Cell Biology: Cell Junctions and Adhesions
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Questions and Answers

What is the primary function of focal adhesions?

  • Cell signaling
  • Migration and cell spreading (correct)
  • Protein synthesis
  • Cell division

Defective hemidesmosomes can lead to skin blistering diseases.

True (A)

What are the structural proteins that form gap junctions?

Connexins

Gap junctions allow the passing of _______ signals and sharing of small molecules.

<p>electrical</p> Signup and view all the answers

Match the functions of gap junctions with their descriptions:

<p>Passing of electrical signals = Allows communication between adjacent cells Sharing of small molecules and electrolytes = Helps maintain cellular homeostasis Protection from calcium damage = Prevents cell damage from high calcium concentration</p> Signup and view all the answers

Which of the following is NOT a protection mechanism provided by barriers?

<p>Control of nutrient absorption (A)</p> Signup and view all the answers

Barriers control the entry and exit of water and nutrients from the body.

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

What are the key components in a signaling pathway?

<p>Ligand, receptor, transducer, effector</p> Signup and view all the answers

The main function of tight junctions is to provide __________ between epithelial cells.

<p>barriers</p> Signup and view all the answers

Match the following components related to adhesion with their descriptions:

<p>Adhesion molecules = Connect cells together Plaque/linker proteins = Connect adhesion molecules to cytoskeleton Signalling molecules = Involved in cell communication and response Extracellular matrix (ECM) = Provides structural support to tissues</p> Signup and view all the answers

Which cytoskeletal element are tight junctions connected to?

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

Tight junctions primarily protect cells from high levels of radiation.

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

What is the primary function of tight junctions?

<p>Preventing leakage of molecules between cells (D)</p> Signup and view all the answers

Microbes can exploit tight junctions for their benefits.

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

Name one function of ZO proteins in tight junctions.

<p>Signal mediators</p> Signup and view all the answers

Anchoring junctions are common in tissues that experience high amounts of ___________ stress.

<p>mechanical</p> Signup and view all the answers

Match the junction type with its function:

<p>Tight junctions = Prevent leakage between cells Anchoring junctions = Strengthen cell membranes Desmosomes = Provide mechanical stability Gap junctions = Facilitate communication between cells</p> Signup and view all the answers

Which proteins are primarily associated with tight junctions?

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

Anchoring junctions play a minor role in tissues that are under mechanical stress.

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

What two major components make up anchoring junctions?

<p>Membrane-spanning structures and cytoskeletal elements</p> Signup and view all the answers

Tight junctions can be hijacked by ___________ for their own purposes.

<p>microbes/pathogens</p> Signup and view all the answers

Which of the following is a component of desmosomes?

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

Desmosomes primarily connect intermediate filaments from cell to cell.

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

Name one armadillo-like protein associated with desmosomes.

<p>Plakoglobin</p> Signup and view all the answers

Desmosomes help maintain _______ integrity in tissues.

<p>tissue</p> Signup and view all the answers

Match the following components with their respective roles in desmosomes:

<p>Desmogleins = Adhesion molecules Desmoplakin = Cytoplasmic anchoring Plakophillin = Intermediary signaling Plakoglobin = Structural support</p> Signup and view all the answers

What type of cytoskeletal element do desmosomes connect to?

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

Desmoyokin is a component found in certain muscle tissues.

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

What is the primary function of desmosomes?

<p>To maintain tissue integrity</p> Signup and view all the answers

Desmosomes recognize ligands on neighboring cells through _______ molecules.

<p>adhesion</p> Signup and view all the answers

Match the following molecules with their characteristics:

<p>Desmogleins = Cadherins involved in desmosome Desmoplakin = Plakin protein anchoring components Plectin = Cross-linker for intermediate filaments Desmocollins = Another type of desmosomal cadherin</p> Signup and view all the answers

What role does E-cadherin play in embryonic development?

<p>It helps in the formation of adherens junctions. (B)</p> Signup and view all the answers

E-cadherin can be exploited by pathogens for entry into cells.

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

What are some factors required to produce signals that polarize an epithelium?

<p>E-cadherin and other signaling factors.</p> Signup and view all the answers

Microbes can hijack E-cadherin to gain cell ______.

<p>entry</p> Signup and view all the answers

Match the following effects to their descriptions regarding E-cadherin:

<p>Cell entry = Microbes utilize E-cadherin as a receptor Toxin production = Disrupts E-cadherin structure Adherens junctions = Cellular structures maintained by E-cadherin Embryonic compaction = Starts at the 8-cell stage</p> Signup and view all the answers

At what developmental stage is E-cadherin first expressed in mouse embryos?

<p>8-cell stage (D)</p> Signup and view all the answers

E-cadherin plays no role in the structure of adherens junctions.

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

What type of cellular interactions are influenced by E-cadherin?

<p>Cadherin-mediated host-pathogen interactions.</p> Signup and view all the answers

Toxins produced by pathogens can disrupt the structure of ______.

