Chapter 5 Membrane Structure & Function

1. Chapter 5 Membrane Structure & Function

2. Membrane structure, I Selective permeability Amphipathic polar & non-polar regions (ex. hydrophilic & hydrophobic) Davson-Danielli (1935-1970) protein “sandwich” Singer-Nicolson: “fluid mosaic” model currently widely accepted

3. Membrane structure, II Phospholipids membrane fluidity Cholesterol fluidity/stabilization “Mosaic” Structure Integral proteins trans-membrane proteins Peripheral proteins surface of membrane Membrane carbohydrates cell to cell recognition; Oligosaccharides (cell markers); glycolipids glycoproteins

4. Membrane structure, III Membrane protein function: •transport •enzymatic activity •signal transduction •intercellular joining •cell-cell recognition •ECM attachment

5. Membrane traffic Diffusion movement of a substance from an area of high concentration of that substance to an area of low concentration of that substance. Concentration gradient imbalance in concentration Passive transport diffusion of a substance across a biological membrane without the need for energy Osmosis the diffusion of water from an are of high concentration of water to an are of low concentration of water across a selectively permeable membrane

6. High Concentration Active-Need ATP (against (or with) gradient) Active Transport Passive (with gradient) Diffusion, Osmosis, Facilitated Diffusion Low Concentration

7. Water balance Osmoregulationcontrol of water balance Hypertonichigher concentration of solutes Hypotoniclower concentration of solutes Isotonicequal concentrations of solutes Cells with Walls: Turgid (very firm) Flaccid (limp) Plasmolysis plasma membrane pulls away from cell wall

8. Specialized Transport Transport proteins 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

9. Types of Active Transport Sodium-potassium pump Exocytosissecretion of macromolecules by the fusion of vesicles with the plasma membrane Endocytosisimport of macromolecules by forming new vesicles with the plasma membrane •phagocytosis •pinocytosis •receptor-mediated endocytosis (ligands)