule.
d) The ring structure interacts with a homodimer instead of a heterodimer.
e) Only the alpha-tubulin of a heterodimer can bind to the ring of gamma-subunits. and the ring structure straightens out the microtubule.

Which of the following treatments do not disassemble microtubules in living cells?

a) slightly elevated temperature
b) hydrostatic pressure
c) elevated calcium ion concentration
d) colchicine or vinblastine treatment
e) all of these choices disassemble microtubules in living cells

Why are taxol, vinblastine and other drugs like them used as chemotherapy agents?

a) They preferentially kill tumor cells.
b) They preferentially stabilize tumor cells.
c) They disrupt tumor cell membranes.
d) They prevent entry of cells into the stage of meiosis.
e) They inhibit mitochondria.

Which of the following treatments did not help microtubules to polymerize when homogenates prepared from brain tissue received it?

a) Mg2+ ions
b) GTP
c) EGTA
d) a temperature of 37°C
e) a temperature of 4°C

How does EGTA block microtubule polymerization?

a) It binds Ca2+ ions, which inhibit microtubule polymerization.
b) It binds Mg2+ ions, which inhibit microtubule polymerization.
c) It binds Ca2+ ions, which stabilize microtubule polymerization.
d) It destroys Ca2+ ions, which inhibit microtubule polymerization.
e) It destroys Mg2+ ions, which inhibit microtubule polymerization.

To which end of microtubules are tubulin subunits primarily added in vitro?

a) the minus end
b) the N-terminal end
c) the plus end
d) the C-terminal end
e) the 5'-end

Which of the following is NOT a function of a cilium?

a) moving the cell from place to place
b) moving fluid and particulate material past the cell
c) a role in sensory function in monitoring the properties of extracellular fluids
d) moving vesicles down the nerve cell axon
e) all of these choices are functions of a cilium

The core of a cilium is called the ________.

a) troponeme
b) dynomeme
c) cilioneme
d) axoneme
e) flagelloneme

Which of the following is normally associated with the cilia of organisms from protists to mammals?

a) a 9 + 0 pattern
b) a 9 + 1 pattern
c) a 9 + 2 pattern
d) microtubules
e) none of these choices

Of what protein are the arms attached to the A microtubule of the axoneme composed?

a) tubulin
b) actin
c) dynein
d) keratin
e) myosin

From what structure do cilia and flagella emerge?

a) centromeres
b) basal bodies
c) centrioles
d) spindle
e) MTOC

The peripheral doublets of the axoneme are connected to one another by a(n) ________ composed of an elastic protein _______.

a) intersheath bridge, nexin
b) peridoublet sheath, dynein
c) interdoublet bridge, nexin
d) interdoublet sheath, dynein
e) peridoublet sheath, nexin

What protein is responsible for intraflagellar transport of kinesin-II molecules and recycled axonemal proteins toward the basal body?

a) kinesin-II
b) myosin
c) cytoplasmic dynein
d) kinesin
e) cytoplasmic kinesin

What does treatment of a sperm axoneme with 0.6 M NaCl do to its structure?

a) It removes both arms from the A microtubule.
b) It selectively removes the outer arms from the A microtubule.
c) It selectively removes the inner arms from the A microtubule.
d) It selectively removes the outer arms from the B microtubule.
e) It selectively removes the inner arms from the B microtubule.

The presence of what ion appears to be necessary for connecting the ciliary (axonemal) dynein arms to the A microtubules of the axoneme?

a) calcium
b) potassium
c) magnesium
d) manganese
e) sodium

_______ is an elastic protein that connects tubulin doublets in cilia and flagellae. The resultant bridges play an important role in ciliary and flagellar movement by limiting the extent that adjacent doublets can slide over one another. The resistance to sliding provided by these bridges causes the axoneme to bend.

a) Plectin
b) Filamentin
c) Nexin
d) Vimentin
e) Myosin

The cross-bridges that hold intermediate filaments together are composed of _______.

a) filamentin
b) plectin
c) ascriptin
d) dynein
e) myosin

The central, rod-shaped domain of an intermediate filament is flanked on each side by globular domains of variable size and sequence. What structure forms the core of the central, rod-shaped domain?

a) alpha-helix
b) beta-pleated sheet
c) double helix
d) quaternary coil
e) coiled coil

Which property below is most characteristic of intermediate filaments?

a) elastic
b) highly resistant to shrinkage
c) springy
d) highly resistant to tensile forces
e) hyperflexible

You inject radioactively labeled keratin subunits into cultured skin cells. What happens a few minutes later?

a) The keratin subunits remain in the cytoplasmic keratin subunit pool.
b) Filaments initially become labeled at scattered sites along their length.
c) Filaments become labeled at both ends simultaneously.
d) Filaments become labeled at one end exclusively.
e) The entire intermediate filament network is quickly labeled.

