118 Questions
What is the result of a severe desmoglein 3 deficiency?
Blistering of the skin with leakage of body fluids
Which type of intermediate filaments is found in epithelial cells?
Keratin filaments
What is the function of anchoring junctions?
To attach cells to each other or to the matrix
Which type of junctions is involved in cell-cell adhesion?
Desmosomes
What is the function of hemidesmosomes?
To attach cells to the matrix
Which protein is involved in the attachment of intermediate filaments to hemidesmosomes?
Plectin
What is the consequence of autoantibodies attacking type XVII collagen in bullous pemphigoid?
Blistering of the skin
What is the consequence of mutations in plectin?
Skin blisters associated with late-onset muscular dystrophy
What is the function of desmoglein and desmocollin?
To bind to anchor proteins and intermediate filaments
What is the result of desmosome disruption in skin autoimmune diseases like Pemphigus?
The skin epithelial cells are separated
What type of proteins are desmoglein and desmocollin?
Cadherin proteins
Where are desmosomes most abundant?
Tissues exposed to mechanical stress
What is the role of desmoplakin, plakoglobin, and plakophilin?
To link cadherin proteins to intermediate filaments
What is the purpose of desmosomes?
To hold cells together
What is the result of desmoglein and desmocollin binding to anchor proteins?
The binding of cells to intermediate filaments
Where are desmosomes found?
In many tissues, especially in skin and heart muscle
What is the main function of anchoring junctions?
To anchor cells to the extracellular matrix or to other cells
What is the role of integrins in focal adhesions?
To bind to laminin protein in the basal lamina
What is the consequence of mutations in plectin?
Skin blisters
What is the function of hemidesmosomes?
To facilitate the adhesion of cells to the basal lamina
What is the role of the cytoplasmic domain of integrins in focal adhesions?
To bind to actin filaments
What type of collagen is attacked by autoantibodies in bullous pemphigoid?
Type XVII collagen
What is the main function of desmoglein and desmocollin?
To facilitate cell-cell adhesion
What is the characteristic of hemidesmosomes?
They have a single dense plaque on the cytoplasmic surface
What is the primary function of microvilli?
To increase the surface area of the cell for absorption
What are the proteins that cross-link actin filaments in microvilli?
Fimbrin and villin
What is the characteristic of glycocalix around microvilli?
It is thicker
What is the function of cilia in epithelial cells?
To move the fluid over the surface of the cell
Where are cilia typically found in the human body?
In the upper respiratory tract and uterine tubes
What is the structure of cilia composed of?
Microtubules
What is the composition of a triplet microtubule in a basal body?
One complete microtubule and two incomplete microtubules
What is the structure that extends from the basal body into the apical cytoplasm?
Rootlet
What is the function of basal bodies in the organization of cilia and flagella?
They organize the axoneme microtubules
What is the difference between a basal body and a centriole?
Basal bodies have accessory structures such as basal foot and rootlet
What is the significance of ciliary movement during development?
It is involved in the organization of internal organs
What is the characteristic of cilia in patients with Kartagener's Syndrome?
They are immobile
What is the role of nodal cilia in development?
They help in the organization of internal organs
What is the main function of the flagellum in mammalian sperm?
To propel the sperm during fertilization
What is the characteristic of microtubules?
They are hollow tube-like structures composed of 13 protofilaments
What is the significance of the helical beating of cilia at the node?
It is responsible for the origin of left-right asymmetry
What is the main difference between flagella and cilia?
The type of movement they exhibit
What is the function of sterocilia?
They have no motility
What is the composition of protofilaments in microtubules?
Tubulin alpha and beta subunits
What is the function of the basal body in a ciliated cell?
To organize the formation of cilia and flagella
What is the structure of the axoneme in flagella and cilia?
9+2 arrangement
What is the characteristic of centrioles?
They are involved in the formation of cilia and flagella
What type of anchoring junctions are responsible for binding cells to the extracellular matrix?
Focal adhesions
What is the function of the cytoplasmic domain of integrins in focal adhesions?
Bind indirectly to actin filaments
Which protein is involved in the attachment of intermediate filaments to hemidesmosomes?
Plectin
What is the consequence of mutations in plectin?
Skin blisters
Which type of collagen is attacked by autoantibodies in bullous pemphigoid?
Type XVII collagen
What is the characteristic of hemidesmosomes?
