Q: Microtubules are composed of protofilaments made from which basic subunit?

A heterodimer of $$ ext{α}-$$tubulin and $$eta-$$tubulin.

Question 1

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

Accepted Answer

It is a network of interconnected filaments and tubules that is dynamic and supports cell shape, movement, and mechanical strength.

Question 2

Microtubules are composed of protofilaments made from which basic subunit?

Accepted Answer

A heterodimer of $$	ext{α}-$$tubulin and $$eta-$$tubulin.

Question 3

Which of the following best explains the concept of 'treadmilling' in microtubules?

Accepted Answer

Subunits are added to the plus end and removed from the minus end, causing the microtubule to move through the cytoplasm.

Question 4

The critical concentration ($$C_c) $$for microtubule assembly is defined as:

Accepted Answer

The concentration of tubulin dimers at which the rate of microtubule assembly equals the rate of disassembly.

Question 5

Which event triggers a microtubule 'catastrophe'?

Accepted Answer

The loss of the GTP-tubulin cap at the plus end, leading to rapid depolymerization.

Question 6

Which motor protein is responsible for moving cargo toward the minus ends of microtubules?

Accepted Answer

Cytoplasmic dynein

Question 7

A scientist treats cells with a drug that sequesters actin monomers, preventing their polymerization. What is the most likely effect on the cell?

Accepted Answer

Microfilament formation will be inhibited, affecting cell migration and shape.

Question 8

Which of the following best describes the structure of the axoneme in cilia and flagella?

Accepted Answer

A '9 + 2' arrangement: nine outer doublet microtubules and two central singlet microtubules.

Question 9

Which protein is responsible for crosslinking adjacent microtubule doublets in the axoneme, allowing for bending during ciliary movement?

Accepted Answer

Nexin

Question 10

Which of the following statements about intermediate filaments (IFs) is correct?

Accepted Answer

IFs are composed of fibrous proteins that form tension-bearing networks, providing mechanical strength.

Question 11

Which actin-binding protein promotes the growth of microfilaments in a particular direction by preventing monomer binding to the minus end?

Accepted Answer

Profilin

Question 12

During muscle contraction, which protein complex acts as a calcium-sensitive switch to activate contraction in striated muscle?

Accepted Answer

Troponin

Question 13

A mutation in the gene encoding katanin would most likely affect which cellular process?

Accepted Answer

Microtubule severing and turnover

Question 14

Which of the following best describes the polarity of microfilaments?

Accepted Answer

The plus (barbed) end grows faster than the minus (pointed) end due to ATP-actin addition.

Question 15

Which motor protein moves toward the plus end of actin filaments and is involved in vesicle transport?

Accepted Answer

Myosin V

Question 16

A cell is observed to have defective lamellipodia formation and impaired crawling movement. Which cytoskeletal element and associated protein are most likely affected?

Accepted Answer

Microfilaments and Arp2/3 complex

Question 17

Which equation correctly represents the relationship for microtubule growth in terms of tubulin concentration ($$[T]) $$and critical concentration ($$C_c$$)?

Accepted Answer

$$[T] \u003e C_c$$

Question 18

Which of the following is NOT a function of actin microfilaments?

Accepted Answer

Chromosome separation during mitosis

Question 19

Which process is directly powered by the hydrolysis of ATP in myosin motor proteins?

Accepted Answer

Actin-based muscle contraction

Question 20

A patient presents with a genetic disorder affecting the protein spectrin. Which cellular structure is most likely compromised?

Accepted Answer

The actin cortex beneath the plasma membrane, affecting cell shape and mechanical stability.

Cytoskeletal Systems: Structure and Function in Eukaryotic Cells

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