Cholesterol

• Cholesterol molecules exist across the phospholipid bilayer. They add strength to the membranes. They are also very hydrophobic, so play an important role in preventing water and dissolved ion loss from the cell.
• Cholesterol also pulls together the fatty acid tails of the phospholipid molecules, limiting their movement and that of the other molecules without becoming too rigid.
• Cholesterol has a variety of functions within the cell-surface membrane: reducing lateral movement of other molecules including phospholipids, making the membrane less fluid at higher temperatures, and preventing leakage of water and dissolved ions from the cell.