Which of the following statements about the cytoskeleton is false?
(a) The cytoskeleton is made up of three types of protein filaments.
(b) The cytoskeleton controls the location of organelles in eukaryotic cells.
(c) Covalent bonds between protein monomers hold together cytoskeletal
filaments.
(d) The cytoskeleton of a cell can change in response to the environment.
answer
c
question
Which of the following statements about the cytoskeleton is true?
(a) All eukaryotic cells have actin, microtubules, and intermediate filaments
in their cytoplasm.
(b) The cytoskeleton provides a rigid and unchangeable structure important
for the shape of the cell.
(c) The three cytoskeletal filaments perform distinct tasks in the cell and act
completely independently of one another.
(d) Actin filaments and microtubules have an inherent polarity, with a plus
end that grows more quickly than the minus end.
answer
d
question
Which of the statements below about intermediate filaments is false?
(a) They can stay intact in cells treated with concentrated salt solutions.
(b) They can be found in the cytoplasm and the nucleus.
(c) They can be anchored to the plasma membrane at a cell-cell junction.
(d) Each filament is about 10 µm in diameter
answer
d
question
All intermediate filaments are of similar diameter because ____________.
(a) the central rod domains are similar in size and amino acid sequence.
(b) the globular domains are similar in size and amino acid sequence.
(c) covalent bonds among tetramers allow them to pack together in a similar
fashion.
(d) there is only a single type of intermediate filament in every organism.
answer
a
question
Intermediate filaments help protect animal cells from mechanical stress because
____________.
(a) filaments directly extend from the interior of the cell to the extracellular
space and into the next cell, linking one cell to the next, helping to
distribute locally applied forces.
(b) filaments in each cell are indirectly connected to the filaments of a
neighboring cell through the desmosome, creating a continuous
mechanical link between cells.
(c) filaments remain independent of other cytoskeletal elements and keep the
mechanical stress away from other cellular components.
(d) filaments make up the desmosome junctions that connect cells; these
junctions are more important than the internal network of filaments for
protecting cells against mechanical stress.
answer
b
question
Intermediate filaments are made from elongated fibrous proteins that are
assembled into a ropelike structure. Figure Q17-10 shows the structure of an
intermediate filament subunit. You are interested in how intermediate filaments
are formed, and you create an intermediate filament subunit whose α-helical
region is twice as long as that of a normal intermediate filament by duplicating the
normal α-helical region while keeping a globular head at the N-terminus and a
globular tail at the C-terminus; you call this subunit IFαd. If you were to assemble
intermediate filaments using IFαd as the subunit, which of the following
predictions describes the most likely outcome?
Figure Q17-10
(a) Filaments assembled using IFαd will interact with different cytoskeletal
components.
(b) Filaments assembled using IFαd will form dimers that are twice as long as
dimers assembled from normal intermediate filaments.
(c) Sixteen tetramers assembled from IFαd will be needed for a ropelike
structure to form.
(d) Dimers of IFαd will form by interactions with the N-terminal globular
head and the C-terminal globular tail.
answer
b
question
Match the type of intermediate filament with its appropriate location.
lamins______________
neurofilaments____________
vimentins______________
keratins___________
A. nerve cells
B. epithelia
C. nucleus
D. connective tissue
answer
CADB
question
Keratins, neurofilaments, and vimentins are all categories of intermediate
filaments. Which of the following properties is not true of these types of
intermediate filaments?
(a) They strengthen cells against mechanical stress.
(b) Dimers associate by noncovalent bonding to form a tetramer.
(c) They are found in the cytoplasm.
(d) Phosphorylation causes disassembly during every mitotic cycle.
answer
d
question
You are studying nuclear lamins in yeast. Using recombinant DNA technology,
you alter the coding sequence of a nuclear lamin gene such that the gene now
codes for a nuclear lamin protein that can no longer be phosphorylated when the
nuclear envelope is broken down during mitosis. What do you predict would
happen if the yeast cell only had the altered nuclear lamin gene (and not the
unaltered version)?
(a) Mitosis should proceed as usual because the dephosphorylation of the
lamin is what is important for nuclear lamina assembly during mitosis, so
phosphorylation will not be necessary.
(b) Disassembly of the nuclear lamins will occur prematurely because the
lamins cannot be phosphorylated.
