Question 1

Which of the following statements best describes the structural differences among the three main types of cytoskeletal filaments in eukaryotic cells?

Accepted Answer

Microfilaments are composed of actin subunits and are about 7 nm in diameter, intermediate filaments are composed of fibrous proteins and are about 10 nm in diameter, and microtubules are composed of tubulin subunits and are about 25 nm in diameter.

Question 2

A patient is treated with colchicine, a drug that binds tubulin monomers and inhibits their assembly. Which cellular process would be most directly affected?

Accepted Answer

Formation of the mitotic spindle during cell division

Question 3

Which of the following best explains the dynamic instability of microtubules?

Accepted Answer

Microtubules alternate between phases of growth and shrinkage due to the addition and loss of GTP-tubulin subunits, with the presence of a GTP cap stabilizing the growing end.

Question 4

Which protein is responsible for forming tight bundles of microtubules in axons and is implicated in neurodegenerative diseases when mutated?

Accepted Answer

Tau

Question 5

A scientist observes that a certain drug prevents the addition of new actin monomers to the plus ends of microfilaments. Which drug is most likely being used?

Accepted Answer

Cytochalasin D

Question 6

Which of the following intermediate filament proteins is most likely to be found in the nuclear lamina?

Accepted Answer

Lamin A

Question 7

A mutation in the TACC3 protein disrupts its phosphorylation by Aurora-A kinase. What is the most likely cellular consequence?

Accepted Answer

Impaired stabilization of kinetochore microtubules during mitosis

Question 8

Which of the following best describes the role of +TIP proteins such as CLIP-170 in microtubule dynamics?

Accepted Answer

+TIP proteins stabilize the growing plus ends of microtubules, reducing the likelihood of catastrophic depolymerization.

Question 9

Which of the following equations best represents the treadmilling phenomenon observed in actin microfilaments?

Accepted Answer

$$ k_{on}^{+} [ATP-actin] = k_{off}^{-} [ADP-actin] $$

Question 10

Which of the following best explains why intermediate filaments are considered the most stable cytoskeletal component?

Accepted Answer

They are not polarized and do not undergo rapid assembly and disassembly like microtubules and microfilaments.

Question 11

A cell is exposed to phalloidin, a toxin from the death cap fungus. What is the most likely effect on the cell's cytoskeleton?

Accepted Answer

Microfilaments will be stabilized and resistant to depolymerization.

Question 12

Which of the following linker proteins is responsible for connecting intermediate filaments to both microfilaments and microtubules?

Accepted Answer

Plectin

Question 13

Which of the following best describes the effect of a high concentration of GTP-tubulin on microtubule dynamics?

Accepted Answer

It promotes microtubule growth by maintaining a GTP cap at the plus end.

Question 14

Which class of intermediate filament proteins is most likely to be found in muscle cells and is important for contractile machinery?

Accepted Answer

Desmin (Class III)

Question 15

Which of the following best explains the role of katanin in microtubule dynamics?

Accepted Answer

Katanin severs microtubules, promoting their rapid disassembly.

Question 16

A researcher is studying a cell line that lacks functional MAP2. Which of the following is the most likely consequence?

Accepted Answer

Microtubules in dendrites will fail to form loose bundles.

Question 17

Which of the following best describes the function of the 'mesh' organelle discovered in mitotic spindles?

Accepted Answer

It stabilizes kinetochore microtubules by linking pairs of microtubules together via clathrin complexes.

Question 18

Which of the following best explains why intermediate filament typing can be used to distinguish different animal cell types?

Accepted Answer

Intermediate filament proteins are tissue-specific and differ in amino acid composition among cell types.

Question 19

Which of the following best describes the role of actin-binding proteins in the regulation of microfilament dynamics?

Accepted Answer

They control nucleation, elongation, severing, and organization of actin filaments.

Cytoskeletal Structure and Function: Microtubules, Microfilaments, and Intermediate Filaments

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