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 EXTRACELLULAR FLUID Collagen Fibronectin Plasma membrane Micro- filaments CYTOPLASM Integrins Proteoglycan complex Polysaccharide molecule Carbo- hydrates Core protein Proteoglycan molecule Proteoglycan complex

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.