Cytoskeleton: Actin, Microtubules, Intermediate Filaments

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Questions and Answers

What is the primary structure of microtubules?

Two chains forming a helix

Flexible strands composed of actin and myosin

Thick fibers made of various proteins

Hollow tubes composed of α- and β-tubulin dimers (correct)

Which cytoskeletal component directly mediates cell motility through actin-myosin interactions?

Mitochondrial tracks

Intermediate filaments

Actin filaments (correct)

Microtubules

What role do Rho-GTPases play in cellular motility?

They promote the disassembly of focal adhesions.

They direct the orientation of actin fibers in the cytoskeleton.

They are involved in the formation of actin filaments.

They regulate adhesion and protrusion during migration. (correct)

What is the role of microtubules in relation to vesicular transport?

They provide tracks for vesicular transport facilitated by kinesin and dynein. Signup and view all the answers

Cellular polarity is crucial for which of the following processes?

Guiding directional movement and migration. Signup and view all the answers

Which mediator is involved in the polymerization of actin filaments?

ARP2/3 complex Signup and view all the answers

What is the primary function of focal adhesions during cell migration?

Providing traction and anchoring to the extracellular matrix. Signup and view all the answers

What distinguishes intermediate filaments from actin filaments and microtubules in terms of cell motility?

Intermediate filaments do not participate directly in motility. Signup and view all the answers

Which of the following best describes the role of protrusions in cell motility?

They are essential for the initial stages of cell movement. Signup and view all the answers

Which of the following options directly influences the assembly of microtubules?

Binding of GTP to tubulin dimers Signup and view all the answers

What effect does tension have on focal adhesions?

It leads to an increase in focal adhesion size and strength. Signup and view all the answers

In terms of cell structure support, which of the following accurately describes the function of actin filaments?

They provide mechanical support and maintain the cell shape. Signup and view all the answers

Which of the following is NOT a known role of microtubules?

Providing tensile strength to the cell Signup and view all the answers

What contributes to the increased variation in microtubule behavior when utilizing tubulin isoforms?

Multiple gene-encoded isoforms of both α- and β-tubulin Signup and view all the answers

What is the primary structural unit of microtubules?

Heterodimers of α- and β-tubulin Signup and view all the answers

How do post-translational modifications (PTMs) influence microtubules?

They enhance heterogeneity and regulate microtubule behavior. Signup and view all the answers

Which factor is NOT associated with the dynamics of tubulin isoforms?

Inter-organismal genetic transfer Signup and view all the answers

What structural arrangement is caracteristic of stress fibers in cells?

Antiparallel arrays associated with myosin II Signup and view all the answers

Which type of microtubule organization is typically found in dividing cells?

Radial protrusions Signup and view all the answers

What is the main function of the cortical networks generated by actin structures?

Exert tension in all directions Signup and view all the answers

What consequence can mutations in TubB isoforms have?

Brain malformations due to tubulinopathies Signup and view all the answers

Which statement about the role of actin in generating cell geometry is correct?

Actin exerts a protrusive force enabling cell shape and movement. Signup and view all the answers

What feature distinguishes non-radial arrays of microtubules?

They are typically associated with differentiated non-dividing cells. Signup and view all the answers

What is the primary function of stress fibers in elongated cells?

Providing rigidity and structural integrity Signup and view all the answers

Which components are primarily responsible for generating contractile forces in cells?

Actin and myosin interactions Signup and view all the answers

How does the actin cortex contribute to cell behavior during migration?

By regulating cortical tension and enabling shape changes Signup and view all the answers

What structural role do actin and myosin play in morphogenesis?

They form contractile arrays essential for shape changes Signup and view all the answers

Which of the following best describes a lamellipodium?

A broad, flat protrusion facilitating forward movement Signup and view all the answers

What is the function of filopodia in cell migration?

Acting as sensory structures to explore the environment Signup and view all the answers

Where does the remodeling of tissue primarily occur in epithelial elongation?

Within the plane of the tissue Signup and view all the answers

What is the primary role of a uropod in migrating cells?

Helping in retraction and maintaining polarity during movement Signup and view all the answers

Which cellular projection is characterized by tightly bundled actin filaments?

Filopodia Signup and view all the answers

What defines the primary function of microtubules in epithelial morphogenesis?

Supporting cell shape changes and mechanical properties Signup and view all the answers

What is the primary role of podosomes in cells?

Facilitating cell adhesion and mechanosensing Signup and view all the answers

Which cellular structures are primarily responsible for increasing surface area for absorption?

Microvilli Signup and view all the answers

What initiates the nucleation of actin filaments during cell migration?

The activation of the Arp2/3 complex Signup and view all the answers

During mesenchymal migration, what occurs immediately after actin nucleation?

