Cholesterol is a conjugated lipid which is present in the cell membrane of the eukaryotic cells. It is responsible for maintaining the integrity of the cell membrane. Also, it helps to secure proteins within the membrane and acts as a bidirectional regulator of membrane fluidity.
Interaction with cholesterol will result in the decreases in the movement of hydrophobic (carbon containing) phospholipid tails. In the solid state, fatty acid tails’ packing is disturbed due to the presence of cholesterol in the phospholipid membrane. This prevents its change into the crystalline state.
| Cholesterol enters the two-layered membrane when the placement of its hydroxyl group is towards the aqueous phase and the placement of its hydrophobic ring system is adjacent to phospholipids’ fatty acid tails. Hydrogen bonds are formed between polar heads of phospholipid and cholesterol’s hydroxyl group. |
This results in lowering the movement of the peripheral parts of the fatty acid chains, making this portion of the membrane tougher. However, presence of cholesterol disturbs the reactions between fatty acid chains. Therefore, it helps in maintaining membrane fluidity at lower temperatures.