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Other components of the lipid bilayer

Sterols and sugars are also present in the cell membrane.

Sterols such as cholesterol (found only in animals), regulate the fluidity of the membrane. They are scattered across the membrane and occur in varying quantities in different animal cells.

Cholesterol regulates the fluidity of the cell membrane in two ways.

  • Stiffens the membrane

    Cholesterol is a stiff molecule compared to phospholipids and helps to make the membrane stiffer

  • Prevents the membrane from being too stiff

    Cholesterol is randomly dispersed among the hydrophobic tails of phospholipids. This disrupts the orderly packing of the hydrophobic tails, preventing them from crystallizing.

Polysaccharides (sugars) associate with both lipids and proteins to form glycolipids and glycoproteins.

These sugars protrude from the external surface of the cell membrane and act as receptors. They are important in cell recognition and adhesion.

Glycoproteins allow cells to recognise other cells and form tissues (groups of similar cells). Muscle cells identify and adhere to each other to form muscle tissue.