Q: Which of the following equations best represents the treadmilling phenomenon in actin filaments?

$$ \text{Rate of addition at plus end} = \text{Rate of loss at minus end} $$

Question 1

Which of the following statements best describes the dynamic instability of microtubules in eukaryotic cells?

Accepted Answer

Microtubules undergo rapid, stochastic transitions between growth and shrinkage at their plus ends, regulated by the presence or absence of a GTP cap.

Question 2

A researcher treats dividing cancer cells with Taxol (Paclitaxel). What is the most likely cellular effect of this drug?

Accepted Answer

It stabilizes microtubules, preventing their depolymerization and causing mitotic arrest due to failure of spindle dynamics.

Question 3

Which protein is responsible for nucleating branched actin filament networks in lamellipodia?

Accepted Answer

Arp2/3 complex

Question 4

A mutation in the Tau protein leads to its hyperphosphorylation. What cellular structure is most directly affected, and what disease is this associated with?

Accepted Answer

Microtubule bundles in neurons; Alzheimer's disease

Question 5

Which of the following best explains the polarity of actin microfilaments?

Accepted Answer

Actin filaments have distinct plus (barbed) and minus (pointed) ends due to the uniform orientation of actin monomers during polymerization.

Question 6

Which cytoskeletal element is primarily responsible for the formation of the mitotic spindle during cell division?

Accepted Answer

Microtubules

Question 7

Listeria monocytogenes uses the host cell's actin cytoskeleton to move within and between cells. Which host protein does Listeria mimic to nucleate actin polymerization?

Accepted Answer

ActA, which mimics the function of WASP family proteins to activate the Arp2/3 complex

Question 8

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

Accepted Answer

$$ 	ext{Rate of addition at plus end} = 	ext{Rate of loss at minus end} $$

Question 9

Which microtubule-associated protein is known to stabilize the plus end of microtubules and decrease the likelihood of catastrophic disassembly?

Accepted Answer

EB1 (+TIP protein)

Question 10

A cell is exposed to a Rho GTPase activating protein (GAP). What is the expected effect on the cytoskeleton?

Accepted Answer

Decreased formation of stress fibers due to inactivation of Rho by GTP hydrolysis

Question 11

Which of the following best describes the structure of a microtubule found in cilia and flagella?

Accepted Answer

A doublet microtubule consisting of one complete A tubule (13 protofilaments) and one incomplete B tubule (10-11 protofilaments)

Question 12

Which protein severs microtubules and is important for regulating their length and organization?

Accepted Answer

Katanin

Question 13

Which of the following drugs binds to tubulin heterodimers and prevents further addition of subunits, promoting microtubule disassembly?

Accepted Answer

Colchicine

Question 14

Which actin-binding protein promotes the assembly of actin filaments at the plus end by competing with thymosin β4 for G-actin binding?

Accepted Answer

Profilin

Question 15

What is the primary function of the γ-tubulin ring complex (γ-TuRC) in the centrosome?

Accepted Answer

Nucleation of new microtubules at the minus end

Question 16

Which of the following best describes the role of formin proteins in actin filament dynamics?

Accepted Answer

Formins nucleate and promote the elongation of long, unbranched actin filaments independently of the Arp2/3 complex.

Question 17

Which equation best represents the energy requirement for microtubule assembly?

Accepted Answer

$$ 	ext{Tubulin dimer} + GTP + Mg$$^{2+}$$ ightarrow 	ext{Microtubule polymer} $$

Question 18

Which cytoskeletal element is most directly involved in the maintenance of animal cell shape and intracellular transport/trafficking?

Accepted Answer

Microfilaments (actin filaments)

Question 19

Which protein binds to the plus end of actin filaments to prevent the addition of new subunits?

Accepted Answer

CapZ

Cytoskeletal Systems: Microfilaments and Microtubules in Eukaryotic Cells

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