Which protein below is often a component of intermediate filaments?

a) alpha-tubulin
b) beta-tubulin
c) actin
d) keratin
e) myosin

What seems to control the assembly and disassembly of intermediate filaments?

a) denaturation
b) sulfation
c) phosphorylation and dephosphorylation
d) hydrolysis
e) hydroxylation

With which of the following structures are intermediate filaments associated?

a) the nuclear envelope in the center of the cell
b) hemidesmosomes
c) desmosomes
d) the neurofilaments of neuron axons
e) all of these choices

What kind of cells seem to rely mostly on microfilaments for long-distance transport of cytoplasmic vesicles and organelles, probably due to the restricted microtubule distribution in these cells?

a) red blood cells
b) white blood cells
c) plant cells
d) neurons
e) muscle cells

Which of the following words best describes the structure of an actin filament?

a) single actin strand
b) triple helix
c) hyperpolar filament
d) double helix
e) supercoil

Which of the following does not describe the types of microfilament organization normally seen in cells?

a) highly ordered arrays
b) loose, ill-defined networks
c) tightly anchored bundles
d) cylindrical conglomerations
e) all of these choices describe types of microfilament organization

What chemical below is known to free actin monomers and block their incorporation into the polymer?

a) cytochalasins
b) nocodazole
c) phalloidin
d) latrunculin
e) phalloidin and latrunculin

What motor is associated with microfilaments?

a) myoglobin
b) kinesin
c) myosin
d) dynein
e) myometrium

Where does the energy to run myosin motors come from?

a) GTP
b) ATP
c) proton gradient
d) CTP
e) creatine phosphate

The myosin filament is characterized as a(n) _________ filament.

a) bipolar
b) unipolar
c) tripolar
d) parallel
e) orthogonal

A culture of Dictyostelium slime mold is prepared in which the myosin II gene is deleted. In which activity or activities below are these cells unable to participate?

a) separation of chromosomes during mitosis
b) cell elongation
c) cytokinesis
d) separation of chromosomes during mitosis and cell elongation
e) separation of chromosomes during mitosis and cytokinesis

Why is myosin V able to take very large steps along a microfilament?

a) Its neck is twisted.
b) Its neck is relatively long.
c) Its neck is relatively short.
d) Its tail is very long.
e) Its tail is bipolar.

Along which structure do membranous vesicles and organelles typically move long distances in an animal cell?

a) mitochondria
b) microtubules
c) microfilaments
d) intermediate filaments
e) lysosomesb) microtubules

Along which structure do membranous vesicles and organelles typically engage in local movement in the cell periphery of an animal cell?

a) mitochondria
b) microtubules
c) microfilaments
d) intermediate filaments
e) lysosomes

How do muscle cells become multinucleate?

a) They undergo fission.
b) They become multinucleate via the embryonic fusion of large numbers of mononucleate myoblasts.
c) They become multinucleate via the embryonic fusion of large numbers of multinucleate myoblasts.
d) They become multinucleate via mitosis in myoblasts without cytokinesis.
e) They become multinucleate via the embryonic fusion of mononucleaate neuroblasts.

Myofibrils in a muscle cell are made up of a repeating linear array of contractile units called ________.

a) sarcocytes
b) blastomeres
c) myomeres
d) sarcomeres
e) myotubules

What is the name of the lightly staining areas at the outer edges of a sarcomere?

a) A bands
b) H zones
c) I bands
d) Z lines
e) M lines

What is the name of the densely staining area between the lightly staining areas at the outer edges of a sarcomere?

a) A bands
b) H zones
c) I bands
d) Z lines
e) M lines

Which region of the sarcomere contains only actin thin filaments or microfilaments?

a) A bands
b) H zones
c) I bands
d) Z lines
e) M lines

Which region of the sarcomere represents the region of overlap between the two types of filaments in the sarcomere?

a) A bands
b) the part of the A band on either side of the H zone
c) I bands
d) Z lines
e) the part of the H zone on either side of the A band

