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BIOLOGY 2B03 (285)
Kim Dej (39)
Lecture 8

CELL BIO 2B03 lecture 8.docx

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Kim Dej

CELL BIO 2B03 Cell Adhesion: Stable Interactions  Essential for evolution of multicellular organisms because the interactions allow specialized cells to attach and to recognize one another allowing for tissues to form and perform a specific task  Important for embryogenesis: o All our cells are proliferating and dividing and differentiating so that like cells recognize one another and contact each other  Molecules involved in any cell adhesion action are called CAMs (Cell Adhesion Molecules); allow cells to segregate into distinct tissues o Cadherins o Ig family o Integrins o Selectins  After aggregation, cells form specialized cell junctions; o These stabilize cell-cell interactions o Promote communication between adjacent cells  Tight Junctions: o Freeze-fracture technique o An array of proteins o No gap/space where something can diffuse through; the two membranes are tightly apposed to one another o Surface between the two cells with no rooms for movement between the two cells  Gap Junctions: o Occurs just below the tight junction o Allows channels to form between the neighboring cells o One channel composed of hemi-channel (a complex of proteins that passes through the membrane of each of the cells) o Allows small molecules to leave the cell (approx. 2 nm in diameter)  Ions  cAMP  fluoresoein JUNCTIONS FACILITATE STABLE ASSOCIATION BETWEEN CELLS AND ALLOW COMMUNICATION BETWEEN CELLS Extravasation: Adhesive interactions and motile cells:  Endothelial cells (specialized epithelial cell) form the inner lining of the blood vessels o Leukocytes respond to infection o Leukocytes must move out of the blood vessel into damaged or infected tissue = extravasation o Movement of leukocytes into tissues depends upon a precise sequence  Leukocytes: 1. Granulocytes: contain toxins for killing pathogens a. Neutrophil, eosinophil, basophil granulocytes 2. Monocytes (macrophages): phagocytosis 3. Lymphocytes a. NK cells – lysis of virally infected cells and tumor cells b. T and B cells – immune response (undergo extravasation) Overview of extravasation process: 5 Steps 1. Leukocytes are captured: there is transient association with the endothelial wall  Attraction/chemotaxis: mediated through cytokines of endothelial cells that make up the blood vessel wall o At site of infection, macrophages respond first recognizing a bacterial infection – recognize from the outside of the blood vessel (they produce the chemical signal, called the cytokine) o The signal is received by a receptor on the endothelial cell o P-selectins (cell adhesion model) are membrane anchored proteins that recognize modified glycoproteins, forming an interaction between the two cells  P-selectins are produced in the ER, transported through the Golgi and reside in secretory vesicles, upon receiving cytokine signal the s
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