Cytoskeleton II - Microtubules

What are microtubules made of?
A. Actin monomers
B. Tubulin heterodimers
C. Intermediate filaments
D. Lamin proteins

B. Tubulin heterodimers

Which end of a microtubule has β-tubulin exposed?
A. Minus end
B. Plus end
C. Lateral end
D. None of the above

B. Plus end

How many protofilaments typically form one microtubule?
A. 9
B. 10
C. 13
D. 15

C. 13

What promotes microtubule disassembly by destabilizing the plus end?
A. GTP-bound β-tubulin
B. GDP-bound β-tubulin
C. α-tubulin
D. γ-tubulin

B. GDP-bound β-tubulin

What is ‘catastrophe’ in the context of microtubule dynamics?
A. Tubulin dimer formation
B. Rapid switch from growth to shrinkage
C. Microtubule nucleation
D. Formation of the centrosome

B. Rapid switch from growth to shrinkage

What causes microtubule treadmilling?
A. Equal addition and loss at both ends
B. Higher critical concentration at the plus end
C. GTP hydrolysis faster than tubulin addition
D. Differential critical concentrations at plus and minus ends

D. Differential critical concentrations at plus and minus ends

Which protein complex is responsible for microtubule nucleation?
A. MAP2
B. γ-TuRC
C. Arp2/3
D. XMAP215

B. γ-TuRC

Where in animal cells are microtubules typically nucleated?
A. Cell membrane
B. Mitochondria
C. Centrosome
D. Nucleus

C. Centrosome

What is the role of augmin?
A. Caps microtubule plus ends
B. Sever microtubules
C. Nucleate branching microtubules
D. Promote catastrophe

C. Nucleate branching microtubules

Which MAP has a longer projection domain and promotes wider spacing in bundles?
A. Tau
B. MAP2
C. Stathmin
D. Katanin

B. MAP2

Which MAP promotes rapid microtubule polymerization?
A. Kinesin-13
B. Dynein
C. XMAP215
D. Tau

C. XMAP215

What does stathmin do?
A. Sever microtubules
B. Bind tubulin dimers to prevent polymerization
C. Promote rescue
D. Stabilize GTP cap

B. Bind tubulin dimers to prevent polymerization

Which motor protein moves cargo toward the microtubule minus end?
A. Kinesin-1
B. Dynein
C. Kinesin-5
D. MAP2

B. Dynein

Which kinesin promotes microtubule depolymerization instead of movement?
A. Kinesin-1
B. Kinesin-5
C. Kinesin-13
D. Kinesin-14

C. Kinesin-13

Which of the following statements is TRUE about kinesin-1?
A. It moves toward the minus end.
B. It uses ATP to sever microtubules.
C. It performs a “hand-over-hand” stepping motion.
D. It promotes microtubule shrinkage.

C. It performs a “hand-over-hand” stepping motion.

What happens to GTP when tubulin dimers are added to a microtubule?
A. It stays intact indefinitely
B. It is exchanged for ATP
C. It is rapidly hydrolyzed to GDP
D. It remains bound to β-tubulin permanently

C. It is rapidly hydrolyzed to GDP

Which form of tubulin favors microtubule polymerization?
A. GDP-bound
B. ADP-bound
C. T-form (GTP-bound)
D. None of the above

C. T-form (GTP-bound)

Which of the following best describes the “seam” in a microtubule?
A. The site of GTP hydrolysis
B. The site where protofilaments stagger slightly
C. The centriole duplication point
D. The attachment site for organelles

B. The site where protofilaments stagger slightly

What role does the pericentriolar material in the centrosome serve?
A. It hydrolyzes GTP
B. It houses γ-TuRC for microtubule nucleation
C. It forms protofilaments
D. It stores free tubulin dimers

B. It houses γ-TuRC for microtubule nucleation

Which of the following cells lack centrosomes?
A. Animal epithelial cells
B. Yeast
C. Higher plant cells
D. Fibroblasts

C. Higher plant cells

Which structure in budding yeast acts as the MTOC?
A. Centrosome
B. Spindle pole body
C. Cell cortex
D. Nucleolus

B. Spindle pole body

How are microtubules arranged in neuronal axons?
A. Randomly
B. With plus ends toward the cell body
C. With minus ends toward the axon terminals
D. With plus ends toward the axon terminals

D. With plus ends toward the axon terminals

Which protein binds along the sides of existing microtubules to promote branching nucleation?
A. Tau
B. Augmin
C. Stathmin
D. Kinesin-13

B. Augmin

What is the effect of katanin on microtubules?
A. Promotes nucleation at the centrosome
B. Stabilizes plus ends
C. Severing microtubules using ATP
D. Inhibits polymerization by binding free tubulin

C. Severing microtubules using ATP

Which protein is most likely to increase microtubule dynamic instability by sequestering free tubulin dimers?
A. MAP2
B. Stathmin
C. Dynein
D. γ-Tubulin

B. Stathmin

What paradox is observed in cells lacking microtubule-severing proteins?
A. Excess microtubule growth
B. No effect on dynamics
C. Fewer, not more, microtubules
D. Inability to polymerize GTP

C. Fewer, not more, microtubules

Which kinesin family member travels toward the minus end of microtubules?
A. Kinesin-1
B. Kinesin-5
C. Kinesin-14
D. Kinesin-13

C. Kinesin-14

Which statement about cytoplasmic dynein is TRUE?
A. It is a monomeric motor protein
B. It has smaller heads than kinesin
C. It transports cargo toward the plus end
D. It requires accessory proteins to bind organelles

D. It requires accessory proteins to bind organelles

What complex connects dynein to cargo such as vesicles?
A. γ-TuRC
B. Dynactin
C. Augmin
D. MAP2

B. Dynactin

In angelfish melanophores, what causes melanosomes to disperse?
A. Dynein activation
B. Katanin-mediated severing
C. Kinesin-2 activity
D. Centrosome disruption

C. Kinesin-2 activity