Microtubules and Their Functions in Cell Biology
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Questions and Answers

What is the primary function of labile microtubules?

  • They primarily serve to stabilize the cytoskeleton.
  • They enable intracellular transport. (correct)
  • They connect microtubules to other cellular structures. (correct)
  • They initiate nucleation at the centrosome.

Which component is responsible for the nucleation of microtubules?

  • Gamma-tubulin ring complex (correct)
  • Centrosome proteins
  • Alpha-tubulin
  • Beta-tubulin

Which statement best describes the structure of the gamma-tubulin ring complex?

  • It connects with other microtubules to enhance stability.
  • It consists of 12 subunits that facilitate protofilament assembly.
  • It is a single protein that serves as a microtubule stabilizer.
  • It is composed of 13 subunits that initiate each protofilament. (correct)

What is NOT a function associated with labile microtubules?

<p>Stabilizing the microtubule network (D)</p> Signup and view all the answers

Where does nucleation of microtubules occur?

<p>At the centrosome (B)</p> Signup and view all the answers

What characterizes labile microtubules compared to stable microtubules?

<p>Labile microtubules undergo dynamic instability. (C)</p> Signup and view all the answers

What role does the mitotic spindle play regarding microtubules?

<p>It connects chromosomes to centrioles during cell division. (A)</p> Signup and view all the answers

What is the primary role of microtubules in cancer therapy?

<p>Disrupting mitotic spindle formation to block mitosis (A)</p> Signup and view all the answers

Which statement accurately describes intermediate filaments?

<p>They provide mechanical strength and stability to cells. (A)</p> Signup and view all the answers

What structural characteristics distinguish microtubules from intermediate filaments?

<p>Microtubules are made of tubulin dimers. (D)</p> Signup and view all the answers

What effect do microtubules have on cancer cells specifically?

<p>They block mitosis and induce apoptosis in cancer cells. (B)</p> Signup and view all the answers

Which of the following best describes the dynamic nature of microtubules?

<p>They oscillate between formation and degradation based on cellular needs. (D)</p> Signup and view all the answers

What role does MAP2 play in relation to microtubules?

<p>It extends long projecting arms to space microtubules apart. (A)</p> Signup and view all the answers

What occurs at the GTP cap of microtubules?

<p>It stabilizes growth by preventing disassembly. (D)</p> Signup and view all the answers

Which statement accurately describes the structure of microtubules?

<p>Microtubules are polymers of tubulin dimers arranged in protofilaments. (C)</p> Signup and view all the answers

Which statement about tubulin-GTP binding is true?

<p>It facilitates the attachment of dimers to the (+) end of microtubules. (A)</p> Signup and view all the answers

How does Tau differ from MAP2 in terms of microtubule interaction?

<p>Tau stabilizes microtubules without affecting their spacing. (B)</p> Signup and view all the answers

What is the primary function of cilia in relation to the cell surfaces?

<p>Involved in particle movement (A)</p> Signup and view all the answers

What diameter do microtubules typically have?

<p>25 nm (A)</p> Signup and view all the answers

Which component is responsible for intracellular transport as well as supporting cell division?

<p>Microtubules (B)</p> Signup and view all the answers

Which statement regarding the active phase of cilia function is true?

<p>Dynein arms facilitate microtubule sliding (A)</p> Signup and view all the answers

What are actin filaments primarily made of?

<p>Helical polymers of actin (D)</p> Signup and view all the answers

What occurs during the recovery phase of cilia motion?

<p>Cilium returns to its original position (D)</p> Signup and view all the answers

What is a common role of microfilaments in cells?

<p>Structural support (A)</p> Signup and view all the answers

In what capacity do cilia contribute beyond particle movement?

<p>They support mucus transport (C)</p> Signup and view all the answers

What is the effect of destabilizing MAPs on microtubules?

<p>They shorten and increase the dynamics of microtubules. (A)</p> Signup and view all the answers

What initiates polymerization of microtubules?

<p>Tubulin-GTP concentration exceeding its hydrolysis rate. (B)</p> Signup and view all the answers

What regulates the balance between polymerization and depolymerization of microtubules?

<p>The concentration of tubulin-GTP dimers. (B)</p> Signup and view all the answers

How do microtubules facilitate cellular transport?

<p>By providing a pathway for organelles and vesicles. (C)</p> Signup and view all the answers

What is the consequence of having a high concentration of destabilizing MAPs?

<p>A reduction in the length and stability of microtubules. (B)</p> Signup and view all the answers

What does GTP hydrolysis rate affect in microtubule dynamics?

<p>The balance between microtubule polymerization and depolymerization. (B)</p> Signup and view all the answers

What type of microtubule dynamics is associated with increased cellular activity?

<p>Shorter, more dynamic microtubules. (A)</p> Signup and view all the answers

Which factor is NOT directly involved in regulating microtubule dynamics?

<p>Rate of vesicle transport. (D)</p> Signup and view all the answers

What process allows microtubules to rapidly reorganize in response to cellular needs?

<p>Dynamic Instability (B)</p> Signup and view all the answers

What is the role of tubulin-GTP in microtubule dynamics?

<p>It allows growth to resume. (A)</p> Signup and view all the answers

What is the key feature of microtubules that defines their behavior in cellular environments?

<p>Dynamic Instability (A)</p> Signup and view all the answers

How do microtubules respond during cellular need for rapid change?

<p>They reorganize through dynamic instability. (A)</p> Signup and view all the answers

What happens to microtubules after the addition of tubulin-GTP subunits?

<p>Growth resumes following shrinkage. (B)</p> Signup and view all the answers

In what manner does dynamic instability contribute to cellular functions?

