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Questions and Answers
What is the extracellular matrix (ECM)?
Any material produced by cells and secreted into the surrounding medium, usually applied to the non-cellular portion of animal tissue.
What are the roles of the ECM?
Mechanical strength, protection, and organization of cell behavior.
Which of the following macromolecules are included in the ECM?
Epithelial tissues have a low cell density with abundant extracellular matrix.
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What types of cells secrete the main components of the extracellular matrix in connective tissues?
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The matrix of bone and teeth is highly ______ to withstand compression.
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What are glycosaminoglycans (GAGs)?
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What type of ECM is blood plasma considered?
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GAGs play no role in the extracellular matrix.
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What is a key characteristic that differentiates connective tissues from epithelial tissues?
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Which of the following statements about the extracellular matrix is incorrect?
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How do the functions of the extracellular matrix influence cell behavior?
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What primarily determines the diversity of materials in the extracellular matrix?
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Which of the following is a function of the extracellular matrix?
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What is a primary reason for the transition from unicellular to multicellular organisms?
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How do some bacterial cells achieve initial attachment to surfaces?
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What defines a tissue in a multicellular organism?
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What challenge must multicellular organisms address beyond those faced by unicellular organisms?
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Which of the following best illustrates a function of the extracellular matrix (ECM)?
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What property of the ECM is essential for cells that undergo different roles in a tissue?
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Which statement best describes cell adhesion in multicellular organisms?
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What is a consequence of cells successfully adhering to one another in a tissue?
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What is the primary function of glycosaminoglycans (GAGs) in the extracellular matrix?
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Which type of GAG is characterized as being spun out from the cell membrane and not sulfated?
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What characteristic of the extracellular matrix in tendons contributes to its elasticity?
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Which macromolecules comprise the bulk of the extracellular matrix volume despite making up a smaller percentage of its mass?
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Which of the following GAGs is sulfated and derived from a specific disaccharide unit composed of D-glucuronic acid and N-acetyl-D-galactosamine?
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In which specialized extracellular matrix is the core structure determined by the presence of highly mineralized components?
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Which feature of blood plasma distinguishes it as a liquid form of the extracellular matrix?
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What distinguishes the chondroblasts' role in connective tissues from that of osteoblasts?
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What provides the extracellular matrix (ECM) with its characteristic elasticity?
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Which amino acids are particularly abundant in elastin?
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How do microfibrils and fibrillin contribute to elastin formation?
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What structural role does laminin play in the basal lamina?
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Which of the following is NOT a characteristic of fibrillin?
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Which statement about the basal lamina is accurate?
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What is the primary function of proteoglycans in the ECM?
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What is the composition of elastic fibers?
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What is the primary amino acid composition in collagen chains represented by GXY repeats?
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Which modification occurs to selected lysines during collagen synthesis?
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The stability of collagen fibrils is primarily enhanced by which process?
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What crucial vitamin is required for the hydroxylation of proline in collagen synthesis?
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What is the consequence of vitamin C deficiency in relation to collagen?
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Which type of collagen is most commonly found in skin, bones, and tendons?
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Collagen fibrils have a significantly longer lifespan compared to most enzymes. How long do collagen fibrils last?
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What is the role of hydrogen bonding in collagen structure?
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Study Notes
Cells to Tissue: ECM
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Cell adhesion is necessary for multicellular organisms.
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Unicellular organisms can exist alone.
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Bacteria can be either:
- Planktonic: free-floating in solution.
- Sessile: attached to surfaces, often within biofilms.
- Bacteria attach to surfaces using pili (fimbrae).
- Virulence factors: Help bacteria adhere and resist immune attack.
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Bacteria can be either:
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Multicellular organisms require mechanisms for:
- Cell-cell adhesion: Sticking cells together.
- Intercellular communication and transport.
- Specialized domains for different cell functions.
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Unicellular organisms can exist alone.
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Tissues are collections of similar cells and their extracellular matrix (ECM) with a defined function.
- Organs are formed from multiple tissues working together.
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Two main types of animal tissue:
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Connective tissues:
- Low cell density, abundant ECM.
- Examples: bones, tendons.
- ECM is load-bearing, providing mechanical support.
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Epithelial tissues:
- Tightly packed cells forming sheets.
- Thin ECM on one side – the basal lamina.
- Examples: gut lining, skin epidermis.
