Cytoskeleton and Microtubules in Cell Biology

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Questions and Answers

What role do CLASP proteins serve in relation to microtubules?

They initiate microtubule catastrophe.

They enhance microtubule disassembly.

They rescue microtubules from catastrophe. (correct)

They stabilize microtubules by preventing polymerization.

Where are the minus ends of microtubules typically anchored?

At the nucleus.

In the centrosome. (correct)

In the cell membrane.

At the cell periphery.

What distinctive feature do stable microtubules in nerve cells possess?

They terminate in the cytoplasm rather than being anchored. (correct)

They have orientation that varies in direction.

They are anchored at both ends in the centrosome.

They are exclusively formed during mitosis.

What is the primary direction of vesicle transport mediated by plus-end–directed kinesins?

Toward the cell periphery. Signup and view all the answers

Which statement accurately describes the function of dynein and kinesin I?

They serve opposite transport functions on microtubules. Signup and view all the answers

What is the primary role of the cytoskeleton in the context of cell movement?

Generating forces for movement and positioning organelles Signup and view all the answers

Which process indicates that GTP hydrolysis affects microtubule stability?

Dynamic instability of microtubules Signup and view all the answers

What occurs at the plus end of the microtubule during its growth phase?

GTP-bound tubulin dimers associate Signup and view all the answers

Which statement best describes the dynamic instability of microtubules?

Growth and shrinkage are dependent on GTP cap retention. Signup and view all the answers

What is the effect of depolymerases on microtubules?

They initiate shrinkage by removing GTP-tubulin from the plus end. Signup and view all the answers

What structural component is unique to motile cilia compared to primary cilia?

The presence of a central pair of microtubules Signup and view all the answers

Which of the following components is responsible for the sliding motion of interpolar microtubules during anaphase B?

Plus-end-directed motor proteins Signup and view all the answers

How are the outer microtubule doublets in cilia juxtaposed to the central pair of microtubules?

Joined by nexin links and radial spokes Signup and view all the answers

Which type of microtubule is directly responsible for attaching to kinetochores during cell division?

Kinetochore microtubules Signup and view all the answers

What mechanism drives chromosome movement towards the spindle poles during anaphase A?

Depolymerization and shortening of microtubules Signup and view all the answers

What is the primary role of astral microtubules in cell division?

Driving the separation of spindle poles Signup and view all the answers

Which of the following correctly describes intermediate filaments (IFs)?

They are flexible and help cells endure physical stress. Signup and view all the answers

How do dynein and kinesin I differ in their functional directionality?

Dynein moves towards the minus end, while kinesin I moves towards the plus end. Signup and view all the answers

What type of cellular structure do desmosomes involve, and how do they relate to intermediate filaments?

They serve as contact points between epithelial cells linked via intermediate filaments. Signup and view all the answers

What is the structural assembly order of intermediate filaments starting from the polypeptide level?

Polypeptides assemble to form tetramers, then protofilaments, followed by filaments. Signup and view all the answers

Study Notes

Cytoskeleton and Cell Motility

The cytoskeleton is a dynamic scaffold providing structural support to the cell.
It acts as a framework for positioning organelles.
It's a network of tracks directing the movement of materials (organelles, vesicles, mRNA).
It's involved in generating force for cell movement.
The cytoskeleton is essential for cell division machinery.
The cytoskeleton is composed of microfilaments, microtubules, and intermediate filaments.

Microtubules: Structure and Dynamic Instability

Microtubules are hollow tubes made of tubulin dimers (α-tubulin and β-tubulin).
Microtubules exhibit dynamic instability, alternating between growth and shrinkage phases.
Microtubule growth is initiated by the addition of tubulin dimers to the plus end.
GTP hydrolysis regulates microtubule stability; GTP-bound tubulin is more stable than GDP-bound tubulin.
Microtubule-associated proteins (MAPs) regulate microtubule organization and stability.
Polymerase increases the incorporation of GTP-bound tubulin.
Depolymerases remove GTP-bound tubulin.
CLASP proteins rescue microtubules from catastrophe.

Microtubule Organization

Minus ends of microtubules are anchored in the centrosome (an MTOC).
In interphase cells, the centrosome is located near the nucleus, and microtubules extend outward to the cell periphery.
During mitosis, duplicated centrosomes separate and microtubules reorganize to form the mitotic spindle.
Centrosomes consist of pericentriolar material surrounding a pair of centrioles. Microtubules radiate from this material.

Microtubule-Based Cilia and Flagella

Cilia and flagella are microtubule-based structures involved in cell movement.
Primary cilia and motile cilia are anchored in basal bodies, containing nine triplets of microtubules.
The axoneme of motile cilia includes an additional central pair of microtubules, radial spokes, and dynein arms.

Microtubule Motor Proteins

Dynein and kinesin move along microtubules in opposite directions.
The globular head domains of the heavy chains bind microtubules, and serve as motor domains of the molecule.
Light chains bind to cargo (e.g., vesicles).

Transport of Vesicles

Kinesin I moves vesicles and organelles along microtubule plus ends, while dynein moves them along minus ends.
The direction of transport corresponds to the direction of microtubule extension.

Association of Endoplasmic Reticulum

The endoplasmic reticulum (ER) appears closely correlated with microtubules in epithelial cells.

Intermediate Filaments (IFs)

IFs are flexible, rope-like fibers providing mechanical strength.
IFs include keratin, desmin, vimentin, and lamins.
IFs are a diverse family of proteins.
IFs are crucial in providing support and resisting mechanical stress, especially in muscle cells, neurons, and epithelia.

Attachment to Desmosomes and Hemidesmosomes

Desmosomes are cell-to-cell junctions involving intermediate filaments.
Hemidesmosomes are cell-to-ECM junctions involving intermediate filaments.

Extracellular Matrix (ECM)

The ECM has three main components: structural proteins (collagen), polysaccharides (GAGs and Proteoglycans), and adhesion proteins (fibronectin, laminin).
The ECM plays a vital role in cells.

Collagen Structure and Function

Collagen is a triple helix composed primarily of glycine, proline, and hydroxyproline
Protein cross-links are crucial in the strength and stability of collagen.
Type IV collagen is a key component of basal laminae

Type IV Collagen and Basal Lamina

Type IV collagen forms networks, unlike other collagens which form fibrils.
Crucial component of basal lamina.

Proteoglycans

Proteoglycans are GAGs covalently linked to a core protein molecule.

Integrins

Integrins are major receptors responsible for cell attachment to the ECM.
Connect the ECM to the cytoskeletal filaments.

Cell-Matrix Junctions

Integrins mediate focal adhesions and hemidesmosomes, crucial for cell attachment.

Functions of Cytoskeleton

Golgi localization.

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Description

Explore the fundamental roles of the cytoskeleton in providing structural support and facilitating cell motility. This quiz covers the various components of the cytoskeleton, focusing on microtubules and their dynamic behavior, including stability and organization. Test your understanding of these key cellular structures!