cholesterol

• Cholesterol has a hydrocarbon ring structure attached to a hydrocarbon tail. The ring structure has a polar hydroxyl (OH) group attached to it.
• structure

  A) hydroxyl group

  B) hydrocarbon rings

  C) hydrocarbon tail

  
• • In eukaryotic cells, cholesterol molecules help to regulate the fluidity of the cell membrane by interacting with the phospholipid bilayer.
  • Cholesterol has a small size and flattened shape - this allows cholesterol to fit in between the phospholipid molecules in the membrane.
  • At higher temperatures, they bind to the hydrophobic tails of the phospholipids, causing them to pack more closely together. This helps to make the membrane less fluid and more rigid.
  • At lower temperatures, cholesterol prevents phospholipids from packing too close together, and so increases membrane fluidity.