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Phospholipids are one of the principle components of cell membranes (in conjunction with membrane proteins)
They are amphipathic molecules, meaning they have clearly discernible hydrophilic and hydrophobic regions
Phospholipids typically share a common basic structure that includes:
- A polar organic molecule (e.g. choline, serine)
- A phosphate group
- A glycerol molecule
- Two fatty acid tails
Structure of Phospholipids:
- Consist of a polar head (hydrophilic) composed of a glycerol and a phosphate molecule
- Consist of two non-polar tails (hydrophobic) composed of fatty acid (hydrocarbon) chains
- Because phospholipids contain both hydrophilic (water-loving) and lipophilic (fat-loving) regions, they are classed as amphipathic
Arrangement in Membranes:
- Phospholipids spontaneously arrange into a bilayer
- The hydrophobic tail regions face inwards and are shielded from the surrounding polar fluids, while the two hydrophilic head regions associate with the cytosolic and extracellular fluids respectively
Properties of the Phospholipid Bilayer:
- The bilayer is held together by weak hydrophobic interactions between the tails
- Hydrophilic / hydrophobic layers restrict the passage of many substances
- Individual phospholipids can move within the bilayer, allowing for membrane fluidity and flexibility
- This fluidity allows for the spontaneous breaking and reforming of membranes (endocytosis / exocytosis)
Membrane Fluidity
Membrane Fluidity
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