Microtubules: Structure and Assembly

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Questions and Answers

What is the primary effect of hydrolysis on microtubules?

It promotes polymerization at the minus (-) end.

It maintains microtubule stability by enhancing the GTP cap.

It increases the length and dynamism of microtubules.

It results in longer and less dynamic microtubules. (correct)

Which factor is involved in promoting microtubule shrinkage?

Dynein

GTP cap

Tubulin

Kinesin-13 (correct)

How is the stability of a microtubule primarily maintained?

By the presence of a stable GTP cap at the plus (+) end. (correct)

By increasing the rate of tubulin dimer incorporation.

Through the action of dynein motors.

By a dynamic assembly process at the minus (-) end.

What happens if the GTP cap of a microtubule is lost?

Depolymerization ensues. (D) Signup and view all the answers

What is the relationship between hydrolysis and the structural integrity of microtubules?

Hydrolysis disrupts structural integrity leading to shrinkage. (C) Signup and view all the answers

What is the primary outcome of destabilizing MAPs on microtubules?

Shorter and more dynamic microtubules (C) Signup and view all the answers

Which condition favors the polymerization of tubulin-GTP dimers?

Higher concentration of tubulin-GTP than the hydrolysis rate (D) Signup and view all the answers

What role do microtubules play in cellular transport?

They permit transport of organelles and vesicles (D) Signup and view all the answers

What does the regulation of tubulin polymerization primarily determine?

Balance between polymerization and depolymerization (B) Signup and view all the answers

Destabilizing MAPs primarily affect which part of the microtubule structure?

Protofilaments at the ends (D) Signup and view all the answers

What happens when the concentration of tubulin-GTP dimers is lower than the hydrolysis rate?

Depolymerization occurs (D) Signup and view all the answers

Which of the following accurately describes a function of microtubules?

They support the movement of cilia and flagella (C) Signup and view all the answers

What characterizes dynamic instability in microtubules?

Rapid cycles of growth and shrinkage (A) Signup and view all the answers

What is the arrangement of the microtubule doublets in cilia and flagella?

9+2 arrangement (A) Signup and view all the answers

Which component is responsible for linking adjacent microtubule doublets?

Nexin bridges (A) Signup and view all the answers

How many protofilaments are arranged in each microtubule structure?

13 protofilaments (D) Signup and view all the answers

What type of movement is converted into bending due to the structure of microtubules?

Dynein movement (B) Signup and view all the answers

What is the basic structural composition of a microtubule?

α-tubulin and β-tubulin dimers (D) Signup and view all the answers

What is an essential characteristic of each tubulin dimer in microtubules?

Binds to GTP (A) Signup and view all the answers

What structure is formed by the arrangement of 2 central singlet microtubules?

Ciliary axoneme (A) Signup and view all the answers

What role does nexin play in the interaction of microtubules?

Prevents sliding between doublets (B) Signup and view all the answers

What is the primary role of the γ-tubulin ring complex in microtubule formation?

To initiate the formation of protofilaments (B) Signup and view all the answers

Which of the following best describes labile microtubules?

Microtubules that are dynamic and can rapidly assemble and disassemble (D) Signup and view all the answers

What is one of the main functions of stable microtubules?

Providing structural support to the cytoskeleton (D) Signup and view all the answers

Which cellular structure is identified as the site for nucleation of microtubules?

Centrosome (B) Signup and view all the answers

Which of the following statements about microtubules is FALSE?

Labile microtubules are predominantly stable in their structure. (C) Signup and view all the answers

What structural components do labile microtubules connect to?

Other cellular structures (D) Signup and view all the answers

How does the γ-tubulin ring complex contribute to microtubule function?

It initiates the assembly of protofilaments (C) Signup and view all the answers

What function does the microtubule stability primarily serve?

Establishing a rigid cell shape (B) Signup and view all the answers

What characteristic of microtubules allows them to adapt quickly to cellular needs?

Dynamic Instability (C) Signup and view all the answers

Which component is crucial for the growth of microtubules?

Tubulin-GTP (B) Signup and view all the answers

What happens to microtubules during the process described as 'shrinkage'?

They disassemble into subunits. (D) Signup and view all the answers

In the context of cellular structure, what role do microtubules primarily serve?

Providing mechanical support (A) Signup and view all the answers

What mechanism resumes growth after a shrinkage phase in microtubules?

Addition of tubulin-GTP subunits (B) Signup and view all the answers

What is the significance of dynamic instability in microtubules?

It allows rapid changes to cytoskeletal structure. (B) Signup and view all the answers

Which statement best describes the relationship between tubulin-GTP and microtubule dynamics?