<p>By enabling rapid adaptation and reorganization. (D)</p> Signup and view all the answers

Which statement best describes the cycles that microtubules undergo?

<p>They undergo cycles of growth and shrinkage. (C)</p> Signup and view all the answers

What is the primary structural component that microtubules are composed of?

<p>Tubulin subunits (C)</p> Signup and view all the answers

Flashcards

Microtubules

Hollow cylinders made of tubulin dimers, found in cells, involved in cell shape, movement, and division.

Mitosis

The process of cell division, resulting in two daughter cells.

Apoptosis

The process of programmed cell death, a natural mechanism to eliminate unwanted cells.

Mitotic Spindle

The structure within the cell that helps separate chromosomes during mitosis.

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Microtubule-Targeting Drugs

The process of using drugs to target microtubules, interfering with cell division and causing cancer cell death.

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Cilia

Long, hair-like projections that extend from the cell surface and beat rhythmically to move fluids or particles.

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Active phase of Ciliary motion

The process of microtubules sliding against each other, powered by dynein, to generate movement of cilia.

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Recovery phase of Ciliary motion

The return of the cilium to its original position after the active phase.

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Actin Filaments (Microfilaments)

A type of filament involved in muscle contraction, cell movement, and maintaining cell shape, made of the protein actin.

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Labile MTs

Microtubules that are rapidly assembled and disassembled, constantly changing in length and location.

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Stable MTs

Specialized microtubules that are more stable and long-lasting, responsible for maintaining cell structure.

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Microtubule nucleation

The process of forming new microtubules.

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γ-tubulin ring complex (γ-TuRC)

A protein complex that initiates microtubule nucleation by forming a ring-like structure.

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Centrosome

The cellular structure where microtubule nucleation primarily occurs.

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Intracellular transport

The process of moving molecules or organelles within the cell, often facilitated by motor proteins.

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Tubulin Dimer

α-tubulin and β-tubulin bind together, forming a two-part structure.

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Protofilament

A chain of tubulin dimers that forms the building block of microtubules.

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Microtubule Polymerization

The process of adding tubulin dimers to the (+) end of a microtubule.

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GTP Cap

GTP bound to the (+) end of a microtubule, stabilizing its growth.

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Microtubule Associated Proteins (MAPs)

Proteins that bind to microtubules, influencing their structure and stability.

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Dynamic Instability

The ability of microtubules to switch between growing and shrinking phases.

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Microtubule Growth

When a microtubule grows by adding tubulin-GTP subunits.

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Microtubule Shrinkage

The process of a microtubule losing tubulin subunits and shrinking.

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Rescue

When microtubule growth resumes after a shrinkage phase.

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Dynamic Behavior of Microtubules

Microtubules constantly growing and shrinking, allowing the cytoskeleton to respond to cellular needs.

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Destabilizing MAPs

A process that breaks apart protofilaments at the ends of microtubules, leading to shorter and more dynamic microtubules.

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Tubulin-GTP concentration

The concentration of tubulin-GTP dimers in the cytoplasm regulates whether microtubules will polymerize or depolymerize.

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Destabilizing MAPs

A type of microtubule-associated protein (MAP) that promotes the breakdown of microtubules.

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Dynamic microtubules

Microtubules can be rapidly assembled and disassembled, constantly changing in length and location.

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Microtubule transport

Microtubules are crucial for the movement of organelles, vesicles, and other cellular cargos within the cell.

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Tubulin-GTP and polymerization

The process of microtubule polymerization (growth) is favored when the concentration of tubulin-GTP dimers is higher than the rate of GTP hydrolysis.

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Study Notes

Microtubules: Structure and Function

  • Microtubules are part of the eukaryotic cytoskeleton, a network of protein filaments.
  • They are hollow cylinders, 25nm in diameter, made of tubulin dimers.
  • Microtubules are dynamic; they can grow and shrink rapidly.
  • They exhibit "dynamic instability," alternating between growth and shrinkage phases.
  • Polarity: plus (+) end grows/shrinks faster, minus (-) end is anchored to the centrosome.
  • Microtubules are involved in intracellular transport, cell division, and maintaining cell shape.
  • Microtubules have a 9+2 arrangement in cilia and flagella (9 peripheral doublets and 2 central singlets).
  • Dynein arms are motor proteins that cause sliding of microtubules to generate motion in cilia/flagella.

Microtubules in Cancer Therapy

  • Some chemotherapy drugs target microtubules.
  • Stabilizing agents (e.g., taxol) prevent microtubule depolymerization.
  • Destabilizing agents (e.g., vinca alkaloids) prevent microtubule polymerization.

Microtubule-Associated Proteins (MAPs)

  • MAPs regulate microtubule length and stability.
  • Stabilizing MAPs promote growth and prevent shrinkage.
  • Destabilizing MAPs promote shrinkage.
  • Motor MAPs drive intracellular transport (kinesin and dynein).

Microtubule Assembly

  • Microtubule assembly begins at the centrosome, with gamma-tubulin ring complexes.
  • Tubulin-GTP dimers add to the plus (+) end, forming protofilaments.
  • GTP hydrolysis and GTP cap loss lead to depolymerization.
  • Treadmilling occurs when addition and removal at opposite ends maintain constant length.

Centrosome

  • The centrosome is the main microtubule-organizing center (MTOC) in animal cells.
  • Comprised of two perpendicular centrioles surrounded by pericentriolar material.
  • Centrioles have a 9+0 arrangement of microtubule triplets.

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Description

This quiz explores the intricate functions of labile and stable microtubules, including their roles in nucleation, cancer therapy, and structural characteristics. Test your knowledge on the dynamic nature of microtubules, the function of intermediate filaments, and key proteins such as MAP2. Perfect for students studying cell biology or related fields.

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