Cytoskeleton Flashcards
What are the functions of the cystoskeleton?
A) Structual integrity
B) Cell motility
C) Contraction
D) Organization
E) All of the above
E
Which are the thickest filaments?
A) Microtubules
B) Cytoskeleton
C) Actin filaments
D) intermediate filaments
A
Pairs form stable polar dimers via coiled-coils , with head to
head and tail to tail
A) IF
B) Actin
C) Centerometers
D) MT
A)
General properties of IF
A) provide tensile strength
B) Network surrounds nucleus and
extends throughout cytoplasm in
animal cells
C)Form nuclear lamina in all eukaryotes.
D. Contribute to cell-cell junctions at
desmosomes.
E) A, B, C, and D
E
Two dimers associate side-to-side to form a staggered
tetramer, resulting in a structure that is the same on
both ends. What is the polarity of the tetramers
A) Polar
B) non covalent polar
C) nonpolar
D) covalent polar
C
Which of the following is the smallest nonpolar assembly (one
end is no different from the other end)?
A. The intermediate filament dimer
B. The intermediate filament tetramer
C. The lateral association of 8 tetramers
D. The fully assembled intermediate filament
E. None of the above (A, B, C or D) is polar
B
What does the Lamin of IFs form?
Nuclear lamina
IFs provide strength to withstand mechanical
stress (resistance to stretching; tensile
strength) via what?
A) IF
B) MT
C) Sheets
D) desmosome
D
Why does the cell rupture between the nucleus of mice which leads to blitsering skin
Keratin mutant
What is Pectin and why is important to IFS?
Plectins stabilize and reinforce network by bundling IFs.
-Connect to the other cytoskeletal networks and desmosomes.
-Interlinking with accessory proteins is not required for filament
formation but is required for function: Plectin minus mice die
after birth.
IF
What causes progeria (“premature aging”) ?
Phosphorylation results in
weakened binding between tetramers, due to disassembly of Lamins
Four classes of IFs
Keratins, Vimentin, neurofilaments, nuclear Lamins
Assembly
controlled by
phosphorylation?
Nuclear Lamins
Intermediate filaments help protect animal cells from mechanical stress
because filaments
A.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. remain independent of other cytoskeletal elements and keep the mechanical
stress away from other cellular components.
C.in each cell are indirectly connected to the filaments of a neighboring cell
through the desmosome, creating a continuous mechanical link between
cells.
D.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.
C
Microtubles
- Rapid assembly and disassembly
- Organization
-hollow tubes formed by dimers; thickest
cytoskeletal element.
-emanate from a Microtubule-organizing Centers
(MTOC) such as centrosomes and basal bodies. - Form stable structures which are a railroad system
for propulsion of cellular components via
interactions with motor proteins. - Form cilia and flagella
What is the structure polarity of MTs?
Alpha (-), Beta (+), dimers stacks to form protofilaments
How many protofilaments of MT form a hollow tube?
A)10
B)15
C)13
D) 12
C
How many centrioles are in the centrioles in most animal cells ?
Two
MTOC of yeast and budding yeast
A) 3
B)1
C) 4
D) 0
B
HOW many MTOC of Plant cell and intestinal epithelial cell?
Many
Consider a solution that contains some microtubules as well as some
unassembled alpha/beta tubulin heterodimers. What would happen if you add a
solution that contains only GDP and no GTP?
A. The microtubules will exhibit dynamic instability – sometimes growing,
sometimes shrinking.
B. The microtubules will shrink until all tubulin heterodimers are in the
unassembled state.
C. The microtubules will stop growing but will not shrink either.
D. The microtubules will continue to grow until all free tubulin subunits have
been used up.
E. None of the above (A, B, C or D) is the correct answer.
B
Taxol are antimitotic and anti cancer drugs they..
A) Form complx with tubulin dimers that bind to the end of a mt, preventing further polymerization
B) Bind to filaments and prevent depolymerization
C) Binds tubulin dimers and prevents polymerization
D) A, B, C
B
Colchicine are antimitotic and anti cancer drugs they
A) Form complx with tubulin dimers that bind to the end of a mt, preventing further polymerization
B) Bind to filaments and prevent depolymerization
C) Binds tubulin dimers and prevents polymerization
D) A, B, C
A
Nocodazole are antimitotic and anti cancer drugs they
A) Form complx with tubulin dimers that bind to the end of a mt, preventing further polymerization
B) Bind to filaments and prevent depolymerization
C) Binds tubulin dimers and prevents polymerization
D) A, B, C
C)
Dyneins move toward the
minus end
Two types of MT motor proteins
Kinesins move toward the
Plus end
What cargoes move along MTs?
