Cell Junctions Overview
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Questions and Answers

What structural form do monomers of the major subtype of IFs take?

  • Globular clusters
  • Coiled-coil dimers (correct)
  • Tetramers in parallel
  • Linear chains

What is one of the primary roles of cell junctions?

  • Production of energy
  • Facilitation of intracellular communication
  • Prevention of molecular leakage (correct)
  • Storage of genetic material

How do dimers in major subtypes of IFs interact to form a larger structure?

  • They assemble into monomers
  • They link into staggered, antiparallel tetramers (correct)
  • They bond directly in a linear formation
  • They aggregate into spherical structures

What effect do intermediate filaments have in epithelial barriers?

<p>Assist in structural integrity and barrier function (C)</p> Signup and view all the answers

What does paracellular diffusion refer to?

<p>Movement of molecules between cells (B)</p> Signup and view all the answers

What is the primary role of the extracellular matrix (ECM) in animal tissues?

<p>Providing mechanical support to cells (C)</p> Signup and view all the answers

What distinguishes epithelial tissue from connective tissue?

<p>Epithelial tissue features dense cellular sheets. (A)</p> Signup and view all the answers

How many fibrillar proteins have been identified in animal tissues?

<p>Over 50 (D)</p> Signup and view all the answers

What are the main structural components of fibrillar proteins?

<p>N-terminal head and C-terminal tail domains (D)</p> Signup and view all the answers

Which feature is characteristic of connective tissue compared to epithelial tissue?

<p>Is ECM-rich with dispersed cells (D)</p> Signup and view all the answers

Which aspect is primarily associated with the mechanical properties of animal tissues?

<p>The presence of collagen and fibrillar proteins (A)</p> Signup and view all the answers

What is a common misconception about the relationship between animal tissues and their functions?

<p>All animal tissues have equal amounts of ECM. (D)</p> Signup and view all the answers

What role does the organization of cells into tissues have in animals?

<p>It enhances tissue-specific functions. (A)</p> Signup and view all the answers

What is the primary function of Type I-II keratins in epithelial cells?

<p>Assist in the formation of epithelial tubes (C), Support the growth of hair and nails (D)</p> Signup and view all the answers

Which type of cytoskeletal filament is primarily involved in cell adhesion through adherens junctions?

<p>Actin filaments (A)</p> Signup and view all the answers

What role does actin contraction play in tissue development?

<p>Facilitating the formation of epithelial tubes (A)</p> Signup and view all the answers

Which type of intermediate filament is found in muscle cells?

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

Vimentin is primarily found in which type of cells?

<p>Connective tissue cells (D)</p> Signup and view all the answers

What is the role of cadherins and catenins in adherens junctions?

<p>Connecting actin filaments to cell membranes (D)</p> Signup and view all the answers

Type I-II keratins are crucial in which specific cellular structure?

<p>Epithelial tubes (A)</p> Signup and view all the answers

What type of cytoskeletal structure primarily contributes to the mechanical properties of skin?

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

What is the primary role of cell junctions in tissues?

<p>Providing strong adhesion between adjacent cells under mechanical stress (D)</p> Signup and view all the answers

Which type of filament is linked by cadherins in desmosomes?

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

What is a key structural component found in desmosomes?

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

Which cell type is associated with GFAP in the context of cell junctions?

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

What does the term 'anchoring junctions' primarily refer to?

<p>Intercellular adhesion structures (D)</p> Signup and view all the answers

Which type of cadherin is primarily involved in the attachment of intermediate filaments in cells?

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

Which of the following types of filaments is NOT typically associated with desmosomes?

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

What type of intermediate filament is primarily found in neural stem cells?

<p>Nestin (D)</p> Signup and view all the answers

What is the primary function of the nuclear lamina?

<p>Signal synchronization in tissues (A)</p> Signup and view all the answers

What effect does phosphorylation have on the nuclear lamina during mitosis?

<p>It leads to lamina fragmentation (D)</p> Signup and view all the answers

What are gap junctions primarily composed of?

<p>Connexons made of connexins (B)</p> Signup and view all the answers

Which proteins bridge the nucleus and the cytoskeleton?

<p>SUN and KASH proteins (D)</p> Signup and view all the answers

Which of the following statements about gap junctions is true?

<p>They facilitate direct cell-to-cell communication. (C)</p> Signup and view all the answers

What role do linker proteins play in cells?

<p>They provide mechanical stability and adapt to stress. (D)</p> Signup and view all the answers

Which of the following is NOT a function of the nuclear lamina?

<p>Facilitating RNA processing (D)</p> Signup and view all the answers

What is the result of nuclear envelope disassembly during mitosis?

<p>Fragmentation of the nuclear lamina (C)</p> Signup and view all the answers

What primary function do hemidesmosomes serve in epithelial tissues?

