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Extracellular Matrix of the Animal Cell What is the extracellular matrix (ECM)? • Something that is made by virtually all multi-cellular organisms. • Elaborate covering outside animal cell membranes, occupying the space between cells. It is composed of: – Collagen, proteoglycans, and fibronectin, which the cell secretes. – Different from the plant extracellular matrix, which is composed of cellulose. • Many ECM components are involved in cell-to-cell interactions. Components of the ECM • Collagen – Most abundant glycoprotein (about half of the total protein in the body). – Forms strong fibers outside of the cell. • Fibers are embedded in a network made of proteoglycans. • Proteoglycans – Collagen fibers are embedded in a network made from proteoglycans. – Are another class of glycoproteins that consists of a small core protein with many carbohydrate chains covalently attached. – Large complexes can form when hundreds of proteoglycans become non-covalently attached to a single long polysaccharide molecule. Components (cont.) • Fibronectin – Glycoprotein that attaches the ECM to the cell itself. – Binds to cell surface receptors called integrins, which are built into the plasma membrane of the cell. • Integrins – Cell surface receptor that connects to fibronectin, which attaches to the ECM – Span the membrane and bind on their cytoplasmic side to associated proteins attached to microfilaments of the cytoskeleton. – Transmit’s changes between the ECM and the cytoskeleton – it integrates changes occurring outside and inside the cell. Fig. 6-30 Collagen Proteoglycan complex EXTRACELLULAR FLUID Polysaccharide molecule Carbohydrates Fibronectin Core protein Integrins Proteoglycan molecule Plasma membrane Proteoglycan complex Microfilaments CYTOPLASM ECM Effect on Behavior • By communicating with a cell through integrins, the ECM can regulate a cell’s behavior. • ECM can influence the activity of genes in the nucleus. – Speculated that information probably reaches the nucleus by a combination of chemical and mechanical signaling pathways. • Mechanical includes fibronectin, integrins, and microfilaments of the cytoskeleton. • The cytoskeleton may then trigger chemical signaling pathways inside the cell, leading to changes in the proteins being made by the cell and therefore in its function. • The ECM may help coordinate the behavior of all the cells within that tissue. – Direct connections (intercellular junctions) between cells also function in this coordination.