Membrane enclosed organales, vesicles, and indivudual proteins
Dimers with two globular head domains extract energy from
_________ to power conformational changes that move
the protein relative to the filament. Two heads so one can
hold on while other releases its grip and moves forward
ATP hydrolysis
You attach kinesin molecules by their tails at random
orientations to a glass slide, and then add stably assembled
microtubules to the glass slide. What will happen?
A. The microtubules will not move
B. The microtubules will move back and forth, first in one
direction and then in the opposite direction.
C. Some microtubules will be severed somewhere in the middle,
as dynein motors motors pull them in opposite directions.
D. The microtubules will move in the direction of their + ends (+
ends move further in the + direction)
E. The microtubules will move in the direction of their – ends (-
ends move further in the – direction)
E
Structure: MTs arranged in a ___ array
A) 9+3
B)3+5
C)9+1
D) 9+2
D
Which of the following proteins is NOT a component of
a cilium or flagellum?
A. doublet microtubules
B. kinesins
C. radial spoke proteins
D. linking proteins between microtubules
E. the plasma membrane
B
How many doublets in outer ring of MTs
A) 6
B) 9
C) 8
D) 2
B
Outer ring and central pair are linked by ___and ______, and there are dynein motors that generate the
movements
“spokes” and
“rim”
The AF is inherently unstable and can disassemble from
the - end; ____ stabilizes, ____ produced by hydrolysis
after assembly destabilizes
ATP, ADP
Structural polarity of AFs
Identical subunits interact
to form a strand in which all
subunits point in the same
direction: polarity.
b. Filament is a two-stranded
helix
– Twists every 37 nm
– Held together by very
strong noncovalent
interactions
c. Filaments are thin and
flexible
d. Usually cross-linked into
bundles with other
filaments
Fig 17-30
in vitro, actin filaments can grow at either end, but the +
end is faster and tend to shrink at ____ end
A) plus
B) plus and Minus end
C) minus end
D) ADP
C
These drugs freeze cell movements
because assembly and disassembly
are both required.
A) Phalloidin
B) Cytochalasin
C) Latrunculin
D) all of the above
D
Phalloidin does what ?
A) Binds filaments and prevents depolymerization
B) Binds actin monomers and prevents their polymerization
C) Caps filament plus end, preventing polyerization and leading to filament depolymerization at minus ends
A
Laturnculin does what ?
A) Binds filaments and prevents depolymerization
B) Binds actin monomers and prevents their polymerization
C) Caps filament plus end, preventing polyerization and leading to filament depolymerization at minus ends
C
Cytochalasin does what ?
A) Binds filaments and prevents depolymerization
B) Binds actin monomers and prevents their polymerization
C) Caps filament plus end, preventing polyerization and leading to filament depolymerization at minus ends
B
Thymosin profilin
A) monomer squeezing protein
B) Motor protein
C) cross linking protein
D severing protein
A
Gelsolin does what
Breaks
Lamellipodia are a sheetlike
leading edge with a dense
meshwork of _____ filaments -
Plus ends close to ______
Actin, plasma
membrane
Filopdia are thin, stiff
protrusions formed by _______ of filaments. Plus
end close to _____
loose
bundle, membrane
What are the three main steps to crawling ?
to nucleate new filament.
Plus ends are protected by
capping proteins
Minus ends continuously
disassemble from – end
and grow on + end to
move lamellipodia
forward. Fig 17-36
-Three main steps to crawling…
* Step 1: ProtrusionARPs promote formation of
branched filaments.
Attach to side of filament
to nucleate new filament.
Plus ends are protected by
capping proteins
Minus ends continuously
disassemble from – end
and grow on + end to
move lamellipodia
Step 2: adhesion. Stick to favorable surfaces because
transmembrane proteins (integrins) link extracellular molecules to
actin network.
* Step 3: contraction to bring the rear of the cell along; involves
myosin motor proteins.
Fig 17-34
Myosin I (one head domain) in
_______ types.
Myosin II (two head domains in
a dimer) in _______types also.
All cell, muscle and other
cell
What triggers formation of lamellipodia?
A) Cdc42
B) Rho
C) Rac
C
What triggers polymerization to form filopodia?
A) Cdc42
B) Rho
C) Rac
A)
Sarcomere is
contractile unit.
___ ends of actin
filaments are
anchored at Z disc.
-Actin and myosin
filaments overlap
PLus ends
No bound nucleotide or phosphate
Myosin locked onto actin
A) Released
B) Attactched
C) Cocked
D) Rebinding and power stroke
B
Myosin binds ATP
Releases actin
A) Released
B) Attactched
C) Cocked
D) Rebinding and power stroke
A
Myosin hydrolyses ATP to ADP and Pi
Causes conformational change that
moves myosin head forward
A) Released
B) Attactched
C) Cocked
D) Rebinding and power stroke
C
Intermediate filaments are formed from
A. globular subunits that assemble to form two-stranded helices, with all the subunits pointing in the same
direction in both of the strands.
