1180-1202 The extracellular matrix of animal connective tissues

1180-1202 The extracellular matrix of animal connective tissues

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The extracellular matrix of animal connective tissues The extracellular Matrix is made and oriented by the cells within it o Macromolecules that make up the extracellular matrix are mainly made by cells in the matrix o Matrix macromolecules are secreted by cells called fibroblasts Glycosaminoglycan (GAG) chains occupy large amounts of space and form hydrated Gels o GAGs are unbranched polysaccharide chains composed of repeating disaccharide units o Polysaccharide chains are stiff and hydrophilic o Their high density of negative charges attracts cations like Na+ which cause a lot of water to be sucked into the matrix o This creates swelling pressure that enables matrix to withstand compressive forces Hyaluronan Acts as a Space filler and a facilitator of cell migration during tissue morphogenesis and repair o Hyaluronan is the simplest GAG o It has no sulfated sugars, all its disaccharide units are identical, chain length is enormous , and it is not generally linked covalently to any core protein o Hyaluronan is spun out directly from the cell surface by an enzyme complex , while other GAGs are made inside the cell and released by exocytosis o Hyaluronan is an important space filler during embryonic development o It can be used to force a change in the shape of a structure o In a developing heart, hyaluronan synthesis helps in this way to drive formation of the valves and septa that separate the heart’s chambers o When cell migration ends, the excess hyaluronan is generally degraded by the enzyme hyaluronidase o Hyaluronan is made in large quantities during wound healing Proteoglycans are composed of GAG chains covalently linked to a core protein o All GAGs are covalently attached to protein as proteogylcans
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o Membrane-bound ribosomes make the polypeptide chain or core protein of a proteoglycan o The polypeptide chain (core protein) is then threaded into the lumen of the endoplasmic reticulum o Polysaccharide chains are mainly assembled on this core protein in Golgi before dlivery to exterior of cell by exocytosis o Proteoglycans are distinguished from other glycoproteins by nature , quantity and arrangement of their sugar side chains o At least 1 of the sugar side chains of a proteoglycan must be a GAG o GAGs and proteoglycans associate with fibrous matrix proteins such as collagen and with protein meshworks such as the basal lamina, creating extremely complex composites Proteoglycans can regulate the activities of secreted proteins o Proteoglycans have an important role in chemical signaling between cells. o
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1180-1202 The extracellular matrix of animal connective tissues

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