Chapter 5 - A CLOSER LOOK AT CELL MEMBRANES

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RESOURCES

  1. Textbook website:
    1. outline, quiz, and flash cards: select from resources for chapter 5.
  2. STARR and TAGGART 9th edition website:
    1. outline, quiz, and flash cards: select from resources for chapter 5.
  3. STARR AN TAGGART 10th edition website:
    1. outline, quiz, and flash cards: select from resources for chapter 5.
  4. On-Line Biology Book by M. J. Farabee 
    1. Introduction to the Cell Membrane
    2. Transport In and Out of Cells
  5. Kimball's Biology Pages
    1. Cell Membranes from Kimball's Biology Pages
    2. Facilitated Diffusion from Kimball's Biology Pages
    3. Active Transport from Kimball's Biology Pages
    4. Endocytosis from Kimball's Biology Pages
    5. Exocytosis from Kimball's Biology Pages
    6. Kinetics of Membrane Transport from Kimball's Biology Pages
    7. Cell Junctions from Kimball's Biology Pages
  6. The Biology Project  an interactive online resource for learning biology, developed at The University of Arizona
    1. Studying Cells 
  7. MIT Biology Hypertext Cell Biology
    1. Membrane Structure and Function
    2. Membrane Proteins 1.
    3. Membrane Proteins 2.
    4. Membrane Transport Mechanisms
  8. Cells Alive!  
  9. The Cell Membrane from Clarenville High's best Biology 2201 class
  10. ThinkQuest Interactive Tour of the Cell

Chapter Outline

4.0 -- It Isn't Easy Being Single

  1. A uniform and thin plasma membrane separates cell from external environment
    1. The plasma membrane regulates the exchange of materials and passage of molecules into and out of cells (between cytoplasm and surroundings.) e.g. salt and barnacles [fig. 5-1]
    2. permits homeostasis
    3. Receives information - permits cell to sense environmental changes and respond
    4. maintains structural and chemical relationships with neighboring cells
  2. Within the cytoplasm, exchanges are made across internal membranes of the organelles.

5.1 MEMBRANE STRUCTURE AND FUNCTION

  1. The Lipid Bilayer of Cell Membranes
    1. amphipathic molecules (fig 5-2) - phospholipids and cholesterol
      1. polar (hydrophilic) head
      2. two nonpolar (hydrophobic) tails
    2. self assembling, self sealing, impermeable to ions and polar molecules, EXCEPT H2O
  2. Fluid-mosaic Model of Membrane Structure: (Fig. 5-3)
    1. Lipid Component
      1. Phospholipids
      2. glycolipids
      3. cholesterol: in animal cells only;  fluidity buffer makes membrane more fluid at low T; stiffens phospholipids at high temperatures, makes membrane more impermeable to polar biological molecules. 
    2. Protein Component
  3. Overview of Membrane Proteins [Fig. 5.2]
    1. transport proteins
    2. receptor proteins
    3. recognition proteins
    4. adhesion proteins

5.2 Focus on Science: TESTING IDEAS ABOUT CELL MEMBRANES

 5.3 CROSSING SELECTIVELY PERMEABLE MEMBRANES

  1. selectively permeable [Fig. 5.7] - impermeable to some; facilitates others - permeable only to some material; regulates, helps maintain homeostasis
  2. diffusion [fig. 5.8]
    1. movement of material down a concentration gradient by kinetic energy (random movement)
    2. rate of diffusion is a function of size and shape of molecules, temperature, viscosity of medium; electric and pressure gradients can modify diffusion rate
    3. O2, CO2, H2O, numerous small molecules and ions diffuse in and out of cell
  3. Overview of Membrane Crossing Mechanisms [Fig. 5.9]

5.4 TRANSPORT BY PROTEIN CARRIERS [fig 5.10]

  1. Passive Transport (Facilitated Diffusion): (Fig. 5.11): 
    1. carrier proteins assist passage and accelerate movement of small solute molecules [e.g. glucose] through membrane that would be impeded by phospholipid bilayer.
  2. Active Transport: [fig. 5.12] 
    1. from lower to higher concentration; increases the gradient
    2. requires energy expenditure: ATP
  3. cotransport system

5.5 MOVEMENT OF WATER ACROSS MEMBRANES

  1. osmosis [fig. 5.13]
    1.  membrane permeable to water (solvent); impermeable to solute
    2. water diffuses from where it is more concentrated to less
  2. osmotic pressure
  3. tonicity: relative concentration of solutes
  4. isotonic (equal strength; rate in = rate out), hypotonic, hypertonic
  5. osmosis and tonicity [fig 5.14]
  6. turgor pressure
  7. contractile vacuole: removes excess H2O from fresh water protozoans
  8. bulk flow
    1. reverse osmosis; movement of water and solutes in the same direction against the concentration gradient in response to pressure (e.g. glomerular filtration)

5.5 BULK TRANSPORT ACROSS MEMBRANES

  1. Endocytosis and Exocytosis
    1. exocytosis [fig. 5.17a]: ejection of waste products; secretion of hormones
    2. endocytosis [fig 5.17b]
    3. phagocytosis "cell-eating" [fig. 5.19]: large solid material enclosed in vacuole
    4. pinocytosis "cell drinking": dissolved materials entrapped in small vesicles
    5. receptor mediated endocytosis [fig. 5.18]: brings in specific nutrients (ligands)
  2. cycling of membrane lipids and proteins [fig 5.20]

KEY TERMS FOR CHAPTER 5

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