L02 cell membrane_


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L02 cell membrane_

  1. 1. Membrane structure and mechanisms of cell adhesion and locomotion
  2. 2.  Separate the cell interior from an external environment  Take part in cell functions  Partition the c y toplasm into compartments - organelles  Mediate contacts with other cells or surrounding environment  Create a semipermeable barrier – impermeable for macromolecules and selectively permeable for ions Biomembranes
  3. 3. Biomembr anes <ul><li>Development of membrane concept </li></ul><ul><li>1890 : cell surface is of lipidic nature (Overton) </li></ul><ul><li>1926 : cellular membranes consist of lipid bilayers (Gorder and Grendel) </li></ul><ul><li>1943: the surface of lipid bilayer is coated by proteins (Davson and Danielli) </li></ul><ul><li>1960: unit membrane (Robertson) </li></ul><ul><li>1972: fluid mosaic model (Singer a Nicholson) </li></ul><ul><li>1980: detailed structure of membrane proteins (Unwin a Henderson) </li></ul>
  4. 4. Chemical composition of membranes membrane lipids phospholipids, sfingolipids , sterols membrane proteins (glycoproteins) Phospholipids: ( phosphoglycerides ) phosphatidyl- cholin ethanolamine serine inositol Sphingolipids -sfingosin Sterols cholesterol ergosterol
  5. 5. Physical features of biomembranes <ul><li>Stabili ty of the bila y er : </li></ul><ul><li> facilitated by hydrophobic interaction between fatty acid chains </li></ul><ul><li> unsaturated fatty acids decrease the bilayer stability </li></ul><ul><li> Sterols increase the bilayer stability </li></ul><ul><li>Polarity of phospholipids </li></ul><ul><li>hydrophilic ends (PO 4 , , </li></ul><ul><li>COOH, OH, NH 3 </li></ul><ul><li>hydrophobic ends </li></ul><ul><li>fatty acid chains </li></ul><ul><li>Self-assembly into bilayers liposomes , myeline </li></ul><ul><li>structures </li></ul><ul><li>Lipid asymmetry </li></ul><ul><li>Membrane fluidity </li></ul>
  6. 6. Mobility of membrane phospholipids Membrane fluidity rotation lateral migration flip-flop – transversal diffusion transition point
  7. 7. Heterogeneity of membrane lipids and their asymmetric distribution in bilayer. Rafts: small islands of sphingolipids and cholesterol creating a separate phase (50 nm in diameter) in outer leaflet of plasma membrane
  8. 8. Membrane proteins - enzymes - receptor proteins - transport proteins (pumps,carriers, channels) - linkers Association of membrane proteins with the lipid bilayer
  9. 9. Membrane proteins: - have both hydrophobic and hydrophilic regions - the hydrophobic region extend through the bilayer and is formed by hydrophobic amino acids hydrophilic regios are exposed to the aqueous environment on either side of the membrane - Peripheral proteins are attached to the bilayer by lipid groups (dolichol)
  10. 10. Human red cells in scanning elektron microscope
  11. 11. Membrane skeleton network of proteins under the plasma membrane. In red cells the membrane skeleton is formed by spectrin, actin filaments and attachment proteins
  12. 12. Glycocalyx: a coat of poly- a oligosaccharides on the surface of plasma membrane
  13. 13. Extracelullar matrix (ECM): <ul><li>Complex network of polysaccharides and proteins produced by cells of connective tissue (fibroblasts, chondrocytes, osteocytes etc.) Main components: </li></ul><ul><li>collagens, elastin – structural proteins </li></ul><ul><li>fibronectins – fibrous adhesive proteins interconnecting ECM to a </li></ul><ul><li>and laminin s meshwork </li></ul><ul><li>proteoglycans – gly c oproteins forming a gel </li></ul><ul><li>ECM calcified in bone and teeth </li></ul><ul><li>Ropelike in tendon </li></ul><ul><li>Transparent in cornea </li></ul><ul><li>Plant cell wall – specific type of extracellular matrix </li></ul>
  14. 14. Cellular interactions and cell adhesion carry out a structural role, important in cell migration, growth, immunological function, cell recognition, tissue repair, differentiation and embryogenesis
  15. 15. Cell-to-cell interaction: C ell adhesion molecules ( CAM ): cadherin, Ig superfamily CAM, mucin-like CAM, integrins selectins
  16. 16. Basal lamina <ul><li>T hin tough sheet of extracellular matrix . Composition : collagen t y pe IV tensile strength </li></ul><ul><li>laminin provides adhesive sites for integri n molecules in the plasma membrane of epithelial cells other proteins </li></ul>
  17. 17. Structure and function of basal lamina
  18. 18. Keratinocyte crawling over surface
  19. 19. Model of focal adhesion Components: ECM Integrin Vinculin Talin Actin filaments
  20. 20. Plasmamembr ane a nd cell migration <ul><li>Cell crawling – formation of filopodia (thin stiff protrusions) and lamelipodia (thin sheet-like extensions) – due to actin polymerization. The new position of the plasma membrane is fixed by focal adhesion complexes </li></ul><ul><li>Contraction of a part of the cytoplasm, invagination of the plasma membrane or invagination of cell layers due to the activity of actin-myosin I or actin-myosin II complexes: actin filaments are anchored to the plasma membrane. Actin filaments slide over each other, the sliding is mediated by myosin motors. </li></ul>
  21. 21. Key terms <ul><li>1. Biomembranes – overview of the structure and functions </li></ul><ul><li>2. Development of membrane concept: lipid layer, lipid bilayer, phospholid bilayer, localization of membrane proteins </li></ul><ul><li>3. Structure of the phospholipid bilayer </li></ul><ul><li>4. Hydrophilic head and hydrophobic tails. Self-assembly of the bilayer. Lipid asymmetry. Membrane rafts. Liposomes. </li></ul><ul><li>5. Model of the fluid mosaic. I ntegr al a peripheral proteins. </li></ul><ul><li>6. Hydrophobic regions of integral proteins </li></ul><ul><li>7. Membrane glycoproteins </li></ul><ul><li>8. Glycocalyx </li></ul><ul><li>9. Extracelular matrix: main components: collagen, elastin, fibronectin, laminin, proteoglycans </li></ul>
  22. 22. Key terms – cont. <ul><li>10. Basal lamina: components and function </li></ul><ul><li>12. Plasmamembrane and cell migration: cell crawling and contractile movements </li></ul><ul><li>13. Focal adhesion </li></ul>