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Lecture 22 (Cell Membrane Proteins (responsible for a wide variety of…

- - - - i.e. glycoproteins and oligosaccharides can only be found in the extracellular compartment of the membrane.
- - - - membrane-associated proteins are able to move within the membrane.
        
        G-protein subunits in the intracellular compartment of the cell membrane move freely within the cell upon activation.
      - Lipids are also able to move within the membrane.
        
        phospholipids that compose the lipid bilayer can migrate rapidly in the plane of the membrane, as it is a 2-dimensional fluid.
        
        however, "flip-flopping' between top and bottom layers is rare as it is not energetically favourable
- - - - unsaturated
        fatty acids
        
        has double bonds that create a "kink" along the length of the chain.
        
        causes structural changes that weaken close-range hydrophobic interactions, making the membrane more fluid.
      - saturated
        fatty acids
        
        no double bonds which allow for a relatively stable, straight structure.
      - Hydrophobic hydrocarbon tails are 16-22 carbon long fatty acid chains.
    - - cholesterol helps stiffen human membranes ─ membrane becomes less fluid.
    - - heat increases entropy, which results in the deterioration of cell membrane integrity → more fluid.
      - also, hydrophobic interactions that stabilise the phospholipid tails are easy to destabilise through temperature b/c they are weak.
      - The melting temperature of fatty acids tells you something about the strength of their hydrophobic interactions.
        
        the higher it is, the stronger the interaction → more energy required to melt the structure.
        
        the lower it is, the weaker the interactions → more fluid the lipid.
        
        also related to chain length ─ more carbons = stronger interactions = higher melting point.
- - - - composed of both polar (phosphates) and nonpolar (fatty acids) molecules.
      - forms compartmentalised bilayers in aqueous environments
    - - a range of polar groups may be attached to the phosphate head.
        
        allows for functional diversity at the membrane
        
        transport
        
        structural support
        
        binding
  - - - based on amino alcohols (sphingosines) instead of glycerol.
      - abundant in myelin sheaths around neurons
    - - side chains are attached by glycosidic linkages
      - common in plants.