EXTRACELLULAR MATRIX - COMMON FEATURES I. Material deposited outside plasmalemma in between cells II. Primary function is support A. Animals tough elastic structures of tendons, cartilage, and bone B. Plants, algae, fungi, and prokaryotes -> "cell wall" III. Many other diverse secondary functions dependent of pattern and type of materials A. Cell communication & regulation in Animals 1. Cell division, adhesion, motility, migration, and differentiation in embryogensis 2. Large molecular filters in capillaries and kidney glomeruli 3. Reaction to wounding and disease B. Fungi, algae, and prokaryotes 1. Determines cell shape 2. Protection against osmotic lysis, UV radiation (melanin), lytic enzymes of other organisms 3. Large molecular filters between external environment and cytoplasm 4. Binding sites for certain enzymes involved in feeding and attachment C. Plants 1. Determines cell shape 2. Cell to cell communication 3. Protection from mechanical damage and disease organisms 4. Recognition and binding of external molecules 5. Control of water pathways (lignin) IV. Extracellular matrix of all eukaryotes share two common structural elements A. Fibers 1. Long, semicrystalline elements 2. Provide resistance to stretching and other tensile forces B. Network 1. More or less elastic, interlocked assembly of branched molecules 2. Hold fibers in place 3. Provide resistance to compressive forces via trapping and retarding flow of water molecules V. Physical properties of extracellular matrices determined by A. Kinds of fiber and network molecules present B. Degree of crosslinking of fibers via network molecules C. Amount of trapped water D. Types of additional material within the matrix 1. Calcium phosphate crystals in bone 2. Lignin in plant cell walls ANIMAL EXTRACELLULAR MATRIX I. Fiber A. 16 different types of Collagens B. Insoluble glycoproteins with high content of glycine and two modified amino acids (hydroxylysine & hydroxyproline) + carbohydrate (glucose & galactose) C. Three alpha-helical polypeptide chains terminated by caplike, globular segment D. Procollagen synthesized in ER, moved through Golgi complex into secretion vesicles, which fuse with plasmalemna, dumping procollagen to extracellular matrix area E. Enzymes in matrix area convert procollagen to collagen II. Network A. Highly diversified group of glycoproteins, "proteoglycans" B. Linear polypeptide core with side-linked long carbohydrate chains IV. Interlinking Molecules A. Large, complex group of molecules with multiple binding sites cross-link collagen and proteoglycan molecules together FUNGAL EXTRACELLULAR MATRIX I. Primarily studied by Enzymatic Dissection and Electron Microscopy (Hunsley and Burnett, 1970) II. Fiber A. Varies between Phyla B. Chitin = long, straight chains of B-1,4-linked N-acetylglucosamine 1. Also in insects, crustaceans, and other arthropods C. Chitosan = poorly acetylated or non-acetylated form of chitin D. Glucans = branched polymers of glucose E. Cellulose III. Network A. Glucans B. Various glycoproteins IV. Cell wall consists of different zones A. From tip to base in growing hyphae B. From Plasmalemma (youngest) to outside (oldest) in mature hyphae 1. Chitin + Protein 2. Protein Layer 3. Glycoproteins + Protein 4. Glucans IV. Components can change substantially at different stages of life cycle PLANT EXTRACELLULAR MATRIX I. Fiber A. Cellulose = long straight chains of B1,4-linked glucose 1. 20 - 50% dry weight 2. 15% volume B. Form Micofibrils with quasi-crystalline structure (10-85 nm diameter) via hydrogen bonding between cellulose molecules C. Callose = long chains of B1,3-linked glucose 1. Sieve tube elements and wounded plant cells II. Network A. Hemicellulose = branched chains of glucose + other sugars 1. 20% dry weight 2. Form sheathing layers around microfibrils via hydrogen bonds 3. May be neutral or acidic in pH range of cell wall B. Pectins = branched chains of polysaccharides with galacturonic acid or galacturonic acid + rhamnose backbones 1. 