Roles and structures of membranes

• Phospholipid


  Control the movement of substances

  hydrophilic head faces outwards while hydrophobic tails face inwards forming a bilayer
• Cholesterol


  Regulate membrane fluidity

  hydrophobic lipid molecule

  helps cell from leaking water and dissolved ions
• Glycolipids


  Acts as a recognition site for other cells

  chemical receptors

  cell stability and attachment
• Surface proteins


  Provide mechanical support
• Glycoproteins- extrinsic


  Act as recognition sites for foreign cells or specific chemicals

  Help with cell attachment

  Receptors like hormones and neurotransmitters
• Transport proteins


  Help transport substances
• Proteins


  Mechanical support
• Channel protein- intrinsic


  Water filled and transports water soluble molecules
• Carrier protein- intrinsic


  Active transport

  Attaches to protein and changes its shape to fit

  Uses energy
• How does cholesterol work


  Attaches to fatty acid tails to prevent fluidity especially at high temperatures
• Permeability of the plasma membrane


  Many substances can’t get through (water soluble things) but lipid soluble things can
• What can’t enter

  Large molecules

  Charged molecules

  Polar molecules
• Intrinsic


  Goes through the membrane
• Extrinsic


  At the surface