(c) Nuclear lamins will no longer disassemble properly during mitosis.
(d) Nuclear lamins will be unable to produce dimers, as coiled-coil formation
will be disrupted
answer
c
question
You are interested in understanding the regulation of nuclear lamina assembly. To
create an in vitro system for studying this process you start with partly purified
nuclear lamina subunits to which you will add back purified cellular components
to drive nuclear lamina assembly. Before you start doing experiments, your
instructor suggests that you consider what type of conditions would be most
amenable to the assembly of the nuclear lamina from its individual subunits in
vitro. Which of the following conditions do you predict would be most likely to
enhance the assembly of the nuclear lamina?
(a) addition of phosphatase inhibitors
(b) addition of ATP
(c) addition of a concentrated salt solution that is 10 times the concentration
normally found in the nucleoplasm
(d) addition of protein kinase inhibitors
answer
d
question
Which of the following statements about the structure of microtubules is false?
(a) Microtubules are built from protofilaments that come together to make a
hollow structure.
(b) The two ends of a protofilament are chemically distinct, with α-tubulin
exposed at one end and β-tubulin exposed at the other end.
(c) Within a microtubule, all protofilaments are arranged in the same
orientation, giving the microtubule structural polarity.
(d) α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer
that then assembles into protofilaments
answer
d
question
Which of the following statements about the function of the centrosome is false?
(a) Microtubules emanating from the centrosome have alternating polarity
such that some have their plus end attached to the centrosome while others
have their minus end attached to the centrosome.
(b) Centrosomes contain hundreds of copies of the γ-tubulin ring complex
important for microtubule nucleation.
(c) Centrosomes typically contain a pair of centrioles, which is made up of a
cylindrical array of short microtubules.
(d) Centrosomes are the major microtubule-organizing center in animal cells.
answer
a
question
Which of the following statements about microtubules is true?
(a) Motor proteins move in a directional fashion along microtubules by using
the inherent structural polarity of a protofilament.
(b) The centromere nucleates the microtubules of the mitotic spindle.
(c) Because microtubules are subject to dynamic instability, they are used
only for transient structures in a cell.
(d) ATP hydrolysis by a tubulin heterodimer is important for controlling the
growth of a microtubule.
answer
a
question
The hydrolysis of GTP to GDP carried out by tubulin molecules
________________.
(a) provides the energy needed for tubulin to polymerize.
(b) occurs because the pool of free GDP has run out.
(c) tips the balance in favor of microtubule assembly.
(d) allows the behavior of microtubules called dynamic instability
answer
d
question
The microtubules in a cell form a structural framework that can have all the
following functions except which one?
(a) holding internal organelles such as the Golgi apparatus in particular
positions in the cell
(b) creating long, thin cytoplasmic extensions that protrude from one side of
the cell
(c) strengthening the plasma membrane
(d) moving materials from one place to another inside a cell
answer
c
question
You discover a protein, MtA, and find that it binds to the plus ends of
microtubules in cells. The hypothesis that best explains this localization is
________________.
(a) MtA is involved in stabilizing microtubules.
(b) MtA binds to GTP-bound tubulin on microtubules.
(c) MtA is important for the interaction of microtubules with the centrosome.
(d) MtA will not bind to purified microtubules in a test tube.
answer
b
question
Which of the following statements regarding dynamic instability is false?
(a) Each microtubule filament grows and shrinks independently of its
neighbors.
(b) The GTP cap helps protect a growing microtubule from depolymerization.
(c) GTP hydrolysis by the tubulin dimer promotes microtubule shrinking.
(d) The newly freed tubulin dimers from a shrinking microtubule can be
immediately captured by growing microtubules and added to their plus
end.
answer
d
question
Which of the situations below will enhance microtubule shrinkage?
(a) addition of a drug that inhibits GTP exchange on free tubulin dimers
(b) addition of a drug that inhibits hydrolysis of the GTP carried by tubulin
dimers
(c) addition of a drug that increases the affinity of tubulin molecules carrying
GDP for other tubulin molecules
(d) addition of a drug that blocks the ability of a tubulin dimer to bind to γ-
tubulin
answer
a
question
The graph in Figure Q17-31 shows the time course of the polymerization of pure
tubulin in vitro. Assume that the starting concentration of free tubulin is higher
than it is in cells.
