lecture0305final - Membrane fluidity lipid fluidity Each...

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Membrane fluidity – lipid fluidity Each membrane has a unique  transition temperature, T c  at which  the membrane “freezes” -  transforms from a gel to a liquid.
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Figure 4.23
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Figure 4.24
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Membrane fluidity – lipid fluidity T varies from membrane to membrane  according to environment and functional  needs Lower T c    more fluid bilayer at room  temperature (further from “freezing”). High % of  unsaturated fatty acid chains  (more double bonds) or short fatty acid  chains --> lower T    ---  “more fluidity” High cholesterol content also broadens  the temperature range over which gelling  occurs – creating an“intermediate fluidity”  in the temperature range
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Maintaining or changing lipid fluidity    Lipid fluidity can be controlled by  synthesizing new phospholipids with  different fatty acid properties or  remodeling existing phospholipid fatty  acid chains using enzymes that  insert/remove double bonds in the chain     Fluidity can be maintained constant at  different temperatures by this means –  important in cold-blooded animals, like  pond dwelling fish which experience  extremes of temperature.    Reduced temperatures in winter require a  lower T c  to maintain membrane fluidity  and so more unsaturated phospholipids  are inserted into cell membranes
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Lipid asymmetry Lipids with different headgroups (or  different lipids entirely) are often found in  each leaflet of the membrane E.g. sphingomyelin – extracellular Phosphatidylcholine – extracellular Phosphatidylserine  - intracellular 
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lecture0305final - Membrane fluidity lipid fluidity Each...

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