<p>Link intermediate filaments to the extracellular matrix (ECM) via integrins (D)</p> Signup and view all the answers

What condition is characterized by skin blistering due to defective keratin?

<p>Epidermolysis Bullosa (D)</p> Signup and view all the answers

Which proteins are primarily associated with hemidesmosomes?

<p>α6β4 integrins and plectin (D)</p> Signup and view all the answers

What is the primary role of focal adhesions?

<p>Link actin filaments to the ECM via integrins (C)</p> Signup and view all the answers

Which type of tissue is primarily affected by mutations leading to Epidermolysis Bullosa?

<p>Epithelial tissue (C)</p> Signup and view all the answers

Which component is NOT typically found in focal adhesions?

<p>Keratin (D)</p> Signup and view all the answers

Electrical coupling is commonly associated with which type of muscle?

<p>Cardiac muscle (A)</p> Signup and view all the answers

What is the consequence of defective keratin in the context of epidermal integrity?

<p>Rupturing of the basal epidermal layer (A)</p> Signup and view all the answers

Flashcards

What are animal tissues composed of?

Animal tissues are made of organized cells connected by the extracellular matrix (ECM).

What is connective tissue?

It is a type of tissue rich in ECM, with scattered cells.

What is epithelial tissue?

It is a type of tissue with dense sheets of tightly packed cells and minimal ECM.

What is an intermediate filament (IF)?

It is a structural protein which polymerizes into long fibrous filaments. It is found in many tissues and has important roles in maintaining cell shape and structure.

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What are IFs made of?

IFs are made up of many monomers of fibrillar proteins joined end to end.

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What are the key structural features of IF proteins?

They have a central α-helical domain, a variable N-terminal head, and a variable C-terminal tail.

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How many different types of IF proteins are there?

There are over 50 different IF proteins, each with unique N-terminal and C-terminal domains.

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What is the main function of IFs?

They provide mechanical cohesion and strength to cells and tissues.

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Intermediate Filament (IF) Monomers

IF proteins are made of monomers that form coiled-coil dimers.

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IF Dimer Formation

Two IF monomers join together to form a stronger, twisted structure.

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IF Tetramer Formation

Four IF dimers assemble in a staggered and antiparallel arrangement to create a larger, more stable unit.

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IF Role in Preventing Leakage

IFs play a crucial role in preventing the leakage of molecules between cells.

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IF Role in Cell Communication

IFs help cells communicate with each other, forming a barrier against unwanted substances.

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Anchoring Junctions

Junctions that provide strong adhesion between adjacent cells, particularly under mechanical stress.

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Desmosomes

A type of anchoring junction that links intermediate filaments (e.g., keratin, desmin) of adjacent cells.

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Cadherins

A protein family that plays a crucial role in cell-cell adhesion, particularly in desmosomes.

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Cytoplasmic Plaque

A cytoplasmic plaque found in desmosomes, composed of plakoglobin and desmoplakin. It serves as a connection point for intermediate filaments and cadherins.

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GFAP (Glial Fibrillary Acidic Protein)

A type of intermediate filament found in astrocytes and glial cells, that helps maintain the structural integrity of these cells.

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Neurofilaments

A type of intermediate filament found in neurons, that helps maintain the structural integrity of neurons.

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Lamins

A type of intermediate filament found in the nuclear envelope, that helps maintain the structural integrity of the nucleus.

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Nestin

A type of intermediate filament found in neural stem cells, it plays a role in cell division and differentiation.

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Adherens Junctions

A type of cell junction that helps epithelial cells form tubes by connecting them to their neighbors.

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Keratins

Protein filaments that are part of the cytoskeleton, found in epithelial cells such as skin, hair, and nails.

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Actin Filaments

A type of protein filament found in the cytoskeleton that helps in cell movement and contraction, forming part of the adhesion belt.

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Catenins

Specific proteins that connect to actin filaments and cadherins in the cell membrane, helping to anchor the adhesion belt.

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Vimentin

A type of intermediate filament found in fibroblasts, leukocytes, and endothelial cells.

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Epithelial Tube Formation

A process where epithelial sheets form tubes by contracting actin filaments, aided by adherens junctions, cadherins, and catenins.

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Hemidesmosomes

Cell junctions that connect intermediate filaments of a cell to the extracellular matrix (ECM) via integrin proteins.

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Epidermolysis Bullosa

A group of genetic disorders characterized by blistering of the skin due to defects in keratin, a key protein in hemidesmosomes.

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Focal Adhesions

Cell junctions that link actin filaments of a cell to the ECM through integrin proteins.

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Integrins

A protein family that plays a critical role in cell-cell and cell-ECM interactions, acting as transmembrane receptors that link the cytoskeleton to the ECM.

