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In other words, the extracellular matrix largely determines how a tissue looks and functions. The extracellular matrix is made up of proteoglycans, water, minerals, and fibrous proteins. A proteoglycan is composed of a protein core surrounded by long chains of starch-like molecules called glycosaminoglycans.
The main ingredients of the extracellular matrix are glycoproteins secreted by the cells. (Recall that glycoproteins are proteins with covalently bound carbohydrates, usually short chains of sugars.) The most abundant glycoprotein in the ECM of most animal cells is collagen, which forms strong fibers outside the cells.