Cholesterol in the cell membrane is located primarily within the phospholipid bilayer, intercalated among the fatty acid tails rather than free in the aqueous compartments. It sits with its hydroxyl (OH) group near the phospholipid headgroups, while the rigid steroid rings align with the hydrophobic core of the membrane, helping to modulate fluidity and permeability. Key points
- Location: Cholesterol spans the bilayer with its hydroxyl group close to the membrane surface and its hydrophobic ring system embedded among the fatty acyl chains of phospholipids. This arrangement stabilizes the membrane and supports its fluid nature across temperatures.
- Orientation: Cholesterol can tilt and reorient rapidly within the bilayer, but its overall position is within the hydrophobic core rather than in the aqueous exterior or interior.
- Functional impact: By disrupting lateral packing of phospholipids, cholesterol reduces membrane permeability to small, water-soluble molecules and buffers membrane fluidity against temperature changes, acting as a “fluidity buffer.”
If you’d like, I can tailor this to a specific cell type or membrane composition (e.g., phospholipid species, presence of sphingolipids or cholesterol-rich rafts) and include how cholesterol distribution might differ in model membranes versus native plasma membranes.
