Question 1

Which of the following statements best describes the cytoskeleton in eukaryotic cells?

Accepted Answer

It is a dynamic network of interconnected filaments and tubules that is not membrane-bound and plays roles in cell movement, shape, and division.

Question 2

Which of the following is NOT a major structural element of the cytoskeleton?

Accepted Answer

Lysosomes

Question 3

Microtubules are composed of which protein subunits?

Accepted Answer

Tubulin heterodimers, consisting of alpha- and beta-tubulin

Question 4

Which of the following best explains the concept of 'dynamic instability' in microtubules?

Accepted Answer

Microtubules alternate between phases of growth and shrinkage, depending on the presence of a GTP cap at the plus end.

Question 5

A researcher adds a drug to cultured cells that binds tightly to microtubules and stabilizes them, causing a depletion of free tubulin subunits. Which drug is most likely being used?

Accepted Answer

Taxol

Question 6

Which of the following best describes the difference between cytoplasmic and axonemal microtubules?

Accepted Answer

Cytoplasmic microtubules are dynamic and involved in cell shape and division, while axonemal microtubules are stable and found in structures like cilia and flagella.

Question 7

Which of the following statements about microtubule assembly is correct?

Accepted Answer

Microtubules grow when the tubulin concentration exceeds the critical concentration.

Question 8

A cell is treated with colchicine. What is the most likely effect on microtubules?

Accepted Answer

Microtubule assembly is inhibited, leading to increased disassembly.

Question 9

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

Accepted Answer

Addition of subunits at the plus end and removal from the minus end, resulting in a net movement of subunits through the microtubule.

Question 10

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 11

During microtubule assembly, what is the role of GTP bound to beta-tubulin?

Accepted Answer

It is hydrolyzed after the dimer is incorporated into the microtubule, promoting instability and disassembly.

Question 12

A sudden loss of the GTP cap at the plus end of a microtubule leads to which event?

Accepted Answer

Microtubule catastrophe

Question 13

Which of the following best describes the structure of a centriole?

Accepted Answer

Nine pairs of triplet microtubules arranged in a cylinder

Question 14

Which of the following is a function of cytoplasmic microtubules?

Accepted Answer

Maintaining axons and forming mitotic and meiotic spindles

Question 15

Which of the following best explains why taxol is effective as an anti-cancer drug?

Accepted Answer

It stabilizes microtubules, preventing their disassembly and thus inhibiting cell division.

Question 16

Which of the following statements about microtubule polarity is correct?

Accepted Answer

The plus end grows faster than the minus end due to structural differences in tubulin dimer orientation.

Question 17

A scientist observes that microtubules in a cell are rapidly growing and shrinking at their plus ends, but the minus ends remain relatively stable. Which model best explains this behavior?

Accepted Answer

Dynamic instability model

Question 18

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

Accepted Answer

It serves as the main microtubule-organizing center (MTOC) near the nucleus.

Question 19

Which of the following drugs is most likely to cause rapid disassembly of microtubules by binding to tubulin dimers and inhibiting their assembly?

Accepted Answer

Colchicine

Question 20

If the concentration of free tubulin is above the critical concentration for the plus end but below that for the minus end, what will happen to the microtubule?

Accepted Answer

It will treadmill, adding subunits at the plus end and losing them at the minus end.

Cytoskeletal Systems: Structure and Dynamics of Microtubules

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