Phospholipids and the bilayer
Amphipathic molecules form bilayers spontaneously.
Phospholipid structure:
- Phosphate head — polar / hydrophilic (water-loving).
- Two fatty acid tails — non-polar / hydrophobic (water-hating).
In aqueous environments, phospholipids spontaneously self-assemble into a bilayer: tails point inward (away from water), heads point outward (toward water). The bilayer is the foundation of every biological membrane.
Hydrophobic core. The interior of the bilayer is non-polar — small non-polar molecules (oxygen, CO₂) cross easily, while polar molecules (water itself crosses slowly; ions, glucose) need protein channels.
- Phospholipid: head + 2 tails.
- Bilayer forms spontaneously in water.
- Hydrophobic core blocks polar molecules.