<p>E-cadherin</p> Signup and view all the answers

What is one way that E-cadherin is crucial for epithelial cells?

<p>It is required for cell-cell adhesion. (C)</p> Signup and view all the answers

Flashcards

Barrier Function

Protection against chemicals, mechanical stress, bacteria, pathogens, and environmental factors like temperature/pH/radiation; control of water, nutrient entry/exit from the body.

Epithelia GI Tract

Tissue layers lining the gastrointestinal tract, with features for protection and controlled entry/exit of substances.

Signaling Pathway

A series of linked molecules including a ligand, initiating a response.

Adhesion Molecules

Proteins that allow cells to bind together.

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Tight Junctions (Occluding)

Adhesion junctions that seal the space between cells, preventing leaks and regulating passage of substances.

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Extracellular Matrix (ECM)

A surrounding substance providing support and structure to cells.

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Signal Pathway Components

Aligning Ligand-Receptor-Transducer-Effector for a cellular response, linked with adhesion molecules.

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Tight Junctions

Structures that link adjacent cells, forming a barrier to prevent leakage between them.

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Occludin

A protein component of tight junctions.

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Claudin

A protein component of tight junctions.

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ZO Proteins

Proteins that link tight junction proteins to the cytoskeleton.

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Anchoring Junctions

Specialized cell junctions that provide strong cell-to-cell connections.

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Cell Membranes

Thin layers that surround cells and regulate what enters and leaves.

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Cytoskeleton

A network of protein filaments that gives the cell its shape and helps with movement.

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Mechanical Stress

Physical forces acting on tissues or cells.

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Pathogens

Disease-causing organisms.

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E-cadherin expression

E-cadherin starts being expressed in a mouse embryo around the 8-cell stage

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Compaction in mouse embryos

An important stage in early mouse embryo development characterized by the cells getting tightly packed together.

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E-cadherin's role in epithelial polarization

E-cadherin is involved in signaling pathways that help determine the orientation and structure of an epithelial layer.

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Microbes hijacking E-cadherin

Some microbes use E-cadherin as a cellular entry point or disrupt E-cadherin's structure to affect adherens junctions.

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Adherens junctions

Structures in cells that are made up of E-cadherin helping cells stick together.

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Pathogen-cadherin interactions

Microbes and pathogens can interact with E-cadherin in multiple ways—through cell entry or by altering the structure of cadherin.

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Antibodies against E-cadherin

Antibodies that can be used to measure or analyze the amount or behavior of E-cadherin.

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Epithelial polarization

The process of cells becoming oriented in a tissue and creating different cellular domains in the tissue.

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Early mouse embryo development

The early stages of development in the mouse model, which include cell division and compaction.

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Experiment use in biological research

Using biological experiments to study and understand E-cadherin.

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Focal Adhesions

Specialized cell-cell junctions that are important for migration and cell spreading. They are dynamic structures involving adhesion molecules, cytoskeletal elements, and signaling proteins.

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Hemidesmosomes

Junctions that anchor epithelial cells to the underlying basement membrane, providing strong attachment and preventing cells from detaching.

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What do you think would happen to the skin if hemidesmosomes were defective?

Defective hemidesmosomes would lead to skin blistering diseases because the connection between the skin cells and the basement membrane would be weakened, making the skin prone to tear and separation.

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Gap Junctions

Channels between adjacent cells, formed by connexins, that allow the passage of small molecules and electrical signals, facilitating communication and coordination.

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What are the functions of gap junctions?

They allow for the sharing of small molecules and electrolytes, the passage of electrical signals, and protection from calcium damage by reducing the effects of concentration fluctuations.

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What are desmosomes?

Desmosomes are strong anchoring junctions that connect intermediate filaments from cell to cell, providing structural integrity to tissues.

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What are the key components of desmosomes?

Desmosomes are made up of desmosomal cadherins (desmoglein and desmocollin), plakins (desmoplakin and plectin), plakoglobin, and plakophillin.

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Desmoglein

Desmoglein is a transmembrane protein that belongs to the cadherin family and is a major component of desmosomes. It interacts with desmoglein on adjacent cells to form strong cell-cell adhesion.

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Desmoplakin

Desmoplakin is a large plaque protein found in the cytoplasm, interacting with both the desmosomal cadherins and the intermediate filaments. It helps anchor the desmosome to the cytoskeleton.

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What is the function of desmosomes?

Desmosomes are crucial for maintaining tissue integrity, especially in tissues subjected to mechanical stress, such as skin, heart muscle, and epithelial layers.

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What is the role of desmosomes in cell signaling?

Desmosomes can participate in cell signaling, influencing cell growth, differentiation, and even apoptosis. This occurs through interactions with other signaling pathways.

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What is the difference between desmosomes and adherens junctions?

Both desmosomes and adherens junctions are anchoring junctions, but desmosomes link intermediate filaments, while adherens junctions link actin filaments. They also differ in their specific cadherin components.

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What is the role of desmoyokin in desmosomes?

Desmoyokin is a protein specific to stratified epithelia, contributing to the strong adhesive properties of desmosomes in these tissues.