Single dense plaque
What is the role of integrins in focal adhesions?
Bind to the extracellular matrix
What type of anchoring junctions are involved in cell-cell adhesion?
Desmosomes
What is the main role of cytoplasmic plaque proteins in desmosomes?
To provide attachment sites for intermediate filaments
Which of the following is NOT a cytoplasmic plaque protein?
Desmocollin
What is the main function of desmoplakin in desmosomes?
To provide attachment sites for intermediate filaments
Which of the following cytoplasmic plaque proteins is involved in the attachment of intermediate filaments to desmosomes?
All of the above
What is the consequence of disrupting the cytoplasmic plaque proteins in desmosomes?
Weakened cell adhesion
Which of the following proteins is involved in the attachment of cadherins to intermediate filaments?
Desmoplakin
What is the role of plakophilin in desmosomes?
To provide attachment sites for intermediate filaments
What is the function of fibrin in blood clots?
To form an elastic network
Which of the following is a characteristic of desmosomes?
They contain plaque-shaped structures on the cytoplasmic face
What is the enzyme that cleaves fibrinogen to form fibrin?
Thrombin
What is the function of von Willebrand factor in thrombus formation?
To mediate platelet adhesion
What is the site of storage of von Willebrand factor in endothelial cells?
Weibel–Palade bodies
What is the enzyme that cleaves fibrin to disperse blood clots?
Plasmin
What is the precursor molecule of plasmin?
Plasminogen
What is the function of fibrin in promoting angiogenesis?
By binding to vascular endothelial growth factor
What is the role of tissue plasminogen activator in fibrinolysis?
To activate plasminogen
What is the purpose of the plaque proteins in desmosomes?
To provide attachment sites for intermediate filaments
Which type of junctions are desmosomes?
Desmosomes are anchoring junctions
What is the role of desmoglein and desmocollin in desmosomes?
To link adjacent cells together
In which tissues are desmosomes most abundant?
Skin and heart muscle
What is the result of desmosome disruption in skin autoimmune diseases like Pemphigus?
Disruption of skin epithelial cells
What is the role of desmoplakin in desmosomes?
To provide attachment sites for intermediate filaments
What type of filaments are attached to desmosomes?
Intermediate filaments
What is the function of desmosomes in tissues?
To provide mechanical strength
What type of proteins do Integrins bind to in the basal lamina?
Laminin
What is the characteristic feature of Hemidesmosomes?
Single dense plaque on the cytoplasmic surface
Which type of intermediate filaments is attached to Hemidesmosomes?
Keratin filaments
What is the consequence of autoantibodies attacking Type XVII Collagen in Bullous Pemphigoid?
Skin blisters
Which protein is involved in the attachment of intermediate filaments to Hemidesmosomes?
Plectin
What is the function of Hemidesmosomes?
Cell-matrix adhesion
What is the structure that connects an epithelial cell to the basal lamina?
Hemidesmosome
What is the consequence of mutations in Plectin?
Muscular dystrophy with skin blisters
What is the function of desmosomes in cells?
To provide mechanical binding between adjacent cells
What type of filaments are anchored to desmosomes?
Intermediate filaments
What is the structure of a desmosome?
A button-like point of tight adhesion
What is the role of desmosomes in vertebrate development?
To form the neural tube
What is the function of adherens junctions?
To provide strong adhesion between adjacent cells
What is the role of α-catenin in adherens junctions?
To link actin filaments to cadherins
What is the structure of an adherens junction?
A complex of actin filaments, cadherins, and α-catenin
What is the function of vinculin in adherens junctions?
To anchor actin filaments to the cell membrane
What is the effect of autoantibodies attacking type XVII collagen in bullous pemphigoid?
Causing skin blisters
What is the result of a severe desmoglein 3 deficiency in the skin?
Blistering of the skin with leakage of body fluids
What is the consequence of mutations in plectin?
Skin blisters
Which type of junction is responsible for attaching epithelial cells to the basal lamina?
Hemidesmosomes
Which type of anchoring junctions are responsible for binding cells to the extracellular matrix in skin?
Focal adhesions
What is the function of integrins in hemidesmosomes?
To bind to laminin protein in the basal lamina
What is the role of integrins in focal adhesions in skin?
Binding to the extracellular matrix
What is the function of hemidesmosomes in skin?