Cell polarization towards direction Signup and view all the answers

Which statement accurately describes the role of stress fibers in cell movement?

They help in the contractile phase of cell movement. Signup and view all the answers

What is a key feature of lamellipodia during cell migration?

They provide compressive resistance. Signup and view all the answers

What occurs during the final stages of cell migration?

The disassembly of focal adhesions from the rear. Signup and view all the answers

How do protrusions like lamellipodia and filopodia drive cell migration?

By exploring the environment and providing directional movement. Signup and view all the answers

Which process involved in the formation of cellular protrusions is crucial for rearranging components?

Increased protease activity. Signup and view all the answers

What type of actin structure is primarily associated with cell adhesion during migration?

Podosomes Signup and view all the answers

Study Notes

Cytoskeleton Overview

Composed of three main components: Microtubules, Actin filaments, and Intermediate filaments.
Provides rigidity, flexibility, shape, and structural support to the cell.
Plays a critical role in cell movement, migration, division, and organizational reformation.

Comparison of Cytoskeletal Elements

Structure

Actin Filaments: Composed of two chains in a helical structure, predominantly made of actin and myosin.
Microtubules: Hollow structures formed from α- and β-tubulin dimers, typically anchored at the centrosome.
Intermediate Filaments: Diverse, thick structures made of various proteins (keratins, vimentin), lacking inherent polarity.

Role in Cell Shape and Organization

Actin Filaments: Provide mechanical support, maintain cell shape, and are involved in muscle contraction and cell division (cytokinesis).
Microtubules: Organize internal cell structure, position organelles, and form mitotic spindle during division. Essential for vesicular transport.
Intermediate Filaments: Provide tensile strength and reinforce cell shape.

Role in Cell Motility and Migration

Actin Filaments: Form lamellipodia and filopodia, critical for cell movement and shape changes through actin-myosin interactions.
Microtubules: Facilitate vesicular trafficking and centrosome positioning. Integral to cilia and flagella for cell motility.
Intermediate Filaments: Do not contribute directly to motility but maintain organelle positioning and structural integrity.

Mechanisms of Assembly

Actin Filaments: Assembly is ATP-dependent; involves nucleation and branching, with actin hydrolysis leading to fiber shortening.
Microtubules: GTP-dependent assembly; GTP binding promotes growth, hydrolysis releases dimers.
Intermediate Filaments: Assembly mechanisms are diverse due to varied protein compositions.

Mediators of Assembly

Actin Filaments: Nucleation is mediated by ARP2/3 complex and NPFs.
Microtubules: Assembly guided by isoform patterns of tubulin.

Variation in Microtubule Heterodimers

Multiple Tubulin Isoforms: Various gene-encoded isoforms of α- and β-tubulin influence microtubule function.
Post-translational Modifications (PTMs): PTMs enhance protein diversity and regulate behavior, affecting stability and interactions.
Mutations: Alterations can impact growth, stability, and lead to tubulinopathies.

Actin Arrangements and Cell Geometry

Microtubule Organization: Varies by cell type; cells can possess radial or non-radial arrangements influencing internal structure and dynamics.
Actin Structures:
- Branched and Bundled Actin: Provide compressive resistance and protrusive forces.
- Cortical Networks: Generate tension in multiple directions, maintaining cell integrity.
- Stress Fibers: Contractile bundles that contribute to rigidity and migration by connecting to focal adhesions, utilizing actin-myosin interactions.

Steps in Formation of Cell Protrusions

Cell Migration Steps:
- Signal pathway activation followed by actin nucleation.
- Establish cell polarity and frontal protrusions (e.g., lamellipodium).
- Form focal adhesions that generate forces necessary for cell movement and retraction.

Key Features of Protrusions, Polarity, and Focal Adhesions

Protrusions: Actin-driven extensions (lamellipodia and filopodia) facilitate migration and environmental interaction.
Cellular Polarity: Directs cytoskeletal organization, ensuring directional migration.
Focal Adhesions: Multi-protein complexes linking the cytoskeleton to the extracellular matrix, vital for anchoring and transmitting mechanical signals.

Cytoskeletal Cross-talk in Migration

Forces of Migration:
- Polarization: Establishes directionality for movement.
- Protrusion: Initiates movement via actin polymerization.
- Adhesion: Provides traction through integrin-mediated attachment.
- Retraction: Facilitates forward movement by releasing adhesions at the rear.

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Description

This quiz explores the differences and similarities between actin filaments, microtubules, and intermediate filaments. You'll examine their structures, roles in cell shape, motility, assembly mechanisms, and the mediators involved in these processes. Perfect for understanding cell organization and function.