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Chapter 8

Chapter 8. Membrane Structure & Function. Membrane Structure, I. Shows Selective permeability Known as the plasma membrane Amphipathic - hydrophobic & hydrophilic regions Singer-Nicolson developed the fluid mosaic model. Membrane Structure, II. Phospholipids - membrane fluidity

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Chapter 8

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  1. Chapter 8 • Membrane Structure & Function

  2. Membrane Structure, I • Shows Selective permeability • Known as the plasma membrane • Amphipathic - hydrophobic & hydrophilic regions • Singer-Nicolson developed the fluid mosaic model

  3. Membrane Structure, II • Phospholipids - membrane fluidity • Cholesterol - membrane stabilization “Mosaic” Structure due to: • Integral proteins - transmembrane proteins • Peripheral proteins - surface of membrane • Membrane carbohydrates -~ cell to cell recognition; oligosaccharides (cell markers); glycolipids; glycoproteins

  4. Membrane Structure, III Membrane protein functions: • Transport • Enzymatic activity • Signal transduction • Intercellular joining • Cell-cell recognition • ECM attachment

  5. Membrane Traffic • Diffusion - tendency of any molecule to spread out into available space • Concentration gradient – moves from high to low • Passive transport - diffusion of a substance across a biological membrane • Osmosis - the diffusion of water across a selectively permeable membrane; DOWN the concentration gradient

  6. Water Balance • Osmoregulation - control of water balance • Hypertonic - higher concentration of solutes • Hypotonic - lower concentration of solutes • Isotonic - equal concentrations of solutes

  7. Water Balance Cells with Walls (plants, bacteria): • Require hypotonic external environments to keep their turgor pressure (water pressure pushing cell membrane out against cell wall) • Become limp or flaccid when lose turgor pressure • Plasmolysis - plasma membrane pulls away from cell wall

  8. Water Balance Cells without Walls (animals, most protist): • Require isotonic external environments • Hypotonic environments – cells swell & may burst with too much water pressure (Cytolysis) • May have contractile vacuoles (some protists) to control internal water pressure

  9. Specialized Transport • Transport proteins(with or without channels) • Facilitated diffusion - passage of molecules and ions with transport proteins across a membrane down the concentration gradient • Active transport - movement of a substance against its concentration gradient with the help of cellular energy

  10. Types of Active Transport • Sodium-potassium pump • Exocytosis - secretion of macromolecules by the fusion of vesicles with the plasma membrane • Endocytosis - import of macromolecules by forming new vesicles with the plasma membrane • Phagocytosis –cell “eating” • Pinocytosis – cell “drinking” • Receptor-mediated endocytosis (ligands)

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