MEMBRANES

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MEMBRANES
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Lipid bilayers keep out large polar molecules
small molecules hydrophobic (uncharged) molecules
outside cell
Inside cell
large molecules polar (charged) molecules
membrane
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Membrane Proteins

• Receptor proteins
• Recognition proteins
• Transport proteins

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Three kinds of membrane proteins
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Recognition Proteins
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Diffusion

• Diffusion is the net movement of molecules down a
  gradient from high to low concentration
• The greater the concentration gradient, the
  faster the rate of diffusion
• If no other processes intervene, diffusion will
  continue until the gradient is eliminated
• Diffusion cannot move molecules rapidly over long
  distances

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Diffusion
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Channel Protein
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Carrier facilitated diffusion
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Carrier-facilitated Diffusion
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Active transport
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Transport Proteins
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Other ways of getting on the other side of a
membrane
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Exocytosis
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Endocytosis
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Vesicle Formation
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Three kinds of endocytosis
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Osmosis

• Is movement of water across a differentially
  permeable membrane
• Water moves from high concentration of free water
  molecules to low concentration
• Dissolved substances reduce the concentration of
  free water molecules

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Osmosis
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Osmosis
Free H2O
Isotonic Solution no net water movement
equal
equal
high
Hypertonic Solution Net water movement out
low
Hypotonic Solution Net water movement in
low
high
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gap junctions
tight junctions