Cytoskeleton Flashcards: Fibers, Motors & Functions

Question 1

What are the three major cytoskeletal filament families in animal cells?

Accepted Answer

Actin filaments (microfilaments), microtubules, and intermediate filaments.

Question 2

Which protein builds microfilaments?

Accepted Answer

Actin.

Question 3

Which two tubulin subunits pair to build microtubules?

Accepted Answer

Alpha-tubulin and beta-tubulin. Each building unit is an alpha–beta tubulin dimer.

Question 4

Do all intermediate filaments use the same building protein?

Accepted Answer

No. Different cells use different intermediate-filament proteins, such as keratins, vimentin, and nuclear lamins.

Question 5

What does filament polarity mean in the cytoskeleton?

Accepted Answer

The two ends have different molecular structures. Plus and minus label distinct ends, not electrical charges.

Question 6

What is the basic shape of an actin filament?

Accepted Answer

Two intertwined strands of actin subunits. It is a thin filament, not a hollow tube.

Question 7

Which major cytoskeletal filament forms a hollow tube?

Accepted Answer

A microtubule.

Question 8

Which major cytoskeletal filament has a rope-like assembly of fibrous proteins?

Accepted Answer

An intermediate filament.

Question 9

Which cytoskeletal filament is the track for myosin motors?

Accepted Answer

An actin filament.

Question 10

Which major cytoskeletal filament family lacks distinct plus and minus ends?

Accepted Answer

Intermediate filaments. Actin filaments and microtubules are polar.

Question 11

What directly powers the stepping of myosin, kinesin, and dynein motors?

Accepted Answer

ATP hydrolysis.

Question 12

Which two motor-protein families move along microtubules?

Accepted Answer

Kinesins and dyneins.

Question 13

Which filament network is especially prominent in the cortex just beneath an animal cell’s plasma membrane?

Accepted Answer

Actin filaments. The cortex helps control cell shape and surface mechanics.

Question 14

Keratin networks belong to which cytoskeletal filament family?

Accepted Answer

Intermediate filaments.

Question 15

What is microtubule dynamic instability?

Accepted Answer

Switching between growth and shrinkage. A microtubule can change length as tubulin subunits are added or lost.

Question 16

A cargo moves by kinesin along a microtubule. Which component is the motor?

Accepted Answer

Kinesin. The microtubule is the track.

Question 17

Which filaments form the supporting bundles inside microvilli?

Accepted Answer

Actin filaments.

Question 18

Which proteins form the nuclear lamina beneath the inner nuclear membrane?

Accepted Answer

Lamins, members of the intermediate-filament protein family.

Question 19

Which cytoskeletal filaments form the mitotic spindle?

Accepted Answer

Microtubules. Spindle microtubules help organize and separate chromosomes.

Question 20

Cytoplasmic dynein carries cargo toward which end of a microtubule?

Accepted Answer

The minus end.

Question 21

Which filament and motor form the main contractile machinery of the animal-cell cleavage ring?

Accepted Answer

Actin filaments and myosin II.

Question 22

How can actin assembly help a crawling cell extend its leading edge?

Accepted Answer

Growing actin filaments can push the plasma membrane outward.

Question 23

Which filaments form the axoneme, the internal framework of eukaryotic cilia and flagella?

Accepted Answer

Microtubules.

Question 24

Conventional kinesin-1 carries cargo toward which end of a microtubule?

Accepted Answer

The plus end.

Question 25

What mechanical role do intermediate-filament networks provide when a cell is stretched?

Accepted Answer

They help distribute tensile stress and resist damage from stretching.

Question 26

In an animal-cell contractile ring, is myosin II a motor or an actin building subunit?

Accepted Answer

A motor. Actin supplies the filament subunits.

Question 27

What does the typical 9 + 2 pattern of an airway motile cilium describe?

Accepted Answer

Nine outer microtubule doublets around two central single microtubules.

Question 28

Does the name kinesin alone guarantee plus-end-directed movement?

Accepted Answer

No. Kinesin families differ; some move toward minus ends. Specify the kinesin type before assigning a direction.