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Plectin

A key protein in hemidesmosomes that connects intermediate filaments to integrins, supporting skin integrity.

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Electrical Coupling

The process where specialized cell junctions allow electrical signals to pass directly between adjacent cells, facilitating rapid communication.

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What is the nuclear lamina?

The nuclear lamina is a protein meshwork lining the inner surface of the nuclear envelope. It provides structural support to the nucleus and is involved in regulating nuclear processes.

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What are the key components of the nuclear lamina?

The nuclear lamina is composed of intermediate filament proteins called lamins. These proteins are assembled into a fibrous meshwork.

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How does the nuclear lamina change during mitosis?

Phosphorylation, the addition of a phosphate group, triggers the breakdown of the nuclear lamina. This is essential for nuclear envelope disassembly during mitosis, enabling chromosome separation.

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What are gap junctions?

Gap junctions are specialized cell-to-cell junctions that allow for the direct exchange of ions and small molecules between adjacent cells. This communication is crucial for coordinating cell functions.

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What are the building blocks of gap junctions?

Gap junctions are built from proteins called connexons. Each connexon is composed of six connexin subunits.

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What are linker proteins?

Linker proteins are proteins that bridge the nuclear envelope and the cytoskeleton, connecting the nucleus to the cell's structural network. These proteins are important for maintaining nuclear position and responding to mechanical stress.

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How do SUN and KASH proteins work together?

SUN proteins are embedded in the inner nuclear membrane, while KASH proteins are associated with the outer nuclear membrane. These proteins interact across the nuclear envelope, acting as molecular bridges.

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What is the role of linker proteins in cell stability?

By connecting the nucleus to the cytoskeleton, linker proteins provide support for the nucleus and contribute to the overall stability of the cell. They also enable the nucleus to respond to changes in cell shape and mechanical forces.

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Study Notes

Cell Junctions

  • Cell junctions connect animal cells in tissues
  • They facilitate intercellular communication and cohesion
  • They prevent paracellular diffusion and maintain tissue polarity
  • They play a role in epithelial barriers

Types of Cell Junctions

  • Tight Junctions:
    • Sealing proteins (claudins, occludins)
    • Involved in preventing leakage between cells
    • Connect actin filaments via cadherins
    • Important in epithelial tube formation
  • Adherens Junctions:
    • Cadherins (e.g., E-cadherin)
    • Connect actin filaments
    • Provide strong cell adhesion
    • Important for mechanical stress
  • Desmosomes:
    • Cadherins (e.g., desmoglein, desmocollin)
    • Link intermediate filaments (keratin)
    • Provide strong adhesion under stress
    • Present in tissues subject to mechanical stress e.g. skin
  • Hemidesmosomes:
    • Connect intermediate filaments to the extracellular matrix (ECM) via integrins
    • Key proteins: α6β4 integrins, plectin
  • Focal Adhesions:
    • Connect actin filaments to the ECM via integrins
    • Key proteins: integrins, talin, vinculin, α-actinin
  • Gap Junctions
    • Composed of connexons
    • Allow for electrical coupling and communication between cells
    • Important for signal synchronization (e.g. heart)

Intermediate Filaments and Cell Junctions

  • Intermediate filaments (IFs) are part of the cytoskeleton and are 10 nm in diameter
  • They are non-polarized, stable, and dynamic
  • IFs include keratin, vimentin, desmin, GFAP, neurofilaments, lamins, and nestin
  • IFs function in cell morphology maintenance
  • IFs are found peri-nuclear
  • Mutations in keratin genes can lead to diseases like epidermolysis bullosa

Cytoskeletal Intermediate Filament Structure

  • IF monomers have a central α-helical rod with N-terminal and C-terminal domains
  • Monomers form coiled-coil dimers
  • Dimers assemble into tetramers (staggered antiparallel)
  • Tetramers assemble into protofilaments
  • Eight protofilaments form a rope-like structure (intermediate filament)

Intermediate Filament Subtypes

  • Type I and II: Keratins (epithelial cells)
  • Type III: Vimentin (connective tissue), Desmin (muscle), GFAP (glia)
  • Type IV: Neurofilaments (neurons)
  • Type V: Lamins (nuclear lamina)
  • Type VI: Nestin (neurogenesis)
  • IFs are crucial for structural support and mechanical strength
  • Mutations in IF proteins can cause diseases
  • For example, Epidermolysis bullosa is a genetic disorder resulting from keratin mutations.

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Description

This quiz covers the various types of cell junctions that connect animal cells in tissues and their roles in intercellular communication and cohesion. Explore tight junctions, adherens junctions, desmosomes, and hemidesmosomes, along with their structural components and functions. Understand how these junctions maintain tissue integrity and support mechanical stress.

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