Week 1

Basic structure of phospholipids:

• Polar head group (hydrophilic)

• Two fatty acid tails, one bent with cis double bond (hydrophobic)

In water phospholipids may self-assemble into…

• Micelles

• Bilayer

Fluorescence Recovery After Photobleaching (FRAP):

• Phospholipids in cells labelled with fluorescent molecules

• Small region bleached with laser beam

• Observes how quickly the fluorescence recovers

• Faster recovery indicates faster diffusion/mobility

Fluid-Mosaic Model

• Discovered by freeze fracture:

  • Freeze membrane

  • Fracture sample with knife along lines of least resistance

  • Coat sample with thin film of heavy metals/carbon

  • Use electron microscopy to observe

• Proteins move:

  • Lateral diffusion

  • Cannot flip-flop

  • Can rotate around axes

  • Membrane fusion experiment: fused mouse and human cell after fluorescence labeling for identification, observed antibodies (proteins) mixed on membrane of fused cell (heterokaryon) showcasing proteins move

Across synthetic lipid bilayer..

• Order of ease of passing: small nonpolar uncharged, small charged, large nonpolar uncharged, large charged, ions cannot cross

Membrane permeability affected by…

• Temperature: when low, fluidity decreases, molecule movement slows, hydrophobic tails pack closer together (decreases lateral mobility)

• Saturation: Saturated chains have less space/stronger hydrophobic interactions causing decreased fluidity. Unsaturated creates kinks, preventing close packing/reducing hydrophobic interactions hence increasing fluidity.

Fatty acids: simple lipids with hydrocarbon chains

• Double bonds in plane and cannot rotate while single bonds table and 3D tetrahedrals

• Saturation: saturated are solid, unsaturated are liquids (converted to saturation by hydrogenation)

Lipids: carbon containing compounds insoluble in water, 3 types

• Steroids: has four carbon rings structures, differences in R-groups

• Fats: for energy storage, nonpolar molecules with 3 fatty acids linked to glycerol

• Fatty acid and glycerol linked by ester linkage (two atoms linked by O)

• Fats from when dehydration between OH groups of hydroxyl + carbonyl group of free fatty acid occurs

• Phospholipids 

Liposomes: artificially generated membrane bound vesicles