Actin Filaments in Cell Division and Junctions

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Questions and Answers

What is the function of actin filaments in the cell-to-cell junctions?

Generating force for cell migration

Forming microtubules in the cytoskeleton

Forming the contractile ring during mitosis and meiosis

Attaching to the cytoplasmic domain of transmembrane protein called cadherins (correct)

What is the process involved in cell motility?

Depolymerization of actin filaments at the leading edge

Formation of focal adhesions with the extracellular matrix

Formation of microtubules in the cytoskeleton

Actin polymerization and formation of protrusions at the leading edge (correct)

What are the components of the focal adhesion?

Microtubules, intermediate filaments, and microfilaments

Cytoplasmic domain: Microtubules, Transmembrane proteins: Cadherins, Extracellular components: Collagen

Cytoplasmic domain: Actin filaments, Transmembrane proteins: Integrins, Extracellular components: Laminin and fibronectin (correct)

Cytoplasmic domain: Intermediate filaments, Transmembrane proteins: Occludins, Extracellular components: Fibronectin

What is the function of occludins and claudins?

Traversing the outer leaflets of the cells and interdigitating with occludins and claudins of the neighboring cell Signup and view all the answers

What is the function of actin filaments during mitosis and meiosis?

Forming the contractile ring that separates the two daughter cells Signup and view all the answers

What is the process involved in depolymerization of actin filaments?

Depolymerization of actin filaments at the trailing edge Signup and view all the answers

What is the primary function of intermediate filaments in cells?

To enable cells to withstand mechanical stress Signup and view all the answers

What is the characteristic size of intermediate filaments?

10 nm in diameter Signup and view all the answers

What is the arrangement of monomers in the formation of intermediate filaments?

Helical monomers assemble into antiparallel tetramers Signup and view all the answers

Where are intermediate filaments often anchored to the plasma membrane?

At cell-to-cell junctions Signup and view all the answers

What is the characteristic of intermediate filament protein subunits?

They are divers and tissue-specific Signup and view all the answers

What is the arrangement of dimers in the formation of intermediate filaments?

Two dimers line up to form a staggered tetramer Signup and view all the answers

What is the primary function of microtubule organizing centers?

To facilitate the polymerization of tubulins Signup and view all the answers

What is the main difference between centrosome and basal bodies?

Location in the cell Signup and view all the answers

What is the primary function of microtubules in eukaryotic cells?

To provide the tracks for intracellular transport Signup and view all the answers

What is the role of gamma-tubulin ring complex in centrosome?

To nucleate microtubules Signup and view all the answers

What is the significance of determining the type of intermediate filaments in a tumor cell?

To identify the cell type from which the cancer originated Signup and view all the answers

What is the direction of movement of kinesin motor proteins?

Toward the plus (+) end of microtubules Signup and view all the answers

What is the role of microtubule-associated proteins (MAPs) in regulating microtubule dynamics?

To regulate the rate of microtubule growth Signup and view all the answers

What is the characteristic feature of microtubules that allows them to grow and shrink?

Dynamic instability, with rapid growth and shrinkage Signup and view all the answers

How does herpes virus infect cells?

By using dynein to move towards the nucleus Signup and view all the answers

What is the function of the (-) minus end of microtubules?

To cap the microtubule and prevent depolymerization Signup and view all the answers

What is the energy source used by microtubule-associated motor proteins?

ATP Signup and view all the answers

What is the significance of the orientation of microtubule assembly?

To determine the direction of microtubule growth Signup and view all the answers

What is the function of microtubules in cell division?

Formation of the mitotic spindle Signup and view all the answers

What is the effect of 2019-nCoV on the cilia?

Damaging effect on the organization of cilia Signup and view all the answers

What is the function of minus ends of microtubules?

Attach to the centrosome Signup and view all the answers

What is the role of centrosome in cell division?

Doubling before mitosis Signup and view all the answers

What is the effect of microtubules on chromosome movement?

Elongation and shortening of microtubules Signup and view all the answers

What is the stage of the cell cycle where microtubules undergo a dramatic change in arrangement?

Throughout the cell cycle Signup and view all the answers

Study Notes

Actin Filaments

Form the contractile ring that separates the two daughter cells at mitosis and meiosis
Involved in cell-to-cell junctions, specifically in zonula occludens (tight junction) and zonula adherens junction
Attach to occludin or claudin transmembrane proteins via ZO-1 proteins in tight junctions
Attach to the cytoplasmic domain of transmembrane protein called cadherins in adherens junctions
Involved in focal adhesions, which are dynamic attachments that attach cells to extracellular matrix proteins
Necessary for cell motility/crawling, which involves three interrelated processes: actin polymerization, formation of protrusions, and depolymerization of actin filaments

Intermediate Filaments

The toughest and most stable component of the cytoskeleton
Do not undergo polymerization-depolymerization
About 10 nm in diameter, intermediate in size between actin microfilaments and thicker myosin of smooth muscle cells
Main function is to enable cells to withstand mechanical stress
Form a network throughout the cytoplasm and extend out to the cell periphery
Often anchored to the plasma membrane at cell-to-cell junctions
Prominent in cells that are subject to mechanical stress, such as nerve cells, muscle cells, and epithelial cells

Microtubule Organizing Center (MTOC)

A nucleating site responsible for the polymerization of tubulins
Two types: Centrosome and Basal bodies

Centrosome

The dominant form of MTOC, found in most cells
Located on the side of the nucleus in non-dividing cells
Composed of two short cylindrical structures called centrioles, which are at right angle to each other
Surrounded by a cloud of proteins called Pericentriolar material
Each centriole has nine triplets of microtubules

Microtubules

Found in the cytoplasm of all eukaryotic cells
Long hollow tubes, 25 nm in outer diameter
Subunits are heterodimers of alpha (α) tubulin and beta (β) tubulin
Function: Provide the “tracks” for intracellular transport, form cilia and flagella, and form the mitotic spindle
Orientation of assembly gives a (+) plus and (-) minus ends
Highly dynamic in length, with MTs growing and shrinking by the addition or loss of tubulin heterodimers at the + end
The rate of microtubule growth is regulated by microtubule-associated proteins (MAPs)
Involved in the transportation of vesicles and organelles within the cell, using microtubule-associated motor proteins such as kinesin and dynein
Used by some viruses, such as herpes virus, to get from the plasma membrane to the nuclear envelope during infection

Clinical Correlation: Intermediate Filaments

The type of cytoplasmic intermediate filaments produced by cells in a tumor can tell the tissue type of origin of the tumor
Used by pathologists to identify the tissue of origin of a tumor cell that may have metastasized

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Description

Explore the role of actin filaments in cell division, including the formation of the contractile ring during mitosis and meiosis, and their function in cell-to-cell junctions. Learn about their location and importance in epithelial cells.