B. globular subunits that assemble to form two-stranded helices, with all the subunits in one strand pointing
in the opposite direction to those in the other strand.
C. large assemblies of trimers, where each trimer is a triple helical structure.
D. assembly of tubulin dimers.
E. further assembly of two polypeptides with -helical central domains that coil around each other in
a coiled-coil structure to form dimers.
E
Which of the following is the SMALLEST assembly unit of an intermediate filament that LACKs
polarity (one end is no different from the other end)?
A. The intermediate filament monomer
B. The intermediate filament dimer
C. The intermediate filament tetramer
D. The lateral association of 8 tetramers
E. The fully assembled intermediate filament
C
Progeria, a disease with symptoms the resemble premature aging, is caused by mutations in genes
encoding which protein?
A. Keratins
B. Lamins
C. Vimentin
D. Neurofilaments
E. Plectins
B
What type of protein is typically exposed at the POSITIVE (+) end of a growing microtubule?
A. tubulin
B. tubulin
C. tubulin
D. centriolin
E. None of the above (A, B, C or D) is exposed at the positive end
B
Consider a solution that contains some microtubules as well as some unassembled alpha/beta tubulin
heterodimers. What would happen if you add a solution that contains no GTP or GDP but only a high
concentration of an analog that is similar to GTP and can be bound instead of GTP by the heterodimer,
but cannot be hydrolyzed?
A. The microtubules will exhibit dynamic instability – sometimes growing, sometimes shrinking.
B. The microtubules will shrink until all tubulin heterodimers are in the unassembled state.
C. The microtubules will stop growing but will not shrink either.
D. The microtubules will continue to grow until all free tubulin subunits have been used up.
F. None of the above (A, B, C or D) is the correct answer.
D
You attach dynein molecules by their tails at random orientations to a glass slide, and then add stably
assembled microtubules to the glass slide. What will happen?
A. The microtubules will not move.
B. The microtubules will move back and forth, first in one direction and then in the opposite direction.
C. Some microtubules will be severed somewhere in the middle, as dynein motors pull them in opposite
directions.
D. The microtubules will move in the direction of their – ends (- ends move further in the – direction).
E. The microtubules will move in the direction of their + ends (+ ends move further in the +
direction).
E
Which of the following proteins is NOT a component of a cilium or flagellum?
A. doublet microtubules
B. kinesins
C. radial spoke proteins
D. linking proteins between microtubules
E. the plasma membrane
B
Actin filaments
A. are assembled from a two different types of monomers (alpha and beta) in a single strand of the
filament, and filaments are formed from helices of two strands.
B. are assembled from a single type of monomer that all point in the same direction in a single
strand of the filament, and filaments are formed from helices of two strands.
C. are assembled from a single type of monomer in a single strand of the filament that has no polarity, and
filaments are formed from helices of two strands.
D. are assembled from a two different types of monomers (alpha and beta) in a single strand, and filaments
consist of single strands.
E. are assembled from a single type of monomer that all point in the same direction in a single strand, and
filaments are formed from a single strand
B
Which of the following proteins can cause actin filaments to extend from their positive end or to form
at a branch?
A. formins
B. actin-related proteins (ARPs)
C. profilins
D. B and C are both correct.
E. A and B are both correct.
E
As fibroblasts move across a surface, actin filaments
A. are extended at their positive ends to generate protrusions.
B. interact with myosin at the trailing side of the cell to contract this part of the cell.
C. interact at focal adhesion sites with integrins, which also tether the cell to the extracellular matrix.
D. A and B are both correct but not C.
E. A, B and C are all correct
E
Rearrangement of actin filaments in cells can be triggered via cell surface receptors signaling through
A. Myosins.
B. Pofilins.
C. The Rho protein family of GTP-binding proteins.
D. Thymosin.
E. Cadherins
C
In which state of the myosin cycle on actin is ATP hydrolyzed by myosin, leaving ADP and phosphate
bound to myosin?
A. Attached
B. Released
C. Cocked
D. Force generating
E. In all of the above (A, B, C or D); different ones for different molecules
C
During muscle relaxation (after contraction), the myosin filament gets progressively farther away from
A. The positive end of the actin filament.
B. The negative end of the actin filament.
C. The Z discs.
D. A and C are correct.
E. B and C are correct
D
In muscle cells, an action potential triggers influx of Ca++ to the cytosol mostly from _________to
trigger muscle contraction
A. The sarcoplasmic reticulum
B. T tubules
C. The extracellular fluid
D. The Golgi apparatus
E. There is no action potential – only influx of Ca+
A
