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Questions and Answers

Cell - cell adhesion binds through ______.

CADHERINS

Cell-substrate adhesion binds through ______.

INTEGRINS

Adherens junctions are associated with ______ filaments.

actin

Desmosomes are attached to intermediate ______ filaments.

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

Focal adhesions are vital for development and involve attachment to the ______.

<p>extracellular matrix</p> Signup and view all the answers

Focal adhesion kinase is involved in signaling for cell ______.

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

Different integrins are used for different ______ and ECMs.

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

Inside-out signaling ultimately influences the binding of ______ to integrins.

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

The primary function of tight junctions is to provide ______ between epithelial cells.

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

Adhesion molecules play a crucial role in forming ______ junctions, which are crucial for cell communication.

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

The extracellular matrix (ECM) provides structural support and plays a role in ______ pathways.

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

In the context of cell adhesion, ______ proteins help connect the extracellular matrix to the cytoskeleton.

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

In cell signaling pathways, the ______ binds to the receptor to initiate a response.

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

Gap junctions close to prevent damage to other ______

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

Adhesion molecules recognize specific ______ on neighboring cells

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

Cells in tissues have specialized contact ______

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

Desmosomes are involved in more ______ signaling mechanisms

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

Cell adhesion mechanisms allow for stable and ______ communication

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

Adhesion does not only occur at classical cell ______

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

The extracellular matrix provides structural ______ to tissues

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

Cell signaling pathways are crucial for regulating ______ responses in tissues

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

In epithelial tissues, junctions like tight junctions provide a ______ barrier

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

Experimental methods in adhesion research often focus on ______ interactions

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

Desmosomes connect intermediate filaments from cell to cell using ______ cadherins.

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

Components of desmosomes include plakins like ______ and plectin.

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

Desmosomes contribute significantly to maintaining tissue ______.

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

Plakoglobin and plakophillin are classified as ______-like proteins.

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

In stratified epithelia, specific molecules such as desmoyokin are associated with ______.

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

The main function of desmosomes is to mediate adhesion ______ cells.

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

Cell signaling pathways can be influenced by the components of ______ junctions.

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

Desmosomes are connected to the cytoskeleton via intermediate ______.

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

Cell adhesion molecules recognize specific ______ on neighboring cells.

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

Experimental methods in adhesion research often involve studying ______ junctions.

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

What is the primary role of adhesion molecules in multicellularity?

<p>Providing strength and communication between cells (B)</p> Signup and view all the answers

Which of the following best describes the function of epithelial tissues?

<p>They line organs and cavities, and are significant in cancer development. (B)</p> Signup and view all the answers

How do cells typically communicate with each other within tissues?

<p>Through physical contacts and signaling molecules (C)</p> Signup and view all the answers

Which of the following statements about cell signaling is incorrect?

<p>Cell A can only signal Cell B through physical engagement. (C)</p> Signup and view all the answers

What factors may influence the signaling pathways in tissues?

<p>The specific adhesion molecules present (C)</p> Signup and view all the answers

What is the primary role of tight junctions in epithelial cells?

<p>Serving as diffusion barriers and confining transport proteins (A)</p> Signup and view all the answers

How does glucose enter the epithelial cells from the apical surface?

<p>By active transport mechanisms (C)</p> Signup and view all the answers

What mechanism prevents the backflow of glucose from the basal side of the epithelium?

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

What is the effect of tight junctions on transport proteins?

<p>They confine transport proteins to specific membrane domains (A)</p> Signup and view all the answers

In which part of the cell does glucose diffuse out after being actively transported in?

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

Which characteristic distinguishes tight junctions from other junctions?

<p>They act as diffusion barriers (D)</p> Signup and view all the answers

What would likely happen if tight junctions were compromised?

<p>Loss of barrier function, allowing unwanted substances to pass (A)</p> Signup and view all the answers

What structural role do anchoring junctions play in tissues exposed to mechanical stress?

<p>They strengthen cell membranes. (A)</p> Signup and view all the answers

Which proteins are primarily associated with tight junctions?

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

What can microbes and pathogens do in relation to tight junctions?

<p>Hijack them for their own purposes. (C)</p> Signup and view all the answers

Which of the following components is NOT a major part of anchoring junctions?