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Connective tissues:
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Extracellular Matrix (ECM):
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Definition: Material secreted and modified by cells into the surrounding medium.
- Animal tissues: Non-cellular portion of animal tissue.
- Plants and fungi: Also produce cell walls, but these are referred to as the ECM.
- Chitin and cellulose are the most abundant biopolymers on Earth.
- Diverse ECM compositions in different tissues allow for specialized functions.
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Functions of the ECM:
- Mechanical support: Provides tensile strength, compressive strength, and elasticity.
- Protection: Buffers against external changes and retains water.
- Organization: Controls cell behavior by binding growth factors and interacting with cell-surface receptors.
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Definition: Material secreted and modified by cells into the surrounding medium.
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Macromolecules of the ECM:
- Similar across tissues but vary in amounts and organization.
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Examples of specialized ECM:
- Bone and teeth: Highly mineralized for compression resistance.
- Cornea of the eye: Transparent for light transmission.
- Tendons: Highly elastic for force transmission.
- Blood plasma: Liquid form of ECM.
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Fibroblasts are the primary producers of ECM components in most connective tissues.
- Osteoblasts produce bone.
- Chondroblasts produce cartilage.
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Main macromolecular components of the ECM:
- Glycosaminoglycans (GAGs): Acidic polysaccharide derivatives, including proteoglycans.
- Fibrous proteins: Members of the collagen family.
- Non-collagen glycoproteins: Examples include fibronectin and laminin.
- Others: Elastin.
Glycosaminoglycans (GAGs)
- Unbranched polymers of repeating disaccharide derivatives.
- Contain amino sugars and sulfated acetylated derivatives of hexuronic acids.
- Interact with water, creating highly hydrated gels.
- Contributes to compressive strength and elasticity of ECM.
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Examples of GAGs:
- Hyaluronic acid
- Chondroitin sulfate
- Keratan sulfate
- Heparin sulfate
- Dermatan sulfate
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Proteoglycans:
- Core protein with multiple GAG chains attached.
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Function:
- Bind growth factors and cytokines.
- Regulate cell adhesion and migration.
- Form hydrated gels.
Fibrous proteins
- Provide tensile strength and structural support.
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Collagen:
- Most abundant protein in mammals.
- Forms triple helix structures.
- Type I Collagen: Found in skin, bone, tendons, and ligaments.
- Type IV Collagen: Forms the basal lamina.
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Elastin:
- Provides elasticity.
- Found in tissues that require stretching, such as skin, blood vessels, and lungs.
Non-collagen glycoproteins
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Fibronectin:
- Binds to collagen and integrins (cell surface receptors).
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Function:
- Cell adhesion
- Wound healing
- Embryonic development
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Laminin:
- Major component of the basal lamina.
- Binds to collagen, integrins, and other ECM components.
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Function:
- Provides structural support.
- Influences cell differentiation and migration.
Interactions within the ECM
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Cross-linking: Strengthen the ECM network.
- Occurs between different ECM molecules.
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Interactions with cells: Cells interact with the ECM through specific receptors.
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Integrins: Transmembrane proteins that bind to ECM molecules, including collagen, fibronectin, and laminin.
- Inside the cell: Integrins link to the cytoskeleton.
- Outside the cell Integrins bind to ECM molecules.
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Integrins: Transmembrane proteins that bind to ECM molecules, including collagen, fibronectin, and laminin.
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Function of these interactions:
- Cell adhesion: Anchoring cells to the ECM.
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Signal transduction: Communicating between the ECM and the cell.
- Changes in cell shape, motility, and gene expression.
ECM Remodeling
- Constant turnover and modification of the ECM.
- ECM is dynamic and responsive to cellular needs.
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Enzymes involved in remodeling:
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Matrix metalloproteinases (MMPs): Degrade ECM proteins.
- Role in development, wound healing, and disease.
- Hyaluronidases: Break down hyaluronic acid.
- Other enzymes are involved in adding, removing, and reorganizing molecules.
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Matrix metalloproteinases (MMPs): Degrade ECM proteins.
Importance of the ECM
- Essential for proper development and function of tissues.
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Role in health and disease:
- ECM defects: Contribute to tissue dysfunction and disease.
- Cancer: ECM changes can promote tumor growth and metastasis.
- Wound healing: The ECM is crucial for proper wound repair.
- Tissue engineering: The ECM is a key element in constructing artificial tissues and organs.
