Question 1

Which of the following statements best describes the structural organization of a microtubule?

Accepted Answer

Microtubules are hollow cylinders made up of 13 protofilaments, each consisting of αβ-tubulin heterodimers.

Question 2

A researcher adds a drug to a cell culture that binds tightly to microtubules and prevents their disassembly. What is the most likely effect on mitosis?

Accepted Answer

The mitotic spindle will assemble but chromosomes will not separate properly.

Question 3

Which of the following best explains why microtubule assembly occurs more rapidly at the plus end than at the minus end?

Accepted Answer

The plus end has a higher affinity for GTP-bound tubulin dimers.

Question 4

If the concentration of tubulin dimers is above the critical concentration for the plus end but below the critical concentration for the minus end, what will happen to a microtubule in vitro?

Accepted Answer

The microtubule will grow at the plus end and shrink at the minus end, resulting in treadmilling.

Question 5

Which protein complex is responsible for nucleating the assembly of new microtubules at the centrosome?

Accepted Answer

γ-TuRC (gamma-tubulin ring complex)

Question 6

A patient is treated with colchicine, a drug that binds β-tubulin and inhibits microtubule assembly. Which cellular process is most directly affected?

Accepted Answer

Mitotic spindle formation during cell division

Question 7

Which of the following best describes the role of microtubule-associated protein Tau in neurons?

Accepted Answer

Tau stabilizes microtubules and promotes the formation of tight bundles in axons.

Question 8

Which of the following is a key difference between microfilaments and microtubules?

Accepted Answer

Microfilaments are composed of actin, while microtubules are composed of tubulin heterodimers.

Question 9

Which of the following best describes the polarity of actin filaments (microfilaments)?

Accepted Answer

Actin filaments have distinct plus and minus ends, with faster growth at the plus end.

Question 10

A cell is observed to have prominent stress fibers and a well-developed cell cortex. Which cytoskeletal component is primarily responsible for these structures?

Accepted Answer

Microfilaments (actin filaments)

Question 11

Which Rho family GTPase is primarily responsible for promoting the formation of lamellipodia in migrating cells?

Accepted Answer

Rac

Question 12

Which of the following statements about intermediate filaments is correct?

Accepted Answer

Intermediate filaments are the most stable and least soluble cytoskeletal components.

Question 13

A pathologist is trying to determine the tissue of origin for a metastatic tumor. Which property of intermediate filaments is most useful for this purpose?

Accepted Answer

Intermediate filament proteins are tissue-specific and can be used as markers for cell type.

Question 14

Which of the following best describes the function of spectraplakins such as plectin?

Accepted Answer

They link microtubules, microfilaments, and intermediate filaments to integrate the cytoskeleton.

Question 15

Which of the following best explains why microvilli in intestinal epithelial cells are able to maintain their structure and increase surface area?

Accepted Answer

Microvilli contain tightly bundled actin filaments crosslinked by fimbrin and villin.

Question 16

Which of the following scenarios best illustrates the concept of 'treadmilling' in actin filaments?

Accepted Answer

Actin monomers are added to the plus end and removed from the minus end at equal rates, resulting in a filament of constant length.

Question 17

Which of the following best describes the role of γ-tubulin in microtubule organization?

Accepted Answer

γ-tubulin nucleates microtubule assembly at the centrosome by forming a ring complex.

Question 18

A cell is exposed to a growth factor that activates Cdc42. Which cytoskeletal structure is most likely to be enhanced?

Accepted Answer

Filopodia

Question 19

Which of the following best explains the mechanical integration of the cytoskeleton?

Accepted Answer

Microtubules resist compression, microfilaments generate tension, and intermediate filaments withstand tensile forces.

Cytoskeletal Systems: Structure, Function, and Regulation

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