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

In anchoring junctions, how are cell membranes primarily reinforced?

<p>By strong membrane-spanning structures tethered to the cytoskeleton. (C)</p> Signup and view all the answers

What type of signaling pathway is influenced by anchoring junctions?

<p>Mechanical stress signaling pathways (B)</p> Signup and view all the answers

What is the key functional role of ZO proteins in tight junctions?

<p>To serve as signaling mediators (B)</p> Signup and view all the answers

Which of the following functions is NOT typically associated with tight junctions?

<p>Facilitating cell communication (A)</p> Signup and view all the answers

What is a consequence of the disruption of tight junctions by pathogens?

<p>Loss of epithelial barrier function (C)</p> Signup and view all the answers

What is the primary role of the intracellular tail of transmembrane adhesion proteins?

<p>To facilitate cell signaling by binding to specific proteins. (B)</p> Signup and view all the answers

Which of the following describes cadherins?

<p>Proteins that mediate cell-cell adhesion in a calcium-dependent manner. (A)</p> Signup and view all the answers

What type of binding do cadherins primarily exhibit?

<p>Homophilic binding with the same type of cadherin. (D)</p> Signup and view all the answers

How does the cytoplasmic tail of adhesion proteins contribute to cellular structure?

<p>By binding to the cytoskeleton and intracellular signaling proteins. (A)</p> Signup and view all the answers

What distinguishes different types of cadherins?

<p>The distinct sequences in their extracellular domains. (A)</p> Signup and view all the answers

What is the significance of the His-Ala-Val sequence in cadherins?

<p>It serves as a site for b-catenin attachment. (B)</p> Signup and view all the answers

Which of the following best describes the role of intracellular proteins in relation to adhesion proteins?

<p>They form a physical connection between adhesion proteins and the cytoskeleton. (C)</p> Signup and view all the answers

What distinguishes cadherins from other adhesion proteins?

<p>Their reliance on calcium for adhesion strength. (C)</p> Signup and view all the answers

Which role does b-catenin play in cadherin-mediated adhesion?

<p>It stabilizes the adhesion junctions by linking cadherins to the cytoskeleton. (A)</p> Signup and view all the answers

Flashcards

Anchoring Junctions

Cell-cell or cell-matrix junctions that connect cells to each other or to the extracellular matrix (ECM).

Cadherins

Proteins that mediate cell-cell adhesions.

Integrins

Proteins that mediate cell-matrix adhesions.

Adherens Junctions

Cell-cell junctions that are connected to actin filaments.

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Desmosomes

Cell-cell junctions that are connected intermediate filaments.

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Focal Contacts

Cell-matrix junctions that are connected to actin filaments. Dynamic.

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Hemidesmosomes

Cell-matrix junctions that are connected to intermediate filaments. Stable.

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Extracellular Matrix (ECM)

The material outside the cells, providing structural support and regulating cell behavior.

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Barrier Function

The ability of tissues to prevent the passage of substances, protect against harmful agents, and regulate the entry and exit of essential molecules.

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Epithelia in the GI Tract

Specialized tissues lining the gastrointestinal tract, providing protection, controlled entry and exit of substances, and contributing to digestion and absorption.

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Signaling Pathway

A chain of events that transmits information from the outside world to the inside of a cell, leading to specific responses.

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Adhesion Molecules

Proteins that mediate the attachment of cells to each other or to the Extracellular Matrix, forming cell junctions.

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Gap junctions

Specialized cell-to-cell connections that allow direct communication between cells.

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Directly communicating junction

A type of cell junction that allows direct communication between cells.

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Ligand

The part of a cell that adhesion molecules recognize on a neighboring cell, triggering communication.

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Cytoplasmic side of adhesion molecules

The part of the adhesion molecule that faces the cell's cytoplasm, associating with signaling molecules.

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Function of gap junctions

Enable stable/dynamic physical contact and communication (signals) between cells, acting as receptors and transmitting information (chemical, mechanical).

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Cell junctions

Specialized zones of contact between cells in tissues.

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Stable/dynamic contact

Cell junctions can shift and change their structure while maintaining stable communication.

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Non-junctional mechanisms

Mechanisms for cell-to-cell communication that do not occur at conventional cell junctions.

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Signaling networks

Complex systems for transmitting information between cells.