25 - 30% dry weight 2. Form stable gels of various viscousity via water trapping 3. Highly acidic in pH range of cell walls = electrostatic bonds with other molecules (Interactions with Ca+2 might play a linkage role?) III. Other network components A. Various enzymes 1. Transferases involved in moving sugar groups from precusers to network components 2. Hydrolytic enzymes that remove sugar groups and create binding sites in network components 3. Peroxidases, phosphatases, proteases, oxidases, and reductases a. Some of these hydrolyze molecules of cell walls of invading fungi and bacteria B. Structural Glycoproteins rich in hydroxyproline or glycine 1. Extensins confer rigidity to cell wall via ionic attractions with negatively charged network components and covalent bonds with other extensins and pectins C. Lectins 1. Soluble glycoproteins with multiple binding sites to cross link carbohydrate groups of other network components 2. Can bind with chitins of invading fungi 3. Part of recognition mechanism between root hairs and Rhizobium bacteria in legume roots D. Silica important component of cell walls of grasses and Equisitum E. Lignin 1. Dense, insoluble substance formed by complex alcohols covalently linked into branched network 2. Lignification makes cell walls hydrophobic which is important in function of endodermis of monocot roots and vascular cells F. Suberin, Cutin, and Waxes 1. Insoluble substances formed by complex fatty acids covalently linked polymers 2. These substances make cell walls hydrophobic which is important in function of endodermis of dicot roots, epidermal cells, and periderm (bark) cells IV. Structure of cell wall only partially understood through enzymatic digestion studies A. Cellulose microfibrils surrounded by hydrogen-bonded hemicellulose sheath B. These units cross-linked via hydrogen-bonded pectins C. Cross-linkage may be reinforced via extensins and other glycoproteins D. This network is open enough to admit water, ions, and small molecules but has great resistance to stretching and compression E. Size and orientation of cellulose microfibrils varies between 1. First formed primary cell wall 2. Latter formed secondary cell wall F. Proportions of cellulose, hemicellulose, and pectins varies between 1. Layers within the cell wall 2. Different types of cells 3. Different species of plants V. Synthesis of cellulose microfibrils occurs at the plasmalemma A. Linear or circular groups of protein size particles embedded in grooves in the membrane thought to synthesize cellulose microfibrils from glucose B. Microtubules thought to somehow be involved in the orientation of microfibrils VI. Synthesis of network molecules A. Initial precursors via Golgi apparatus -> vesicles to plasmalemma B. Final synthesis and linkages via enzymes in extracellular matrix COMMUNICATION BETWEEN CELLS ANIMAL CELL JUNCTIONS I. Adhesive junctions A. Hold cells together in fixed positions in tissues II. Tight junctions A. Prevent diffusion from occuring through extracellular space between cells III. Gap junctions A. Open channels between plasmalemma of adjacent cells that permit flow of ions and small molecules between them B. Consist of circular groups of 4 of 6 connexin protein units called a connexon C. Molecules up to 1200 daltons can pass through D. Channels are regulated via Ca+2 and H+ 1. Low Ca+2 -> open channels 2. Higher Ca+2 _or H+ -> channels narrow FUNGAL SEPTA OR CROSS WALLS IN HYPHAE I. Pseudosepta (Zoosporic fungi) A. Sievelike cross walls perforated with many pores II. Majority of fungi have Simple Septa A. Cell wall gradually taper to a central pore 0.05 - 0.5 in diameter B. 3-4 Woronin bodies in cytoplasm adjacent to pore 1. Membrane bound crystalline collection of protein, phosphorus, and sulfer 2. Woronin bodies block pores if cell becomes damaged or aged III. Dolipore Septum occurs in mushrooms A. Central pore surrounded by doughnet like ring of cell wall material B. Pore is capped with endoplasmic reticulum cap which is either continuous or with one of more pores C. Cytoplasm, organelles can pass through the cap and pore PLANT CELLS I. Via Plasmadesmata in primary cell wall A. Plasmalemma continuous between adjacent cells B. Endoplasmic reticulum between adjacent cells connected via central tubule C. Upper limit of free movement = 700 daltons D. Antibodies against connexin proteins react with plasmatesmata E. Evidence that movement regulated by divalent cations II. Via Pits in secondary cell wall A. Regions where secondary cell wall is not deposited B. Two continuous regions which can vary independently in shape and size 1. Pit canal = adjacent to cell lumen or plasmalemma 2. Pit chamber = adjacent to primary cell wall 3. Different cell types have different types of pits C. Pit pairs are formed via alignment of pits of two adjacent cells