Question 1

Which of the following statements best describes the role of GTP in microtubule dynamics?

Accepted Answer

GTP binds to β-tubulin, and its hydrolysis to GDP destabilizes the microtubule, promoting dynamic instability.

Question 2

A researcher is testing a new drug that binds to the plus end of actin filaments and prevents both addition and loss of actin subunits. Which protein does this drug most closely mimic?

Accepted Answer

CapZ

Question 3

Which cytoskeletal element is most directly responsible for resisting tensile (stretching) forces in animal tissues?

Accepted Answer

Intermediate filaments

Question 4

A cancer cell line is treated with paclitaxel (Taxol). What is the most likely effect on the cell cycle?

Accepted Answer

Cells will arrest in mitosis due to stabilized microtubules and depletion of free tubulin.

Question 5

Which of the following best explains why microtubules exhibit 'dynamic instability'?

Accepted Answer

Microtubules alternate between phases of growth and shrinkage due to the presence or absence of a GTP cap.

Question 6

A mutation in the gene encoding Tau protein is most likely to affect which cellular structure or function?

Accepted Answer

Formation of tight microtubule bundles in axons

Question 7

Which of the following best describes the process of treadmilling in microtubules?

Accepted Answer

Simultaneous addition of tubulin subunits at the plus end and removal at the minus end, resulting in a net movement of subunits through the microtubule.

Question 8

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

Accepted Answer

Microtubules exhibit dynamic instability, while intermediate filaments are more stable and do not.

Question 9

A patient with a genetic defect in keratin is most likely to experience which of the following symptoms?

Accepted Answer

Fragile skin and blistering due to weakened intermediate filaments

Question 10

Which of the following best describes the role of the centrosome in animal cells?

Accepted Answer

It serves as the primary microtubule-organizing center (MTOC), anchoring the minus ends of microtubules.

Question 11

Which of the following equations correctly represents the critical concentration ($$C_c) $$for microtubule assembly?

Accepted Answer

$$C_c = \frac{k_{off}}{k_{on}}$$

Question 12

Which of the following best explains why antimitotic drugs such as vinblastine are effective in cancer therapy?

Accepted Answer

They inhibit microtubule assembly, preventing spindle formation and arresting rapidly dividing cells in mitosis.

Question 13

Which of the following proteins is responsible for crosslinking actin filaments into a gel-like network in the cell cortex?

Accepted Answer

Filamin

Question 14

A scientist isolates a cytoskeletal filament that is 10 nm in diameter, highly stable, and composed of a single type of protein subunit. Which filament has most likely been isolated?

Accepted Answer

Intermediate filament

Question 15

Which of the following best describes the polarity of actin filaments?

Accepted Answer

The plus end grows faster than the minus end, and ATP-actin is found at the growing end.

Question 16

Which of the following scenarios would most likely result in microtubule catastrophe?

Accepted Answer

A decrease in GTP-tubulin concentration below the rate of GTP hydrolysis at the plus end.

Question 17

Which of the following is a function of nuclear lamins?

Accepted Answer

They support the inner nuclear membrane and organize nuclear structure.

Question 18

Which of the following best describes the role of myosin I in cells?

Accepted Answer

It is a motor protein that moves along actin filaments to transport vesicles and position organelles.

Question 19

Which of the following best explains why intermediate filaments are less susceptible to chemical attack than microtubules or microfilaments?

Accepted Answer

They are composed of highly stable fibrous proteins and do not exhibit dynamic instability.

Cytoskeletal Systems: Structure, Function, and Dynamics

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