From Cells to Tissue: ECM
- Cells can exist alone (unicellular) or attached to surfaces, within a biofilm, or in multicellular organisms.
- Multicellular organisms face challenges regarding communication, transport, and specialized domain creation.
- Tissues are formed by similar cells and their ECM, carrying out specific functions.
- Organs are formed by multiple tissues working together.
- Animal tissues fall into two categories: connective tissues and epithelial tissues.
- Connective tissues have low cell density, abundant ECM, rare cell-cell contacts, and their ECM is load-bearing.
- Epithelial tissues have closely bound cells with thin ECM on one face (basal lamina).
Extracellular Matrix (ECM)
- ECM is any material produced by cells and secreted into the surrounding medium.
- Different tissues have specific ECMs, and the ECM is involved in tissue development, function, and disease.
- The ECM is a complex network of proteins and polysaccharides, modified outside the cell by enzymes.
- Functions of ECM include mechanical strength, protection, and organization of cell behavior.
- The ECM has diverse materials due to variations in the amounts and organization of its components.
Components of the ECM
- Fibroblasts secrete ECM components in most connective tissues.
- Osteoblasts form bone, and chondroblasts form cartilage.
- Main macromolecular components of the ECM:
- Glycosaminoglycans (GAGs)
- Fibrous Proteins (including collagen)
- Non-Collagen Glycoproteins (e.g., fibronectin, laminin)
- Others (e.g., elastin)
Glycosaminoglycans (GAGs)
- Unbranched polymers of repeated disaccharide derivatives, including amino sugars, sulfated acetylamino sugars, and uronic acids.
- Acidic and negatively charged, attracting positive ions and water, forming a gel.
- Contribute to 10% of ECM mass but 90% of volume.
- Provide compressive strength and are a metabolically cheap bulking agent.
Types of GAGs
- Hyaluronan is spun out from the cell membrane, is enormous (10^7 kDa), is not sulfated, and is not attached to proteins.
- Other GAGs include chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate, heparan sulfate, and heparin.
Collagen
- Chains consist of GXY repeats (Glycine-X-Y) where X is commonly proline and Y is commonly hydroxyproline.
- Hydrogen bonding between hydroxyproline groups stabilizes the triple helix.
- Lysines can be hydroxylated and glycosylated.
Collagen Synthesis
- Synthesis as pro-α-chain on RER.
- Assembly of procollagen.
- Procollagen is secreted into the extracellular space.
- Terminal propeptides are cleaved to form 100nm long collagen chains.
- Collagen molecules are crosslinked to form fibrils.
Scurvy
- A defect in collagen underlies scurvy.
- James Lind showed that citrus fruits prevented and cured scurvy.
- Vitamin C is required for hydroxylation of proline and lysine.
- In the absence of vitamin C, tissues containing collagen weaken.
Types of Collagen
- Type I is the most common fibrillar form, found in skin, bones, and tendons.
- Type II has similar tensile strength to cartilage.
- Type IX and XII don't form fibers and are fibril-associated, linking type I or II fibrils.
- Type IV and VII form a mesh structure in the basal lamina.
Elastin
- Provides the ECM with elasticity.
- Highly hydrophobic.
- Rich in proline and glycine.
- Non-glycosylated.
- Alternating stretches of hydrophobic residues and alanine/lysine-rich α helices.
- Crosslinking via α helical regions.
The Role of Fibrillin in Elastin Deposition
- Elastic fibers comprise an elastin core coated with a microfibril sheath.
- Microfibrils are made of glycoproteins, including fibrillin.
- Microfibrils act as a scaffold for elastin formation.
- Defects in the FIBRILLIN 1 gene result in Marfan syndrome (weak elastic tissue).
The Basal Lamina
- Plays important roles in structure, cell polarity, organization, and cell migration.
- Contains GAGs (heparan sulfate) and proteins (laminin, type IV collagen, nidogen, perlecan).
- Forms a barrier to certain cells and forms highways for cell migration.
Summary
- A tissue is a group of similar cells and ECM, performing a specific function.
- ECM is secreted by cells and has diverse compositions in different tissues.
- The basal lamina is a specialized ECM underlying epithelial cells, acting as a basement membrane
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Explore the concepts of cell adhesion and the formation of tissues from cells and their extracellular matrix (ECM). This quiz covers unicellular and multicellular organisms, the role of bacteria, and the characteristics of connective tissues. Test your knowledge on how cells interact and form specialized structures in organisms.