Question 29

How do the core filaments of microvilli differ from those of eukaryotic cilia?

Accepted Answer

Microvilli have actin bundles; cilia have a microtubule-based axoneme.

Question 30

The nuclear lamina is built from which major filament family?

Accepted Answer

Intermediate filaments, specifically lamins.

Question 31

In animal-cell division, which structure constricts the cell surface: the spindle or the contractile ring?

Accepted Answer

The contractile ring. Its actin–myosin machinery narrows the cleavage furrow.

Question 32

What is a common role of a non-motile primary cilium?

Accepted Answer

Sensing and coordinating signals. It acts as a specialized signaling compartment.

Question 33

Which motor family drives sliding between neighboring microtubule doublets in a motile cilium?

Accepted Answer

Axonemal dyneins. Structural constraints convert that sliding into bending.

Question 34

Does vesicle transport by itself identify a microtubule track?

Accepted Answer

No. Vesicles can use microtubules or actin-based transport. The motor identity or filament composition supplies a better clue.

Question 35

A prompt asks for the filament family containing keratin. Is keratin alone the requested answer?

Accepted Answer

No. Answer intermediate filaments. Keratin names a building protein, not the filament family.

Question 36

What microtubule pattern is commonly used to describe a primary cilium?

Accepted Answer

The 9 + 0 pattern: nine outer doublets without a central pair. It is a typical description, not a universal rule for every cross-section.

Question 37

A filament is assembled from alpha–beta tubulin dimers. Which filament family is it?

Accepted Answer

Microtubules.

Question 38

What does the centrosome do for microtubules in many animal cells?

Accepted Answer

It acts as a microtubule-organizing center, helping nucleate and organize the microtubule array.

Question 39

A vesicle is moved by myosin. Which filament supplies its track?

Accepted Answer

Actin. Myosin-based cargo transport uses actin filaments.

Question 40

Why can’t a 9 + 0 axoneme alone establish that a cilium is non-motile?

Accepted Answer

Motile embryonic nodal cilia are a counterexample. Arrangement alone does not establish motility.

Question 41

What extra clue would help identify a fiber described only as supporting cell shape?

Accepted Answer

Its protein composition or a specific structure it forms. All three major filament systems contribute to cell mechanics.

Question 42

Why is the claim that all intermediate filaments lie in the cytoplasm incorrect?

Accepted Answer

Lamins form the nuclear lamina inside the nucleus.

Question 43

In a 9 + 2 axoneme, does the 9 count nine individual microtubules?

Accepted Answer

No. It counts nine outer doublets. The central 2 counts two single microtubules.

Question 44

An ATP-powered motor uses either actin or microtubules. What missing information would identify its track?

Accepted Answer

The motor family. Myosins use actin; kinesins and dyneins use microtubules. ATP use alone does not distinguish them.

Question 45

What missing detail would distinguish fibers described only as helping animal-cell division?

Accepted Answer

The division structure or step. Spindle fibers are microtubules; the contractile ring contains actin.

Question 46

A student says microvilli are miniature cilia because both project from the cell. What core-filament correction is needed?

Accepted Answer

Microvilli are supported by actin bundles; cilia have a microtubule-based core. Surface shape alone does not make them the same structure.

Question 47

In microtubule-based transport, how does the filament’s role differ from the motor’s?

Accepted Answer

The microtubule supplies a track; kinesin or dynein supplies motor activity.

Question 48

What extra detail is needed to identify a cytoskeletal system described only as enabling cell movement?

Accepted Answer

The type of movement. Actin supports crawling; microtubules and dyneins support ciliary or flagellar motion.

Question 49

Is it accurate to say that microtubules have no role in animal-cell cytokinesis because the ring uses actin?

Accepted Answer

No. Microtubules also help coordinate cytokinesis, including positioning and organizing the division machinery.

Question 50

Is the cytoskeleton a permanent, unchanging scaffold?

Accepted Answer

No. Its filaments and networks can assemble, disassemble, and reorganize as the cell’s needs change.

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Cytoskeleton Flashcards: Fibers, Motors & Functions