Tubulin-GTP promotes growth and stability. (D) Signup and view all the answers

What describes the cyclical nature of microtubule behavior?

Growth and shrinkage form a continuous cycle. (B) Signup and view all the answers

What is the main role of motor proteins in cellular processes?

They are crucial for intracellular transport and positioning of organelles. (D) Signup and view all the answers

Which structure serves as the primary microtubule-organizing center in animal cells?

Centrosome (D) Signup and view all the answers

What occurs during the process of treadmilling in microtubules?

Tubulin dimers are added at the plus end while lost at the minus end. (D) Signup and view all the answers

What is the arrangement of microtubules in centrioles?

9 triplets of microtubules arranged in a 9+0 pattern. (C) Signup and view all the answers

What phenomenon describes the transition from microtubule polymerization to depolymerization?

Catastrophe (C) Signup and view all the answers

How do dyneins and kinesins differ in their function?

Kinesins move cargo toward the plus end while dyneins move it toward the minus end. (C) Signup and view all the answers

What can lead to depolymerization in microtubules?

Loss of the GTP cap. (A) Signup and view all the answers

Which of the following best describes the term 'MTOC'?

It is the primary site for microtubule organization. (D) Signup and view all the answers

In which type of cell is the dynamic behavior of microtubules crucial for searching chromosomes during division?

Dividing cells. (D) Signup and view all the answers

Which description best fits catastrophe in the context of microtubule dynamics?

The event causing rapid disassembly of microtubules. (C) Signup and view all the answers

What is typically the concentration relationship that leads to depolymerization?

Concentration less than GTP hydrolysis rate. (D) Signup and view all the answers

What does the term 'pericentriolar material' refer to?

The matrix surrounding the centrioles. (B) Signup and view all the answers

Which statement accurately describes the process of microtubule assembly?

Involves tubulin dimers and can be influenced by GTP availability. (C) Signup and view all the answers

Study Notes

Microtubules: Structure and Organization

Microtubules are a type of protein filament in the eukaryotic cytoskeleton
Diameter: 25nm
Hollow cylinders made of tubulin dimers
Rigid and dynamic, nucleated
Involved in intracellular transport, cell division (spindle formation), and structural support
Composed of 13 protofilaments arranged in a ring-like structure
Made of α-tubulin and β-tubulin dimers
Plus (+) end: Rapid growth, toward cell periphery
Minus (-) end: Depolymerizes rapidly, anchored to the centrosome (MTOC)
Each tubulin dimer binds to GTP for polymerization

Microtubule Assembly

Nucleation: Initiated by γ-tubulin ring complex (γ-TuRC) at the centrosome.
Polymerization: Tubulin-GTP binds, adding dimers to the protofilament. A GTP cap at the (+) end stabilizes growth. GTP on β-tubulin hydrolyzes to GDP post-assembly.
Hydrolysis: The microtubule's stability is maintained by a GTP cap at the plus (+) end. If lost, depolymerization results.

Dynamic Behavior

Microtubules show cycles of growth and shrinkage
Catastrophe: Transition from polymerization to depolymerization due to GTP cap loss.
Rescue: Growth resumes with added tubulin-GTP subunits.
Treadmilling: Addition at (+) end, removal at (-) end, maintaining constant length
Dynamic Instability: Polymerization > GTP hydrolysis rate results in polymerization; opposite for depolymerization. This allows for rapid cytoskeleton reorganization.

Microtubule-Associated Proteins (MAPs)

Stabilizing MAPS: Enhance stability, suppress depolymerization; eg, MAP2 & Tau. Result in longer, less dynamic MTs.
Destabilizing MAPS: Disrupt integrity; eg, Kinesin-13; result in shorter, more dynamic MTs.
Motor MAPS: Kinesins (toward (+) end) and Dyneins (toward (-) end) drive intracellular transport

Cilia and Flagella

Projections from the plasma membrane
Supported by microtubules
Cilia: Particle movement (e.g., mucus transport)
Flagella: Cell locomotion (e.g., sperm cells)
9 peripheral doublets (A & B microtubules)
2 central singlet microtubules
Nexin bridges connect microtubules
Dynein arms drive movement along neighboring microtubules; ATP hydrolysis is involved
Axoneme is the core structure.

Centrosome

Microtubule-organizing center (MTOC) in animal cells
Two perpendicular centrioles surrounded by pericentriolar material
Centrioles: 9 triplets of microtubules (9+0 pattern)

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Description

Dive into the fascinating world of microtubules, a crucial component of the eukaryotic cytoskeleton. This quiz covers their structure, organization, assembly processes, and roles in various cellular functions. Test your understanding of key concepts such as nucleation and polymerization.