IB SL Biology: Membranes

Fluid Mosaic Model
1. Phospholipid bilayer
  1. Phospholipid molecules
    1. Hydrophobic hydrocarbon tail
      1. Attracted to each other; on inside of membrane
    2. Hydrophilic hydrocarbon head
      1. Attracted to water; on outsides of membrane
  2. Very stable
  3. Fluid
    1. Allows change of shape
      1. Allows vesicles to be pinched off
        Allows vesicles to be fused to membrane
  4. Integral proteins
    1. float loosely in membrane
      1. Cannot be removed easily without damage
  5. Peripheral proteins
    1. On surface of protein; little movement
      1. Simple removal without damage
  6. Cholesterol
    1. Makes membrane more fluid
  7. Glycoproteins
    1. Body recognition; sticks to other glycoproteins to form tissues
  8. Membrane proteins
    1. Hormone binding sites
      1. Allows hormone to bind to site of protein
        Signal transmitted to inside of cell
    2. Enzymes
      1. Catalyse reactions
        AS outside: catalysed outside
        AS inside: catalysed inside
    3. Glycoproteins
      1. cell-to-cell communication
        cell adhesion
    4. Channels for passive transport
      1. Allows specific substances across membrane
    5. Pumps for active transport
      1. Release energy from ATP
        Used to move specific substances across membrane
Transport
1. Passive
  1. Diffusion
    1. Passive, net movement of particles from a region of higher conc. to a region of lower conc., as a result of the random motion of particles
      1. Simple diffusion
    2. Facilitated diffusion
      1. Channel proteins
        Allow specific substances across the membrane
  2. Osmosis
    1. Passive, net movement of water molecules from a region of low solute conc. to a region of higher solute conc., across a partially permeable membrane
      1. Attractions between water molecules and solute particles
2. Active
  1. Movement of substances across membranes using energy from ATP
    1. Can move substances against concentration gradient
  2. Protein pumps
    1. Different pumps for different substances
      1. Only work in one direction
    2. 1. Particle enters pump from side with lower conc.
      1. 2. Particle binds to specific site
        3. Energy from ATP changes shape of pump
        4. Particle is released on side with higher conc. and pump returns to original shape
3. Vesicles
  1. Transport within cell
    1. Ribosomes synthesise proteins
      1. Proteins enter rER
        Vesicles bud off rER and carry proteins to Golgi apparatus
        Vesicles bud off Golgi apparatus and carry mod. proteins to plasma membrane
  2. Endocytosis
    1. Part of plasma membrane is pulled inward with subs. on outside
      1. Subs. enclosed in vesicle when pinched off
        Vesicle then free to move with contents through cytoplasm
  3. Exocytosis
    1. Vesicle fuses with plasma membrane
      1. Contents of vesicle expelled
        Membrane flattens out

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IB SL Biology: Membranes

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