29 Questions
What is the result of all the monomers within an actin filament being pointed in the same direction?
The filament becomes polar with 'barbed' and 'pointed' ends
Which molecule does an actin monomer bind before being incorporated into a filament?
ATP
What kind of enzyme is actin, as mentioned in the text?
ATPase
Which end of an actin filament incorporates monomers at a rate about 10 times faster than the other end?
Barbed end
What occurs much more rapidly in actin filament formation after the initial nucleation event?
Filament elongation
What defines actin as a major protein in every eukaryotic cell?
Its ATPase activity
What is the characteristic of kinesin that allows it to walk along a microtubule for considerable distances without falling off?
Its hand-over-hand movement mechanism
What is the primary function of kinesin-mediated organelle transport?
To drive the movement of cargo and organelles in an outward direction toward the cell's plasma membrane
How does the movement of cytoplasmic dynein along a microtubule compare to that of most kinesins?
Cytoplasmic dynein moves in the opposite direction to most kinesins, toward the minus end of the microtubule.
What is the structure of a cytoplasmic dynein molecule?
Two identical heavy chains, a variety of intermediate and light chains, and a large globular force-generating head
What is the effect on the phenotype of a cell when a member of the kinesin superfamily is absent?
The cell's microtubule network becomes disrupted, leading to changes in the cell's overall morphology.
Which of the following is a key characteristic of the 'hand-over-hand' movement mechanism of kinesin?
It enables kinesin to move processively along a microtubule for considerable distances.
What are the structural characteristics of tubulin subunits within a microtubule?
They are organized in a linear array, asymmetric, and polar with α-tubulin at one end and β-tubulin at the other.
What is the primary function of microtubule-associated proteins (MAPs)?
To increase the stability of microtubules and promote their assembly.
Which of the following statements about the microtubule-associated protein tau is correct?
An abnormally high level of phosphorylation of tau has been implicated in Alzheimer's disease.
What is one of the primary functions of microtubules in cells?
To provide mechanical support and resist forces that might compress or bend the cell.
How does the distribution of microtubules contribute to cell shape?
It determines the round, flattened shape of the cell.
What is the significance of the polar nature of microtubules?
It allows for the transport of molecules in both directions along the microtubule.
What happens to the GDP molecule after it is formed during the hydrolysis of GTP in the assembled microtubule?
The GDP molecule remains bound to the assembled polymer
What is the purpose of the nucleotide exchange from GDP to GTP during the disassembly of tubulin dimers?
It allows the dimer to serve as a building block for polymerization again
What is the structural difference between GTP-tubulin and GDP-tubulin that affects their ability to fit into a protofilament?
GTP-tubulin has a different conformation than GDP-tubulin, making it more able to fit into a protofilament
What is the role of the open sheet of tubulin-GTP subunits at the tip of the growing microtubule?
It provides a stable structure that allows the microtubule to continue growing
What is the mechanism that leads to the catastrophic shrinkage of the microtubule?
The strain from the GDP-tubulin at the plus end causes the microtubule to shrink
Which of the following is NOT a dynamic process that the cell can reorganize its actin cytoskeleton for?
Apoptosis
What is the primary function of conventional (type II) myosins?
Primary motors for muscle contraction
What is the defining characteristic of the head domain of all myosin proteins?
It contains both a site that binds an actin filament and a site that binds and hydrolyzes ATP
How do conventional (type II) myosins differ from unconventional myosins?
Conventional myosins have similar head domains but highly divergent tail domains, while unconventional myosins have similar tail domains but divergent head domains
What is the directionality of movement of conventional (type II) myosins along actin filaments?
They move toward the barbed end of the actin filament
What is the primary function of the tail domains of myosin proteins?
To anchor the myosin motor to specific cellular structures
Test your knowledge on the structure and function of microtubules. Learn about the arrangement and polarity of tubulin subunits along the protofilaments. Explore the 3D structure of the αβ-tubulin heterodimer as well as the longitudinal section of a microtubule.
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