BIO130 Section Two Guide (5)

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Kenneth Yip

Cell Junctions, Cell Adhesion, and the Extracellular Matrix Cohesion is mandatory to form an organized multicellular structure o Governs the bodys shape, strength and the arrangement of its different cell types Junctions between cells create pathways for communication Attachment to other cells and to the ECM control the orientation of each cells internal structure o The making and breaking of these attachments and the modeling of the matrix governs the way cells move within the organism, guiding them as the body grows Defects within the cell junction, adhesion and ECM can lead to various diseases How can cells combine into millions and form a massive structure like a tree or horse? Two basic building strategies: o Depends on the strength of the ECM: Complex network of proteins and polysaccharide chains that cell secrete o Depends on the strength of the cytoskeleton inside the cells and on cell-cell adhesions: These adhesions tie the cytoskeletons of neighbouring cells together ECM in plants are important plant tissues owe their strength to the cell walls that surround each cell For animals, both structures are used for different purposes and different tissues Animal tissues fall into two categoriecs:nnectiveand epithelial o Connective : E.g., bone or tendon A lot of ECM cells are sparsely distributed within it The rich matrix is fibrous in polymers (especially collagen) and also bears the most of the mechanical stress to which the tissue is subjected Direct attachments from one cell to another cell is rare o Epithelial: E.g., lining of gut or the epidermal covering of the skin Cells are closely bound together into sheets caellp eidthelia ECM is scanty consists mainly ob fasil lamina Physical attachment is critical in both epithelial and non-epithelial tissues Junctions between cell and cell or between cells and matrix are diverse in structure and have four main functions: Junction Type Definition Classification Anchoring (including both cell-cell Actin filament attachment adhesions and cell-matrix sites: adhesions), transmit stresses1. cell-cell junctions and are tethered to (adherens junctions) cytoskeletal filaments inside 2.cell-matrix junctions the cell (actin-linked cell-matrix adhesions) Intermediate filament attachment sites: 1. cell-cell junctions (desmosomes) 2. cell-matrix junctions (hemidesomosomes) Occluding Seal the gaps between cells 1. tight junctions (in in epithelia so as to make vertebrates) the cell sheet into an 2.septate junctions (in impermeable (or selectively invertebrates) permeable) barrier Channel-forming Create passageways linking 1. gap junctions (animals) the cytoplasms of adjacent 2.plasmodesmata (in plants) cells Signal-relaying Allow signals to be relayed 1. chemical synapses
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