Question 1

Which of the following statements best describes the role of the centrosome in a eukaryotic cell?

Accepted Answer

It serves as the microtubule organizing center (MTOC), nucleating microtubules and stabilizing their minus ends.

Question 2

Taxol is a chemotherapy drug used to treat breast cancer. What is its primary mechanism of action at the cellular level?

Accepted Answer

It binds to and stabilizes microtubules, preventing their dynamic growth and shrinkage, thereby blocking cell division.

Question 3

Which of the following correctly describes the difference between kinesin and dynein motor proteins?

Accepted Answer

Kinesin moves cargo towards the plus end of microtubules (cell periphery), while dynein moves cargo towards the minus end (cell center).

Question 4

Microtubules are composed of which protein subunits, and what is their nucleotide binding property?

Accepted Answer

Alpha- and beta-tubulin dimers, which bind GTP that is hydrolyzed to GDP after incorporation into the microtubule.

Question 5

A scientist removes ATP from a cell extract containing microtubules and organelles. What is the most likely observation regarding organelle movement?

Accepted Answer

Organelle movement along microtubules will cease because motor proteins require ATP hydrolysis for movement.

Question 6

Which equation correctly represents the hydrolysis of ATP by motor proteins during cargo transport?

Accepted Answer

$$\mathrm{ATP} \rightarrow \mathrm{ADP} + \mathrm{P_i}$$

Question 7

Which property makes kinesin a 'processive' motor protein?

Accepted Answer

Kinesin can take many steps along a microtubule without dissociating because one head is always firmly bound.

Question 8

Which of the following best explains why actin filaments are considered 'dynamic' structures in cells?

Accepted Answer

Actin filaments grow at the plus end and dissociate at the minus end, with ATP hydrolysis occurring after incorporation.

Question 9

During muscle contraction, which mechanism is responsible for the sliding of actin filaments past myosin filaments?

Accepted Answer

The power stroke generated by myosin head conformational change after phosphate release.

Question 10

Which of the following is NOT a function of the cytoskeleton in eukaryotic cells?

Accepted Answer

Catalyzing the hydrolysis of glucose during glycolysis.

Question 11

A mutation causes the neck linker region of kinesin to lose its ability to undergo conformational change. What is the most likely cellular consequence?

Accepted Answer

Kinesin will be unable to move cargo efficiently along microtubules, impairing organelle transport.

Question 12

Which of the following statements about myosin motors in muscle contraction is correct?

Accepted Answer

ATP binding causes the release of myosin from actin, and subsequent hydrolysis 'cocks' the myosin head for the next power stroke.

Question 13

Which of the following best describes the difference in nucleotide binding between actin and tubulin?

Accepted Answer

Actin binds ATP, which is hydrolyzed to ADP after incorporation; tubulin binds GTP, which is hydrolyzed to GDP after incorporation.

Question 14

Which of the following is a correct statement about intermediate filaments?

Accepted Answer

They provide mechanical strength to cells and tissues, such as keratin in skin.

Question 15

Which of the following scenarios would most likely result in impaired cell division?

Accepted Answer

Treatment with Taxol, which stabilizes microtubules and prevents spindle dynamics.

Question 16

Which of the following best explains why myosin motors in muscle are considered 'non-processive'?

Accepted Answer

Each myosin head works independently, and does not remain attached for multiple cycles.

Question 17

Which of the following is a correct sequence of events in the myosin-actin cycle during muscle contraction?

Accepted Answer

ATP binds to myosin, myosin releases actin, ATP is hydrolyzed, myosin binds actin, phosphate is released, power stroke occurs.

Question 18

Which of the following best describes the role of actin-binding proteins in cells?

Accepted Answer

They control the behavior of actin filaments, including nucleation, stabilization, and organization.

The Cytoskeleton and Molecular Motors: Structure and Function in Cells

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