Cytoskeleton

Question 1

What are the functions of the cystoskeleton?

A) Structual integrity
B) Cell motility
C) Contraction
D) Organization
E) All of the above

Answer 1

E

Question 2

Which are the thickest filaments?

A) Microtubules
B) Cytoskeleton
C) Actin filaments
D) intermediate filaments

Answer 2

A

Question 3

Pairs form stable polar dimers via coiled-coils , with head to
head and tail to tail
A) IF
B) Actin
C) Centerometers
D) MT

Answer 3

A)

Question 3

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

Answer 3

E

Question 4

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

Answer 4

C

Question 5

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

Answer 5

B

Question 6

What does the Lamin of IFs form?

Answer 6

Nuclear lamina

Question 6

IFs provide strength to withstand mechanical
stress (resistance to stretching; tensile
strength) via what?

A) IF
B) MT
C) Sheets
D) desmosome

Answer 6

D

Question 7

Why does the cell rupture between the nucleus of mice which leads to blitsering skin

Answer 7

Keratin mutant

Question 8

What is Pectin and why is important to IFS?

Answer 8

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

Question 9

What causes progeria (“premature aging”) ?

Answer 9

Phosphorylation results in
weakened binding between tetramers, due to disassembly of Lamins

Question 10

Four classes of IFs

Answer 10

Keratins, Vimentin, neurofilaments, nuclear Lamins

Question 11

Assembly
controlled by
phosphorylation?

Answer 11

Nuclear Lamins

Question 12

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.

Answer 12

C

Question 13

Microtubles

Answer 13

• 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

Question 14

What is the structure polarity of MTs?

Answer 14

Alpha (-), Beta (+), dimers stacks to form protofilaments

Question 15

How many protofilaments of MT form a hollow tube?

A)10
B)15
C)13
D) 12

Answer 15

C

Question 16

How many centrioles are in the centrioles in most animal cells ?

Answer 16

Two

Question 17

MTOC of yeast and budding yeast

A) 3
B)1
C) 4
D) 0

Answer 17

B

Question 18

HOW many MTOC of Plant cell and intestinal epithelial cell?

Answer 18

Many

Question 19

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.

Answer 19

B

Question 20

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

Answer 20

B

Question 21

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

Answer 21

A

Question 22

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

Answer 22

C)

Question 23

Dyneins move toward the

Answer 23

minus end

Question 24

Two types of MT motor proteins Kinesins move toward the

Answer 24

Plus end

Question 25

What cargoes move along MTs?

Answer 25

Membrane enclosed organales, vesicles, and indivudual proteins

Question 25

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

Answer 25

ATP hydrolysis

Question 26

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)

Answer 26

E

Question 27

Structure: MTs arranged in a ___ array A) 9+3 B)3+5 C)9+1 D) 9+2

Answer 27

D

Question 28

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

Answer 28

B

Question 29

How many doublets in outer ring of MTs A) 6 B) 9 C) 8 D) 2

Answer 29

B

Question 30

Outer ring and central pair are linked by ___and ______, and there are dynein motors that generate the movements

Answer 30

“spokes” and “rim”

Question 31

The AF is inherently unstable and can disassemble from the - end; ____ stabilizes, ____ produced by hydrolysis after assembly destabilizes

Answer 31

ATP, ADP

Question 31

Structural polarity of AFs

Answer 31

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

Question 32

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

Answer 32

C

Question 33

These drugs freeze cell movements because assembly and disassembly are both required. A) Phalloidin B) Cytochalasin C) Latrunculin D) all of the above

Answer 33

D

Question 34

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

Answer 34

A

Question 35

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

Answer 35

C

Question 36

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

Answer 36

B

Question 37

Thymosin profilin A) monomer squeezing protein B) Motor protein C) cross linking protein D severing protein

Answer 37

A

Question 38

Gelsolin does what

Answer 38

Breaks

Question 39

Lamellipodia are a sheetlike leading edge with a dense meshwork of _____ filaments - Plus ends close to ______

Answer 39

Actin, plasma membrane

Question 40

Filopdia are thin, stiff protrusions formed by _______ of filaments. Plus end close to _____

Answer 40

loose bundle, membrane

Question 41

What are the three main steps to crawling ?

Answer 41

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

Question 42

Myosin I (one head domain) in _______ types. Myosin II (two head domains in a dimer) in _______types also.

Answer 42

All cell, muscle and other cell

Question 43

What triggers formation of lamellipodia? A) Cdc42 B) Rho C) Rac

Answer 43

C

Question 44

What triggers polymerization to form filopodia? A) Cdc42 B) Rho C) Rac

Answer 44

A)

Question 45

Sarcomere is contractile unit. ___ ends of actin filaments are anchored at Z disc. -Actin and myosin filaments overlap

Answer 45

PLus ends

Question 46

No bound nucleotide or phosphate Myosin locked onto actin A) Released B) Attactched C) Cocked D) Rebinding and power stroke

Answer 46

B

Question 47

Myosin binds ATP Releases actin A) Released B) Attactched C) Cocked D) Rebinding and power stroke

Answer 47

A

Question 48

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

Answer 48

C

Question 49

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.

Answer 49

E

Question 50

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

Answer 50

C

Question 51

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

Answer 51

B

Question 52

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

Answer 52

B

Question 53

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.

Answer 53

D

Question 54

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).

Answer 54

E

Question 55

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

Answer 55

B

Question 56

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

Answer 56

B

Question 57

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.

Answer 57

E

Question 58

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

Answer 58

E

Question 59

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

Answer 59

C

Question 60

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

Answer 60

C

Question 61

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

Answer 61

D

Question 62

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+

Answer 62

A