extracellular proteins receptors - 12

extracellular proteins receptors - 12 - 121 (Biol.Chem.410A...

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12-1 Cell and Molecular Biology (Biol. Chem. 410A) Lecture #12 Harry R. Matthews, Ph.D. October 11, 1996 Extracellular Proteins; Receptors Clinical correlations:  scurvy  osteogenesis imperfecta Ehlers-Danlos syndrome  erbB proto-oncogene Learning objectives:  Cell junctions  The extracellular matrix  Collagen  Extracellular signaling molecules  Receptors Optional reading: Stryer IV: Chapter  11 xtracellular 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. E Cell junctions Chemically, 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 
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