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Questions and Answers
Epithelial tissue consists of closely bound cells forming sheets called ______.
epithelia
The surface of an epithelial cell that is exposed to the external environment is known as the ______ surface.
apical
A ______ junction is characterized by dense plaques of protein that join two epithelial cells.
desmosome
______ are transmembrane proteins that mediate cell–cell adhesion in animal tissues.
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An ______ junction attaches cells to one another or to the extracellular matrix.
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Cells may be linked by direct interactions or they may be held together within the extracellular ______.
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Mechanisms of cell cohesion govern the architecture of ______ and organs.
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Defects in the apparatus of cell junctions and the extracellular matrix underlie an enormous variety of ______.
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Attachments to other cells and to the extracellular matrix control the orientation and behavior of the cell’s ______.
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In connective tissue, the extracellular matrix is the main ______-bearing component.
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In epithelial tissue, the ______ of the cell is the main stress-bearing component.
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Cell–matrix junctions link connective tissue cells to the ______.
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The making and breaking of the attachments between cells and the modeling of the extracellular matrix govern the way cells ______ within the organism.
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Cell–matrix attachments bond epithelial tissue to the ___ tissue beneath it.
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In epithelial tissues, cells are tightly bound together into sheets called ___.
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The extracellular matrix consists mainly of a thin mat called the ___ lamina.
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Adherens junctions are connected to ___ filaments.
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Desmosomes are linked to ___ filaments.
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At the basal surface of epithelial cells, actin-linked cell–matrix junctions anchor actin filaments to the ___.
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Tight junctions occupy the most apical position, sealing the gap between the cells to prevent ___ from leaking across the epithelium.
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Gap junctions create passageways linking the ___ of adjacent cells.
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Proteins of the cadherin superfamily chiefly mediate attachment of cell to ___.
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Proteins of the integrin superfamily chiefly mediate attachment of cells to ___.
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Each type of cell junction depends on transmembrane adhesion proteins that span the ___ membrane.
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Desmosomes and adherens junctions link the cytoskeletons of ___ cells.
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The junctional complex is formed by the tight junction, adherens junction, and ___ junctions.
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Some integrins link to actin and form actin-linked cell–matrix ___.
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Study Notes
Cell-Cell Junctions
- Cells in multicellular organisms interact through direct cell-cell contact and the extracellular matrix.
- The extracellular matrix (ECM) is a complex network of proteins and polysaccharides secreted by cells.
- Cell adhesion is critical for maintaining the organization, function, and dynamics of multicellular structures.
Connective Tissue
- Connective tissue is composed of cells sparsely distributed within a matrix.
- The matrix in connective tissue bears most of the mechanical stress.
- Examples of connective tissue include bone, cartilage, and tendon.
Epithelial Tissue
- Epithelial tissue is characterized by tightly packed cells forming sheets called epithelia.
- Epithelia are found in the linings of organs and the outer coverings of the body.
- The ECM in epithelial tissue is a thin mat called the basal lamina.
- Epithelial cells are attached to each other through cell-cell junctions and to the basal lamina through cell-matrix junctions.
Types of Cell Junctions
- Adherens Junctions: Link actin filaments of adjacent cells, contributing to cell cohesion and tissue strength.
- Desmosomes: Link intermediate filaments of adjacent cells, providing strong adhesion and resisting stress.
- Tight Junctions: Seal the space between cells, preventing molecules from leaking across the epithelium.
- Gap Junctions: Create channels between the cytoplasms of adjacent cells, allowing direct communication and exchange of small molecules.
Transmembrane Adhesion Proteins
- Transmembrane adhesion proteins link the cytoskeleton to extracellular structures.
- Cadherins mediate cell-cell attachments, while integrins mediate cell-matrix attachments.
- Different subtypes of cadherins and integrins associate with specific cytoskeletal elements.
Anchoring Junctions (Table Style)
| Junction | Transmembrane Adhesion Protein | Extracellular Ligand | Intracellular Cytoskeletal Attachment | Intracellular Adaptor Proteins |
|---|---|---|---|---|
| Adherens Junction | Classical Cadherins | Classical Cadherin | Actin Filaments | α-Catenin, β-catenin, p120-catenin, vinculin |
| Desmosomes | Nonclassical Cadherins | Desmoglein/Desmocollin | Intermediate Filaments | Plakoglobin, plakophilin, desmoplakin |
| Actin-Linked Cell–Matrix Junction | Integrin | Extracellular Matrix Proteins | Actin Filaments | Talin, kindlin, vinculin, paxillin, focal adhesion kinase (FAK), numerous others |
| Hemidesmosomes | α6β4 Integrin | Extracellular Matrix Proteins | Intermediate Filaments | Plectin, BP230 |
The Extracellular Matrix (ECM)
- The ECM is a complex, often fibrous, network of proteins and polysaccharides.
- ECM components provide structural support, regulate cell behavior, and guide cell movement.
Cell-Matrix Junctions
- Integrin-mediated junctions link the cytoskeleton to the ECM.
- Actin-linked cell-matrix junctions anchor actin filaments to the matrix.
- Hemidesmosomes anchor intermediate filaments to the matrix.
The Plant Cell Wall
- The plant cell wall is a specialized ECM composed of cellulose microfibrils embedded in a matrix of polysaccharides and proteins.
- The cell wall provides structural support, regulates cell growth, and protects plant cells.
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Description
Explore the intricacies of cell-cell interactions and the significance of the extracellular matrix (ECM) in maintaining tissue structure. This quiz covers key concepts related to connective and epithelial tissues, focusing on their roles, characteristics, and functions in multicellular organisms.
