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Lecture 22

BIOL 3113 Lecture Notes - Lecture 22: Scleroprotein, Laminin, Proteoglycan


Department
BIOL
Course Code
BIOL 3113
Professor
Barbara S
Lecture
22

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22 Tissues
The cells of multicellular organisms are organized into cooperative assemblies of
different levels of complexity:
Tissues
assemblies of cells with similar functions
Organs
functional structures made of several tissues and cell types
Organ Systems
groupings of organs that work together to carry out higher order functions
Cells are held together in tissues at two levels:
Extracellular Matrix - produced and secreted by cells
provides the physical framework to which cells are attached
Cell Junctions - specialized regions of the cell membrane that are responsible for
attaching cells to: extracellular matrix and to each other
Extracellular Matrix
Extracellular material, produced by cells, provides structural framework for animal
tissues, organs and organisms
The ECM is produced primarily (but not exclusively) by connective tissue cells:
Fibroblasts ordinary connective tissue
Chondrocytes cartilage
Osteoblasts bone
Components:
*Glycosaminoglycans
*Proteoglycans
*Fibrous proteins
collagen - structural
elastin - structural
fibronectin - adhesive
laminin adhesive
Collagen
The most abundant protein in animals (up to 25% of the total proteins in mammals) and
the major component of the ECM
Structure

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Long, fibrous protein composed of three polypeptides (alpha chains) wrapped around one
another in triple-stranded helix
Physical properties
Flexible fibers
High tensile strength - resists extension
Can form flexible, woven networks that give support (mesentery)
Can form non-extensible bundles for transmitting mechanical work (tendons)
Synthesis and Assembly
Synthesized by fibroblasts, chondroblasts and osteoblasts
Secreted as procollagen molecules
Enzymatic cleavage in the extracellular space forms collagen molecules that self-
assemble into fibrils and fibers
Types of Collagen
Multiple collagen genes (21 in mammals) - produce different forms of collagen with
different molecular formulas, properties and functions
Structurally collagens fall into one of three groups:
*Fibril-Forming (Fibrillar) Collagens
*Fibril-Associated Collagens
*Network-Forming
Glycosaminoglycans (GAG's)
Structure of GAG's
Unbranched polysaccharide chains of repeating disaccharide subunits, composed of:
*Amino sugar
N-acetylglucosamine or N-acetylgalactosamine
may be sulfated (negatively charged)
* Sugar acid (uronic acid)
glucuronic acid (negative charge) or iduronic acid (negative charge)
Charge:
GAG's are highly negatively charged - polyanions
Four main types: hyaluronic acid, chondroitin sulfate and dermatan sulfate, heparan
sulfate and heparin, keratan sulfate
Functions of GAG's

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*Space-filling molecules
Inflexible chains occupy a large volume
Form "packing material" around cells, tissues and organs
*Bind water
High density of negative charges binds water more or less firmly, depending on
magnitude of density medium for diffusion of solutes through the tissues
*Produce hard, compression-resistant material (cartilage)
*Build gigantic protein-carbohydrate complexes
*Link cells into tissues
Proteoglycans
Structure
*Core protein - forms the backbone
*GAG's (approx. 80 sugars in length)
Variable size = up to 3 million daltons
Proteoglycan Aggregates
Natural form of most GAG's
Composition:
*Hyaluronan-forms the backbone
*Link protein
*Proteoglycans
Size
Several micrometers in length
MW - 100 million daltons or more
Proteoglycans - Functions:
Space filling molecules - "packing material"
*Form the hydrated ground substance of connective tissues
*Form intercellular gels of varying pore size - molecular sieves
*Provide an aqueous medium for the diffusion of small molecules
*Associate with fibrous proteins integration of tissue components
*Bind growth factors and other signaling molecules
slow release prolonged effect
binding inhibition
*Skeletal functions
bear weight (resist compression)
form attachments (resist stress)
Integrins
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