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How are desmosomes studied?

Desmosomes are studied using various techniques, including electron microscopy to visualize their structure, immunofluorescence to detect specific proteins, and genetic manipulation to understand their function.

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Study Notes

Course Information

  • Course Title: Biochemistry and Cell Biology
  • Course Code: BS31004
  • Date: October 16th, 2024
  • Instructor: Inke Näthke
  • Email: [email protected]
  • Textbooks: "Molecular Biology of the Cell" by Alberts et al. (various editions)

Learning Objectives

  • Understand different families of adhesion molecules and their structures, including other molecular components and their roles.
  • Understand the differences and similarities between different cell adhesions, including specific components, ligands, signaling principles, and cytoskeletal links.
  • Understand the specific functions of adhesion structures/junctions in tissues, especially epithelia.
  • Understand the experimental evidence that helped identify adhesion molecules, their interacting partners, and mechanisms that mediate their function.

Multicellularity Requirements

  • Requires strength and communication between cells within tissues to allow coordinated function of the entire organism as a whole.
  • Cell connections relay information (mediating signals) and transmit force (physical links) through cell junctions

Cell Signaling

  • All living cells sense and respond to their environment through mechanisms called cell signaling.
  • These mechanisms are part of a complex network governing basic cellular activities and coordinating cell actions.
  • Signaling types: (from environment to receiving cell): sending information via touching of the cell, via pushing or by secreting factors.
  • Environment sends 'signals'

Epithelia

  • Epithelia line the cavities of organs.
  • They comprise over 80% of human cancers.
  • Epithelia functions: protection against chemicals, mechanical stress, bacteria, environmental pathogens, temperature, pH, and radiation.
  • They control fluid and nutrient movement across tissues.

Epithelia along the GI Tract

  • Different types of epithelia (e.g., stratified squamous, simple columnar) have specific functions (e.g., protection, secretion, absorption) based on structure within different sections of the digestive system.

Tissue Layers

  • Epithelial tissue
  • Basal lamina
  • Connective Tissue
  • Collagen fibers

Lateral Membrane

  • Structure and function of cell-cell anchoring junctions, channel-forming junctions, and cell-matrix anchoring junctions.

Components of Signaling & Adhesion

  • Signaling Pathway Components: ligand/cue, receptor, transducer, effector
  • Adhesion Components: adhesion/extracellular matrix molecules, adhesion molecules, plaque/linker proteins, signaling molecules (e.g., kinases), cytoskeleton

Cell Junctions

  • Anchoring Junctions:
  • Actin filament attachments (adherens junctions).
  • Intermediate filament attachments (desmosomes).
  • Cell-matrix attachments(actin-linked cell-matrix adhesions, hemidesmosomes)
  • Occluding Junctions:
  • Tight junctions (vertebrates)
  • Septate junctions (invertebrates)
  • Channel Forming Junctions:
  • Gap junctions (animals)
  • Plasmodesmata (plants)

Desmosomes

  • Connect intermediate filaments between cells.
  • Components include desmosomal cadherins (desmogleins, desmocollins), desmoplakin, plakoglobin, and plakophilin.
  • Important in maintaining tissue integrity.
  • Desmosomes are composed: cadherin-family adhesion proteins, intermediate filaments, and dense plaque of anchor proteins.

Gap Junctions

  • Large protein family (connexins) form gap junctions in different tissues.
  • Six connexins form one connexon.
  • Mutations in connexins lead to diseases e.g. deafness.
  • Pass electrical signals and small molecules (electrolytes), reducing effects of concentration fluctuations.
  • Protect cells from calcium damage, closing during damage to neighboring cells.
  • Gap junctions are involved in signaling networks (e.g. involving p2r, aqp, ags8, rptpp, etc)

Focal Adhesions

  • Vital to cell development, especially in ectoderm, endoderm, and apoptotic cells, during attachment to the extracellular matrix (ECM) via specialized junctions.
  • Essential for cell migration and spreading.
  • Focal Adhesion Kinase (FAK) is important
  • Components: focal adhesion kinase, talin, vinculin,a-subunit of active integrins, beta- subunit of active integrins, actin filaments.

Hemidesmosomes

  • Crucial for normal skin function, connecting epithelial cells to the basal lamina.
  • Deficiencies lead to blistering skin diseases.
  • Composed of integrin (α6β4), type XVII collagen, laminin, and type IV collagen.

Additional notes (general summary)

  • Microbes/pathogens can hijack cadherins and tight junctions for their purposes.
  • Some pathogens disrupt E-cadherin structure affecting adherens junctions.
  • Signaling components of junctions differ between species.

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Adhesion in Epithelia BS31004 PDF

Description

This quiz covers the critical structures and functions of various cell junctions, including focal adhesions, gap junctions, and tight junctions. It also explores the role of cytoskeletal elements and signaling pathways in cell adhesion and barrier functions. Test your knowledge on the protection mechanisms provided by these junctions and how they interact with microbes.

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