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?

Assist in structural integrity and barrier function Signup and view all the answers

What does paracellular diffusion refer to?

Movement of molecules between cells Signup and view all the answers

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

Providing mechanical support to cells Signup and view all the answers

What distinguishes epithelial tissue from connective tissue?

Epithelial tissue features dense cellular sheets. Signup and view all the answers

How many fibrillar proteins have been identified in animal tissues?

Over 50 Signup and view all the answers

What are the main structural components of fibrillar proteins?

N-terminal head and C-terminal tail domains Signup and view all the answers

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

Is ECM-rich with dispersed cells Signup and view all the answers

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

The presence of collagen and fibrillar proteins Signup and view all the answers

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

All animal tissues have equal amounts of ECM. Signup and view all the answers

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

It enhances tissue-specific functions. Signup and view all the answers

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

Assist in the formation of epithelial tubes Signup and view all the answers

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

Actin filaments Signup and view all the answers

What role does actin contraction play in tissue development?

Facilitating the formation of epithelial tubes Signup and view all the answers

Which type of intermediate filament is found in muscle cells?

Desmin Signup and view all the answers

Vimentin is primarily found in which type of cells?

Connective tissue cells Signup and view all the answers

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

Connecting actin filaments to cell membranes Signup and view all the answers

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

Epithelial tubes Signup and view all the answers

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

Keratins Signup and view all the answers

What is the primary role of cell junctions in tissues?

Providing strong adhesion between adjacent cells under mechanical stress Signup and view all the answers

Which type of filament is linked by cadherins in desmosomes?

Intermediate filaments Signup and view all the answers

What is a key structural component found in desmosomes?

Plakoglobin Signup and view all the answers

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

Astrocytes Signup and view all the answers

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

Intercellular adhesion structures Signup and view all the answers

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

Desmoglein Signup and view all the answers

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

Microtubules Signup and view all the answers

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

Nestin Signup and view all the answers

What is the primary function of the nuclear lamina?

Signal synchronization in tissues Signup and view all the answers

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

It leads to lamina fragmentation Signup and view all the answers

What are gap junctions primarily composed of?

Connexons made of connexins Signup and view all the answers

Which proteins bridge the nucleus and the cytoskeleton?

SUN and KASH proteins Signup and view all the answers

Which of the following statements about gap junctions is true?

They facilitate direct cell-to-cell communication. Signup and view all the answers

What role do linker proteins play in cells?

They provide mechanical stability and adapt to stress. Signup and view all the answers

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

Facilitating RNA processing Signup and view all the answers

What is the result of nuclear envelope disassembly during mitosis?

Fragmentation of the nuclear lamina Signup and view all the answers

What primary function do hemidesmosomes serve in epithelial tissues?

Link intermediate filaments to the extracellular matrix (ECM) via integrins Signup and view all the answers

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

Epidermolysis Bullosa Signup and view all the answers

Which proteins are primarily associated with hemidesmosomes?

α6β4 integrins and plectin Signup and view all the answers

What is the primary role of focal adhesions?

Link actin filaments to the ECM via integrins Signup and view all the answers

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

Epithelial tissue Signup and view all the answers

Which component is NOT typically found in focal adhesions?

Keratin Signup and view all the answers

Electrical coupling is commonly associated with which type of muscle?

Cardiac muscle Signup and view all the answers

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

Rupturing of the basal epidermal layer Signup and view all the answers

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.