Cell-matrix adhesion
What is the consequence of autoantibodies attacking type XVII collagen in bullous pemphigoid?
Skin blistering
Which protein is involved in the attachment of intermediate filaments to hemidesmosomes in skin?
Plectin
What is the result of mutations in plectin?
Late-onset muscular dystrophy
What is the characteristic of hemidesmosomes?
Single dense plaque on the cytoplasmic surface
What is the characteristic of hemidesmosomes in skin?
Having a single dense plaque
Which skin disease is caused by autoantibodies attacking type XVII collagen in the basal lamina?
Bullous pemphigoid
What type of intermediate filaments are involved in hemidesmosomes?
Keratin filaments
What is the function of plectin in hemidesmosomes?
To anchor intermediate filaments to hemidesmosomes
What is the result of desmosome disruption in skin autoimmune diseases like Pemphigus?
The skin epithelial cells become less adherent to each other
Which protein is responsible for the mechanical binding of cells in desmosomes?
Desmoglein
What is the characteristic of desmosomes in skin autoimmune diseases like Pemphigus?
Weaker adhesion between cells
What is the consequence of autoantibodies binding to desmosomal cadherins in Pemphigus?
The skin epithelial cells become less adherent to each other
What is the role of plaque proteins in desmosomes?
To provide attachment sites for intermediate filaments
What is the characteristic of desmosomes in tissues that are exposed to mechanical stress?
They are more abundant
What is the function of desmoplakin in desmosomes?
To provide attachment sites for intermediate filaments
What is the consequence of desmosome disruption in skin autoimmune diseases?
Skin epithelial cells become less adherent to each other
Study Notes
Anchoring Junctions
- Anchoring junctions can be subclassified according to the cytoskeletal element that is involved.
- There are two types of anchoring junctions:
- Actin filament attachment sites
- Intermediate filament attachment sites
Actin Filament Attachment Sites
- Cell-cell junction (ADHERENS JUNCTIONS)
- Cell-matrix junctions (FOCAL ADHESIONS)
Intermediate Filament Attachment Sites
- Cell-cell junctions (DESMOSOMES)
- Cell-matrix junctions (HEMIDESMOSOMES)
Desmosomes
- Strongest points of cell adhesion that provide mechanical binding
- Most abundant in tissues that are exposed to mechanical stress (epidermis of the skin, heart muscle)
- Cell-to-cell binding depends on cadherin family of proteins called desmoglein and desmocollin
- Desmosomes contain plaque-shaped structures on the cytoplasmic face of the junction, which provide attachment sites for intermediate filaments
- Plaque proteins are plakoglobins, desmoplakins, and plakophilins
- Two types of cadherins (desmoglein and desmocollin) link adjacent cells together, and cytoplasmic plaque (desmoplakin, plakoglobin, and plakophilin) links the cadherins
- Desmosomes give tissues mechanical strength
- Desmosomes are found in many tissues, especially abundant in skin (epidermis), heart muscle, and the neck of the uterus
Importance of Desmosome Junctions
- Demonstrated by some of the skin autoimmune diseases, such as PEMPHIGUS
- Affected individuals make antibodies against their own desmosomal cadherins, which bind to and disrupt the desmosomes that hold their skin epithelial cells together
Hemidesmosomes
- Resemble desmosomes morphologically
- Cell uses hemidesmosomes to attach to the basal lamina
- Cell-to-matrix adhesion proteins, such as INTEGRINS, are involved in hemidesmosomes
- Hemidesmosomes have only a single dense plaque on the cytoplasmic surface of the hemidesmosome (hemi=half) that anchors loops of intermediate filaments
- Schematic model of hemidesmosome connecting an epithelial cell to the basal lamina
- Extracellular domains of the integrins bind to laminin protein in the basal lamina, and an intracellular domain binds to an anchor protein (plectin) that binds to keratin intermediate filaments
Hemidesmosome-Related Diseases
- In a blistering skin disease called bullous pemphigoid, autoantibodies attack type XVII collagen
- Mutations in plectin cause skin blisters associated with late-onset muscular dystrophy
Focal Adhesions
- Bind the cells to the extracellular matrix
- Cell-to-matrix adhesion proteins, such as INTEGRINS, are responsible for the binding to the matrix
- Cytoplasmic domain of the integrin binds indirectly to actin filaments
- Integrin's extracellular domains bind to components of the extracellular matrix, while the cytoplasmic tail of the β subunit binds indirectly to actin