Figure Q17-31
Three parts of the curve are labeled above it as A, B, and C. You conduct a
similar in vitro tubulin-polymerization experiment, only you include purified
centrosomes in your preparation. When you plot your data, which part of your
graph should be most dissimilar to the curve shown in Figure Q17-31?
(a) A
(b) B
(c) C
(d) None. The shape of my graph should be identical to the graph produced
when tubulin is polymerized in the absence of purified centrosomes
answer
a
question
Which of the following statements about organellar movement in the cell is false?
(a) Organelles undergo saltatory movement in the cell.
(b) Only the microtubule cytoskeleton is involved in organellar movement.
(c) Motor proteins involved in organellar movement use ATP hydrolysis for
energy.
(d) Organelles are attached to the tail domain of motor proteins.
answer
b
question
Microtubules are important for transporting cargo in nerve cell axons, as
diagrammed in Figure Q17-33. Notice that the two types of cargo are traveling in
opposite directions. Which of the following statements is likely to be false?
Figure Q17-33
(a) The gray cargo is attached to dynein.
(b) The black cargo and the gray cargo require ATP hydrolysis for their
motion.
(c) The black cargo moving toward the axon terminal contains a domain that
specifically interacts with the tail domain of a particular kind of motor.
(d) The black cargo and the gray cargo are moving along microtubules of
opposite polarity.
answer
d
question
Which of the following statements is correct? Kinesins and dyneins
____________________.
(a) have tails that bind to the filaments.
(b) move along both microtubules and actin filaments.
(c) often move in opposite directions to each other.
(d) derive their energy from GTP hydrolysis.
answer
c
question
Which of the following items is not important for flagellar movement?
(a) sarcoplasmic reticulum
(b) ATP
(c) dynein
(d) microtubules
answer
a
question
Figure Q17-40A shows how the movement of dynein causes the flagellum to
bend. If instead of the normal situation, the polarity of the adjacent doublet of
microtubules were to be reversed (see Figure Q17-40B), what do you predict
would happen?
Figure Q17-40
(a) No bending would occur.
(b) Bending would occur exactly as diagrammed in Figure Q17-40A.
(c) Bending would occur, except that the right microtubule doublet would
move down relative to the left one.
(d) The two microtubule doublets would slide away from each other
answer
c
question
Which of the following statements about actin is false?
(a) ATP hydrolysis decreases actin filament stability.
(b) Actin at the cell cortex helps govern the shape of the plasma membrane.
(c) Actin filaments are nucleated at the side of existing actin filaments in
lamellipodia.
(d) The dynamic instability of actin filaments is important for cell movement.
answer
d
question
Consider the mechanism by which actin and tubulin polymerize. Which of the
items below does not describe something similar about the polymerization
mechanisms of actin and microtubules?
(a) Although both filaments can grow from both ends, the growth rate is faster
at the plus ends.
(b) Depolymerization initiates at the plus ends of filaments.
(c) Nucleotide hydrolysis promotes depolymerization of filaments.
(d) Free subunits (actin and tubulin) carry nucleoside triphosphates.
answer
b
question
For both actin and microtubule polymerization, nucleotide hydrolysis is important
for ______.
(a) stabilizing the filaments once they are formed.
(b) increasing the rate at which subunits are added to the filaments.
(c) promoting nucleation of filaments.
(d) decreasing the binding strength between subunits on filaments.
answer
d
question
Compared to the normal situation, in which actin monomers carry ATP, what do
you predict would happen if actin monomers that bind a nonhydrolyzable form of
ATP were incorporated into actin filaments?
(a) Actin filaments would grow longer.
(b) Actin filaments would grow shorter because depolymerization would be
enhanced.
(c) Actin filaments would grow shorter because new monomers could not be
added to the filaments.
(d) No change, as addition of monomers binding nonhydrolyzable ATP would
not affect actin filament length.
answer
a
question
Which of the following statements is false?
(a) Cytochalasins prevent actin polymerization.
(b) Actin filaments are usually excluded from the cell cortex.
(c) Integrins are transmembrane proteins that can bind to the extracellular
matrix.
(d) ARPs can promote the formation of branched actin filaments
answer
b
question
Cell movement involves the coordination of many events in the cell. Which of the
following phenomena is not required for cell motility?
