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Lecture

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


Department
Biology
Course Code
BIOL 1202B
Professor
Richard Gardiner

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Membranes
Summary
Proteins in the Plasma Membrane
Membrane must have phospholipids that contain proteins to perform a variety of
functions
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
development
6. Attachment to the cytoskeleton and extracellular matrix
Phospholipids
Made up of phosphate + glycerol (hydrophilic) and 2 fatty acid chains
(hydrophobic)
Types: Micelle (all tails point in), Liposome (inner + outer portions), bilayer (many
phospholipids)
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
fluid
Unsaturated hydrocarbon tails have kinks
Thickness- approx. 1-9 nm
Cholesterol
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
changes
oCold-adapted organisms increase percentage of unsaturated phospholipids in
autumn
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
membrane
Hydrophobic regions with nonpolar amino acid (alpha-helices) that
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