extracellular proteins receptors - 12

extracellular proteins receptors - 12 - 12-1Cell and...

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Unformatted text preview: 12-1Cell and Molecular Biology (Biol. Chem. 410A)Lecture #12Harry R. Matthews, Ph.D.October 11, 1996Extracellular Proteins; ReceptorsClinical correlations:• scurvy osteogenesis imperfecta•Ehlers-Danlos syndrome• erbB proto-oncogeneLearning objectives:• Cell junctions• The extracellular matrix• Collagen• Extracellular signaling molecules• ReceptorsOptional reading:•Stryer IV: Chapter 11xtracellular proteins may be fixed in their location in tissues and may provide the extracellular environment—extracellular matrix— for the cells of the tissue. Extracellular proteins may also medi-ate cell-cell interactions within tissues and between neighboring tissues. Other extracel-lular proteins, such as peptide hormones, may move through the body and interact with cells of distant tissues.ECell junctionsChemically, the most intimate form of cell–cell contact is the gap junction. In this structure, a channel is formed linking the cytoplasms of the two cells. The proteins of the channel reg-ulate the flow of small molecules and ions between the two cells. The channel proteins keep the plasma membranes apart, hence the name gap junction.Cell–cell contacts are made at intercellular junctions. Direct contacts between the plasma membranes of adjacent cells, particularly in epithelial tissues, are called tight junctions. A tight junction prevents the passage of extra-cellular molecules and, to a varying extent, ions between the cells and even restricts the diffusion of transmembrane components with-in their own plasma membrane, polarizing the cells so that different membrane functions such as specific receptors, expressed on one side or another of the epithelium, are restric-ted to diffuse within their own section of the plasma membrane. Anchoring junctions may link cellular cyto-skeleton proteins through the plasma mem-brane to the extracellular matrix or an adja-cent cell. Such an anchoring junction involves a transmembrane protein that binds the cyto-skeleton on the cytoplasmic face of the plasma membrane. On the extracellular face of the plasma membrane, the anchoring junction binds either the extra-cellular matrix (focal contacts, adhesion plaques or hemidesmo-somes) or a receptor on another cell (adhesion belt or desmosomes). Extracellular matrix proteins.Many of the extracellular materials are fila-ments made from fibrous proteins, mainly col-lagen and elastin, and adhesion proteins such as fibronectin and laminin. Collagens form a family of proteins with a tissue–specific distri-bution, including types I, II and III—found in connective tissue such as filaments—and types IV and V found in basal laminae—form-...
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