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Biology 1202B Lecture Notes - Fluid Mosaic Model, Lipid Bilayer, Unsaturated Hydrocarbon

Course Code
BIOL 1202B
Richard Gardiner

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Proteins in the Plasma Membrane
Membrane must have phospholipids that contain proteins to perform a variety of
1. Transport – may or may not involve energy
2. Enzymatic Activity – number of enzymes are actually membrane proteins
3. Signal Transduction – receptors
4. Intercellular Joining – tight junctions, etc.
5. Cell-Cell Recognition – identifying foreigners by orientation/sensing each other for
6. Attachment to the cytoskeleton and extracellular matrix
Made up of phosphate + glycerol (hydrophilic) and 2 fatty acid chains
Types: Micelle (all tails point in), Liposome (inner + outer portions), bilayer (many
Bilayers are studied by separating the 2 layers (bumps and matching concavities
show proteins)
Fluid Mosaic Model
Hydrophilic regions of proteins/phospholipids are in maximum contact with water,
hydrophobic regions are in a nonaqueous environment
Fluidity of Membranes
Membrane molecules are held in place by relatively weak hydrophobic interactions
oMost lipids and some proteins can drift laterally
Phospholipids are quick/ larger proteins are slow (directed manner may
be due to motor proteins of the cytoskeleton) or don’t move at all
(anchored by cytoskeleton)
Red and green membrane proteins mix freely in experiment
Influenced by temperature (cooling makes the membrane less fluid)
oMembranes rich in unsaturated fatty acids (contain double bonds) are more
Unsaturated hydrocarbon tails have kinks
Thickness- approx. 1-9 nm
Amount varies by type of membrane (plasma has 1 per phospholipid
molecule/others have none)
Cells can alter membrane lipid composition to compensate for temperature
oCold-adapted organisms increase percentage of unsaturated phospholipids in
oAlso can hold phospholipids together when it gets too hot
Membrane Proteins
Determine most of the membrane’s specific functions
oPeripheral Proteins – not embedded in lipid bilayer (loosely bound to the
either surface)
oIntegral Proteins- penetrate hydrophobic core of lipid bilayer, often spanning
Hydrophobic regions with nonpolar amino acid (alpha-helices) that
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