Week 1

Phospholipids

Molecules that consist of a polar head group and two fatty acid tails; they are fundamental components of cell membranes.

Polar head group

The hydrophilic part of phospholipids that interacts with water.

Fatty acid tails

Hydrophobic components of phospholipids, which can be saturated or unsaturated.

Micelles

Structures formed by phospholipids in water, where the hydrophilic heads face outwards and hydrophobic tails face inwards.

Bilayer

A double layered structure that phospholipids can form in aqueous environments, essential for cell membrane formation.

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

A model that describes the structure and behavior of cell membranes, highlighting lipid bilayers with embedded proteins that can move laterally

• 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

Lateral diffusion

The movement of proteins and lipids within the membrane plane, allowing them to move sideways.

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

Membrane permeability order

The ease with which molecules can pass through a membrane: small nonpolar uncharged, small charged, large nonpolar uncharged, large charged, ions cannot cross.

Saturation of fatty acids

Refers to whether fatty acid chains have double bonds (unsaturated) or are fully hydrogenated (saturated), affecting membrane fluidity.

Hydrogenation

The process of converting unsaturated fats into saturated fats by adding hydrogen, which makes them solids at room temperature.

Liposomes

artificially generated membrane bound vesicles, simple

Membrane permeability affected by temperature

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

Membrane permeability affected by 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 of lipids

• 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