Microvillus Structure
- A bundle of parallel actin filaments extend 0.5μ down into the apical cytoplasm and enter into the terminal web
- Actin filaments are cross-linked into closely packed bundles by actin-bundling proteins, villin, and fimbrin, forming the core of a microvillus
- Actin filaments are attached to the plasma membrane by lateral arms consisting of myosin I and calmodulin
- Glycocalix is thicker around the microvilli, forming a striated border, and is PAS+
Cilia and Flagella
- Cilia are eyelash or hair-like processes from the cell surface, motile, and longer than microvilli (5-10μ long, 0.2μ in diameter)
- Under the electron microscope, they have a complex internal structure composed of microtubules
- 250 or more cilia are found in each cell, arranged in parallel rows, and function to move fluid over the surface of the cell
- Found in epithelial cells of the upper respiratory tract, uterine tubes (oviducts), and efferent ducts (Ductus efferentes)
Basal Body Structure
- At the base of a cilium, a central pair of single microtubules terminates
- Each of the peripheral doublets is continuous with a triplet microtubule of the basal body
- Three microtubules are fused together and form a triplet microtubule
- Basal body resembles a centriole but contains some accessory structures such as basal foot and rootlet
Cilia Function
- Ciliary movement is important during development
- Dynein arms are absent from cilia in patients with Kartagener's Syndrome
- Nodal Cilia cannot move during development, and internal organs cannot be located at their normal positions
- Helical beating of cilia at the node, and the origins of left-right asymmetry
Flagella Structure and Function
- Flagellum propels sperm, is longer than cilia (100-200 μ), and has the same internal structure as cilia (Axoneme 9+2)
- Has a different type of movement (undulating wave type of movement) and is less in number (one or two in a single cell)
- Mammalian spermium contains 9 additional dense fibers around the axoneme (9+9+2), which serves a protective function
Microtubule Structure
- Microtubules are hollow tube-like or pipe-like structures
- The wall of the microtubule is composed of 13 protofilaments
- Protofilaments are composed of Tubulin subunits (dimer), which consist of Tubulin α and Tubulin β
Gap Junctions
- Site of firm adhesion of cells
- Allow free interchange of substances
- Important role in regulation of intrauterine development and differentiation
- Coordinate function among groups of cells
Anchoring Junctions
- Two types: Hemidesmosomes and Focal Adhesions
Hemidesmosomes
- Have a single dense plaque on the cytoplasmic surface
- Anchor loops of intermediate filaments
- Integrins bind to laminin protein in the basal lamina
- Intracellular domain binds to an anchor protein (plectin) that binds to keratin intermediate filaments
- Found in epithelial cells, attach to basal lamina
- Mutations in plectin cause skin blisters
- Autoantibodies attack type XVII collagen in bullous pemphigoid, a blistering skin disease
Focal Adhesions
- Bind cells to the extracellular matrix
- Cell-matrix adhesion proteins; integrins responsible for binding to the matrix
- Cytoplasmic domain of the integrin binds indirectly to actin filaments
- Integrin's extracellular domains bind to components of extracellular matrix
- Cytoplasmic tail of the β subunit binds indirectly to actin
Adhesion Proteins
- Fibrin: a major ECM component of blood clots
- Forms an elastic network to which cells and other ECM components bind
- Polymerization of fibrin to form the network occurs when its precursor molecule fibrinogen is cleaved by the enzyme thrombin
- Fibrin has binding interactions with various extracellular components, including fibronectin, heparin, growth factors, and cytokines
- Fibrinolysis is mediated by plasmin, which cleaves fibrin
Von Willebrand Factor
- Plays a key role in the major response of platelets to vascular injury by mediating the initiation and progression of thrombus formation
- Enables cell adhesion to develop by forming a bridge between collagen in the vessel wall and blood platelets
Desmosomes
- Strongest points of cell adhesion that provide mechanical binding
- Most abundant in tissues that are exposed to mechanical stress (epidermis of the skin, heart muscle)
- Cell-to-cell binding depends on cadherin family of proteins called desmoglein and desmocollin
- Contain plaque-shaped structures on the cytoplasmic face of the junction which provide attachment sites for intermediate filaments