(a) Myosin-mediated contraction at the rear of the moving cell.
(b) Integrin association with the extracellular environment.
(c) Nucleation of new actin filaments.
(d) Release of Ca2+ from the sarcoplasmic reticulum.
answer
d
question
Figure Q17-52 shows the leading edge of a lamellipodium. Which of the
following statements is false?
Figure Q17-52
(a) Nucleation of new filaments near the leading edge pushes the plasma
membrane forward.
(b) ARP proteins nucleate the branched actin filaments in the lamellipodium.
(c) Capping proteins bind to the minus end of actin filaments.
(d) There is more ATP-bound actin at the leading edge than in the actin
filaments away from the leading edge.
answer
c
question
You are examining a cell line in which activation of the Rho family member Rac
promotes lamellipodia formation. Which of the following statements is most
likely to be true?
(a) Cells carrying a Rac mutation that makes Rac act as if it is always bound
to GTP will polymerize more unbranched actin filaments than normal
cells.
(b) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for
GTP will polymerize more unbranched actin filaments than normal cells.
(c) Cells carrying a Rac mutation that makes Rac act as if it is always bound
to GTP will polymerize more branched actin filaments than normal cells.
(d) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for
GTP will polymerize more branched actin filaments than normal cells.
answer
c
question
In the budding yeast, activation of the GTP-binding protein Cdc42 occurs on
binding of an external signal (pheromone) to a G-protein-coupled receptor.
Activation of Cdc42 promotes actin polymerization. Predict what would happen
to actin polymerization, in comparison with pheromone-treated cells, in the
following cases.
A. You add pheromone to an inhibitor of G-protein-coupled receptors.
B. You add pheromone to a nonhydrolyzable analog of GTP.
answer
A. Less actin polymerization
B. More actin polymerization
question
Your friend works in a biotech company that has just discovered a drug that
seems to promote lamellipodia formation in cells. Which of the following
molecules is unlikely to be involved in the pathway that this drug affects?
(a) Rac
(b) ARP
(c) actin
(d) myosin
answer
d
question
Which of the following structures shorten during muscle contraction?
(a) myosin filaments
(b) flagella
(c) sarcomeres
(d) actin filaments
answer
c
question
Figure Q17-57shows an electron micrograph of a skeletal muscle fiber, where
various points along a fiber and various regions have been labeled.
Figure Q17-57
Which of the following statements is true about muscle contraction?
(a) Point A will move closer to point B.
(b) Point B will move closer to point C.
(c) Region D will become smaller.
(d) Region E will shrink in size.
answer
b
question
Which of the following conditions is likely to decrease the likelihood of skeletal
muscle contraction?
(a) partial depolarization of the T-tubule membrane, such that the resting
potential is closer to zero
(b) addition of a drug that blocks Ca2+ binding to troponin
(c) an increase in the amount of ATP in the cell
(d) a mutation in tropomyosin that decreases its affinity for the actin filament
answer
b
question
Which of the following statements about skeletal muscle contraction is false?
(a) When a muscle cell receives a signal from the nervous system, voltagegated
channels open in the T-tubule membrane.
(b) The changes in voltage across the plasma membrane that occur when a
muscle cell receives a signal from the nervous system cause an influx of
Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction.
(c) A change in the conformation of troponin leads to changes in tropomyosin
such that it no longer blocks the binding of myosin heads to the actin
filament.
(d) During muscle contraction, the Z discs move closer together as the myosin
heads walk toward the plus ends of the actin filaments.
answer
b
question
Consider the in vitro motility assay using purified kinesin and purified
polymerized microtubules shown in Figure Q17-63. The three panels are images
taken at 1-second intervals. In this figure, three microtubules have been numbered
to make it easy to identify them. Which of the following statements about this
assay is false?
Figure Q17-63
(a) Kinesin molecules are attached by their tails to a glass slide.
(b) The microtubules used in this assay must be polymerized using conditions
that stabilize tubule formation or else they would undergo dynamic
instability.
(c) ATP must be added for this assay to work.
(d) Addition of the nonhydrolyzable ATP analog (AMP-PNP) would cause
the microtubules to move faster.
answer
d
Haven't found what you need?
Search for quizzes and test answers now
Quizzes.studymoose.com uses cookies. By continuing you agree to our cookie policy