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•  Cholesterol is a component of animal cell membranes

Cholesterol is a component of animal cell membranes, where it functions to maintain integrity and mechanical stability

  • It is absent in plant cells, as these plasma membranes are surrounded and supported by a rigid cell wall made of cellulose

cholesterol molecule

Cholesterol is an amphipathic molecule (like phospholipids), meaning it has both hydrophilic and hydrophobic regions

  • Cholesterol’s hydroxyl (-OH) group is hydrophilic and aligns towards the phosphate heads of phospholipids
  • The remainder of the molecule (steroid ring and hydrocarbon tail) is hydrophobic and associates with the phospholipid tails

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•  Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes

Phospholipid bilayers are fluid, in that the phospholipids are in constant movement relative to one another

Cholesterol interacts with the fatty acid tails of phospholipids to moderate the properties of the membrane:

  • Cholesterol functions to immobilise the outer surface of the membrane, reducing fluidity
  • It makes the membrane less permeable to very small water-soluble molecules that would otherwise freely cross
  • It functions to separate phospholipid tails and so prevent crystallisation of the membrane
  • It helps secure peripheral proteins by forming high density lipid rafts capable of anchoring the protein

 Cholesterol in Mammalian Membranes

cholesterol membrane