- Plaque proteins are plakoglobins, desmoplakins, and plakophilins
- Found in many tissues, especially abundant in skin, heart muscle, and the neck of the uterus
- Importance of desmosome junctions is demonstrated by some skin autoimmune diseases, such as pemphigus, where affected individuals make antibodies against their own desmosomal cadherins
Desmosomes
- Strongest points of cell adhesion that provide mechanical binding
- Most abundant in tissues exposed to mechanical stress (epidermis of the skin, heart muscle)
- Contain plaque-shaped structures on the cytoplasmic face of the junction, providing attachment sites for intermediate filaments
- Plaque proteins include plakoglobins, desmoplakins, and plakophilins
- Two types of cadherins (desmoglein and desmocollin) link adjacent cells together
- Cytoplasmic plaque (desmoplakin, plakoglobin, and plakophilin) links the cadherins to intermediate filaments
Importance of Desmosomes
- Desmosomal cadherins are targeted in autoimmune diseases such as Pemphigus, leading to blistering of the skin
- Affected individuals make antibodies against their own desmosomal cadherins, disrupting desmosomes and causing skin epithelial cells to separate
Intermediate Filaments
- Types of intermediate filaments include keratin filaments in epithelial cells and desmin filaments in heart and muscle cells
- Intermediate filaments can be subclassified according to the cytoskeletal element involved
Anchoring Junctions
- Subclassified into two types:
- Intermediate filament attachment sites
- Cell-cell junctions (desmosomes)
- Cell-matrix junctions (hemidesmosomes)
- Actin filament attachment sites
- Cell-cell junctions (adherens junctions)
- Cell-matrix junctions (focal adhesions)
- Intermediate filament attachment sites
Hemidesmosomes
- Resemble desmosomes morphologically
- Cell uses hemidesmosomes to attach to the basal lamina
- Contain a single dense plaque on the cytoplasmic surface that anchors loops of intermediate filaments
- Schematic model shows an epithelial cell attached to the basal lamina via hemidesmosomes
- Autoantibodies attack type XVII collagen in bullous pemphigoid, a blistering skin disease
- Mutations in plectin cause skin blisters associated with late-onset muscular dystrophy
Adherens Junctions
- Actin filament bundles are attached by intracellular anchor proteins to cadherins
- Cadherins are transmembrane proteins that bind to those of adjacent cells, tying actin filament bundles together
- Adherens junctions in the form of adhesion belts between epithelial cells in the small intestine
- Role in early development: controlled contraction of actin filament bundles causes epithelial cells to narrow and form a tube in vertebrate development
Anchoring Junctions
- Anchoring junctions can be subclassified according to the cytoskeletal element involved
- Two types of anchoring junctions:
- Actin filament attachment sites
- Cell-cell junctions (ADHERENS JUNCTIONS)
- Cell-matrix junctions (FOCAL ADHESIONS)
- Intermediate filament attachment sites
- Cell-cell junctions (DESMOSOMES)
- Cell-matrix junctions (HEMIDESMOSOMES)
- Actin filament attachment sites
Desmosomes
- Desmosomes are strongest points of cell adhesion that provide mechanical binding
- Most abundant in tissues that are exposed to mechanical stress (Epidermis of the skin, heart muscle)
- Cell to cell binding depends on cadherin family of proteins called desmoglein and desmocollin
- Desmosomes contain plaque-shaped structures on the cytoplasmic face of the junction which provide attachment sites for intermediate filaments
- Plaque proteins: plakoglobins, desmoplakins, plakophilins
Hemidesmosomes
- Hemidesmosomes resemble desmosomes morphologically
- Hemidesmosomes have only a single dense plaque on the cytoplasmic surface of the hemidesmosome (hemi=half) that anchors loops of intermediate filaments
- Hemidesmosomes connect epithelial cells to the basal lamina
- Integrin (α6β4) and type XVII collagen (also called BPAG2) attach to the basal lamina
Importance of Desmosomes and Hemidesmosomes
- In a blistering skin disease called bullous pemphigoid, autoantibodies attack type XVII collagen
- Mutations in plectin cause skin blisters associated with late-onset muscular dystrophy
- Cataract, heart malformations, and skin blistering are examples of diseases related to desmosome and hemidesmosome dysfunction
This quiz covers the basics of intermediate filaments and anchoring junctions in cells, including types of filaments and their locations in different cell types.
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