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Desmosomal Cadherins

Proteins that bind cells together in desmosomes. They are specifically desmogleins and desmocollins, ensuring strong cell-cell adhesion.

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Plakins

Proteins that link desmosomal cadherins to intermediate filaments inside the cell. Examples include desmoplakin and plectin.

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Plakoglobin and Plakophilin

Proteins that also play a role in connecting desmosomes to intermediate filaments, with similar function to plakins.

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What makes desmosomes unique from other junctions?

Desmosomes are characterized by being linked to the intermediate filament cytoskeleton, giving them a special role in resisting mechanical stress. Adherens junctions are linked to actin filaments, and tight junctions create a barrier.

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What are the critical roles of desmosomes in tissues?

Desmosomes play a crucial role in maintaining tissue integrity by holding cells together, especially in tissues subject to stretching or pulling forces. This helps to prevent tearing and maintain structure.

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How do we know desmosomes are important for tissue integrity?

Studies have shown that mutations in desmosomal proteins can lead to diseases like skin blistering and heart problems, demonstrating their importance in maintaining tissue structure and function.

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What is desmoyokin?

A protein specific to stratified epithelia, contributing to the unique structure and function of these tissues. It assists in maintaining tissue integrity and adhesion between layers.

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Signaling from Desmosomes

Desmosomes can initiate signaling pathways within cells that regulate cell behavior, growth, and differentiation. This communication contributes to tissue development and maintenance.

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How do desmosomes affect cell behavior?

Desmosomes can influence cell growth, differentiation, and migration by regulating the flow of information within cells. This is vital for proper tissue development and repair.

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What makes multicellularity possible?

Multicellularity requires strong tissues and communication between cells to function as a whole. This is achieved through cell junctions, which act as physical links and relay information between cells.

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What are the roles of cell junctions?

Cell junctions mediate signals between cells, providing physical links that transmit force. They are crucial for cell communication and tissue integrity.

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Types of cell signaling

Cell signaling can occur through physical contact (pushing, touching) or by secreting factors that trigger responses in receiving cells.

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Epithelia's role

Epithelia line organ cavities and produce >80% of human cancers. They act as a barrier, regulating the entry and exit of substances.

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What is the significance of cell adhesion?

Cell adhesion plays a crucial role in maintaining tissue strength and communication, allowing the entire organism to function as a whole. This is essential for both normal development and disease.

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Occluding Junctions

Tight junctions, also known as occluding junctions, act like a seal between cells, preventing fluid and molecules from passing through the space between them.

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Function of Tight Junctions

Tight junctions serve as diffusion barriers in epithelial tissues, regulating the passage of molecules and ions.

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Role of Tight Junctions in Glucose Transport

Tight junctions help maintain the directionality of glucose transport in the gut. They prevent backflow of glucose from the cell back into the gut lumen, ensuring efficient absorption.

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Apical vs. Basolateral Membrane

The apical membrane faces the lumen (open space) of an organ, while the basolateral membrane faces the underlying tissue or blood vessels.

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What is diffusion?

Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.

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Active Transport

Active transport is the movement of molecules across a membrane against their concentration gradient, requiring energy.

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How do tight junctions contribute to tissue integrity?

Tight junctions play a crucial role in maintaining tissue integrity by forming a barrier that prevents leakage and maintains the structural organization of the tissue.

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Tight Junction Plate

A complex protein structure that forms a barrier between cells, preventing the passage of substances between them. This barrier is essential for maintaining tissue integrity and regulating the flow of molecules.

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Occludin

A transmembrane protein that interacts with claudins to strengthen the tight junction barrier. It helps regulate the permeability of the tight junction and plays a role in cell signaling.

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ZO Proteins

A family of proteins that link the tight junction to the cytoskeleton. They help to maintain the structural integrity of the tight junction and play a role in signal transduction.

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Cingulin

A protein that interacts with ZO proteins and other tight junction components. It helps to regulate the organization and function of the tight junction.

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Rab3B/13 and Sec6/8

Proteins involved in transporting proteins and vesicles to the tight junction. They ensure the proper assembly and function of the tight junction.

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Hijacking Tight Junctions

Microbes and pathogens can exploit tight junctions for their own benefit, using them to gain access to the host cells and tissues.