What accounts for the decrease in the length of an entire muscle?

a) the combined decrease in sarcomere length
b) the combined shortening of actin filaments
c) the combined shortening myosin filaments
d) the combined shortening of thin filaments
e) the combined decrease in sarcomere length and the combined shortening of actin filaments

Which of the following would be an accurate title for a movie about the mechanism of muscle contraction?

a) Sliding Lamina
b) Shortening Filaments
c) Sliding Filaments
d) And Then There Were Two
e) Filaments At Large

What links actin filament barbed ends to the Z line?

a) troponin
b) myosin
c) actinin
d) titin
e) tropomyosin

What is the name of the largest protein yet discovered? It extends from the M line in the center of the sarcomere along the myosin filament and past the A band to terminate at the Z line.

a) troponin
b) myosin
c) actinin
d) titin
e) tropomyosin

Why does an actin thin filament manage to move continuously during a contraction cycle?

a) All of the myosin heads beat synchronously.
b) All of the myosin heads beat out of synchrony with one another.
c) They use an enormous amount of ATP.
d) They use an enormous amount of GTP.
e) none of these choices

A(n) ________ motor, like muscle myosin (myosin II) and unlike myosin V, remains in contact with its track, in this case the thin filament, for only a small portion, less than 5 percent, of the overall cycle.

a) processive
b) nonprocessive
c) efficient
d) small
e) large

What provides the energy that drives sarcomere contraction?

a) ATP
b) ADP
c) GTP
d) GDP
e) none of these choices

The point at which the neuron axon terminus and the muscle fiber make contact is called the _________.

a) neuromuscular terminus
b) nerve exons
c) neural conjunctions
d) neuromuscular junction
e) neuromuscular conjunction

What blocks the myosin-binding sites on actin thin filaments in a stimulated sarcomere?

a) troponin
b) myosin itself
c) tropomyosin
d) titin
e) nothing

What is a major influence in determining the organization and behavior of actin filaments inside cells?

a) actinin-binding proteins
b) tubulin
c) actin-binding proteins
d) dynein
e) actin-binding proteins and dynein

Proteins that accelerate the polymerization of actin filaments are called ________.

a) nucleons
b) nucleating proteins
c) monomer-sequestering proteins
d) end-blocking proteins
e) nucleons and nucleating proteins

_______ proteins share considerable sequence homology with actins and accelerate the polymerization of actin filaments.

a) Actin-nucleating
b) Actin-racemase
c) Actin-related
d) Tubulin-related
e) Actin-rated

A shift in the concentration or activity of which type of proteins can cause a shift in the equilibrium between actin monomers and polymers?

a) nucleating proteins
b) monomer-sequestering proteins
c) endolysins
d) capping proteins
e) all of these choices

________ proteins are able to alter the three-dimensional organization of an actin filament population.

a) Monomer-polymerizing
b) Cross-linking
c) Filament-severing
d) Actin-filament depolymerizing
e) End-blocking

Which type of actin-binding protein is known to decrease cytoplasmic viscosity by breaking existing actin filaments into two or more pieces?

a) monomer-polymerizing proteins
b) cross-linking proteins
c) filament-severing proteins
d) actin-filament depolymerizing proteins
e) end-blocking proteins

Which of the following nonmuscle cell activities do not involve actin filaments often working in concert with myosin motors?

a) cytokinesis
b) blood platelet activation
c) vesicle trafficking
d) red blood cells carrying oxygen
e) changes in cell shape

As a fibroblast moves, its leading edge extends from the cell as a broad, flattened, veil-like protrusion called a ________.

a) pseudopodium
b) lamella
c) lamellipodium
d) podium
e) extensor

One of the WASP/WAVE family of proteins, specifically WASP, the founding member of the family, is associated with what disease below?

a) hemophilia
b) Wiskott-Aldrich syndrome
c) lymphoma
d) lupus erythematosus
e) Wallace's syndrome

If you were to fix a fish keratocyte and stain it with fluorescent antibodies for myosin II, where would you see the myosin II?

a) in the advancing lamellipodium edge
b) in the rear of the cell
c) in a band where the rear of the lamellipodium joins the rest of the cell
d) around the nucleus
e) surrounding the mitochondria

The focal complexes that form near the leading edge of a motile cell exert traction force through their associated __________ and then typically disassemble as the cell moves forward.

a) microtubules
b) keratin filaments
c) vinculin filaments
d) actin filaments
e) actinin filaments