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Mechanical Stress

Forces that act upon a tissue, such as stretching, compression, or tension. Anchoring junctions are especially important in tissues that experience high levels of mechanical stress.

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Adhesion protein

A transmembrane protein that connects cells to each other or to the extracellular matrix (ECM). It has an extracellular domain that binds to other cells or ECM, and an intracellular tail that binds to intracellular proteins.

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What is a cadherin?

A type of adhesion protein that mediates cell-cell adhesion. They are calcium-dependent and have a specific binding sequence. Some examples include classical, desmosomal, and protocadherins.

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What is an 'armadillo' repeat?

A specific protein structure found in b-catenin, a protein that interacts with cadherins. These repeats are important for cell signaling.

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What is an integrin?

A transmembrane protein that mediates cell-matrix adhesion. They have an extracellular domain that binds to ECM components and an intracellular tail that binds to the cytoskeleton.

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What is homophilic binding?

A type of interaction where adhesion proteins bind to identical proteins on neighboring cells.

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What is a desmosome?

A type of cell-cell junction that is connected to intermediate filaments. They are strong and help tissues resist mechanical stress.

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How do desmosomes contribute to tissue integrity?

Desmosomes hold cells together, forming a strong network that prevents tissues from tearing. This is crucial for tissues that are stretched or pulled on.

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What is the function of a gap junction?

Gap junctions are channels that allow direct communication between cells. They allow the passage of small molecules, ensuring rapid signaling and coordination between cells.

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Study Notes

Cell Adhesion and Cell Biology

  • Cells form tissues through cell adhesion
  • Multicellularity requires strength in tissues and communication between cells to coordinate
  • Cell-to-cell connections mediate signals and transmit force through cell junctions
  • Cell signaling mechanisms are complex processes that allow cells to respond to their environment

Learning Objectives

  • Students will be able to classify and differentiate various adhesion molecules.
  • Students will understand the differences and similarities in cell adhesion, including specific components, ligands, signaling principles, and cytoskeletal connections.
  • Students will be able to characterize the function of adhesion structures/junctions.
  • Students will be able to identify adhesion molecules, their interactions, and mediating mechanisms.

Epithelia

  • Epithelia line the cavities of organs and produce up to 80% of human cancers.
  • Epithelia act as barriers to protect the body from chemicals, mechanical stress, bacteria, environmental pathogens, and temperature/pH/radiation.
  • Epithelia control the entry and exit of water and nutrients.

Cell Signaling Pathway

  • Ligands/cues, receptors, transducers, and effectors are essential components of a signaling pathway.
  • Adhesion molecules, extracellular matrix molecules, plaque/linker proteins, and signaling molecules (e.g., kinases) participate in cell adhesion processes.

Junctions

  • Junctions are categorized into various types—anchoring, occluding, channel-forming, and signal-relaying.

Anchoring Junctions

  • Anchoring junctions include adherens junctions, desmosomes, and hemidesmosomes.
  • These junctions connect cells, linking to either the extracellular matrix or other partner adhesion proteins.
  • Adherens junctions connect cells via actin filaments— classical cadherins, non-classical cadherins.
  • Desmosomes utilize intermediate filaments and have desmosomal cadherins.
  • Hemidesmosomes anchor cells to the extracellular matrix via intermediate filaments and integrins.

Occluding Junctions (Tight Junctions)

  • Tight junctions form barriers, regulating the passage of small molecules and electrolytes.
  • Key proteins include claudins and occludins.
  • Tight junctions are responsible for preventing backward flow of glucose.

Gap Junctions

  • Gap junctions permit the passage of small molecules and electrolytes, allowing for direct electrical communication between cells.
  • Gap junctions are made up of connexins.
  • Calcium and pH regulate gap junction closure.
  • Gap junctions are essential for cellular signaling networks.

Hemidesmosomes

  • Hemidesmosomes connect cells to the extracellular matrix, essential for skin integrity.
  • Defective hemidesmosomes lead to skin blistering diseases.

Focal Adhesions

  • Focal adhesions are crucial for cell migration, cell spreading, and development.
  • Integrins serve as receptors, interacting with the extracellular matrix.
  • Focal adhesion kinase (FAK) plays a vital role in the dynamic assembly and disassembly of focal adhesions.

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