The fluid mosaic model, proposed by Singer and Nicolson in 1972, describes the structure of all cell membranes.It is fluid because the phospholipids and many of the proteins can move sideways within the bilayer, so the membrane is flexible and constantly changing, rather than a fixed sheet.It is a mosaic because the proteins are scattered through the bilayer in an irregular pattern, like tiles in a mosaic, when seen from above.
• a phospholipid bilayer, with hydrophilic heads outwards and hydrophobic tails inwards
• intrinsic and extrinsic proteins, including channels and carriers
• glycoproteins and glycolipids, with carbohydrate chains on the outer surface, used for cell recognition and as receptors
• cholesterol molecules between the phospholipids (in animal cells)Cholesterol regulates fluidity. It binds to fatty acid tails and packs between them, which reduces movement at higher temperatures and keeps the membrane stable. At low temperatures it stops the tails packing too closely, so the membrane does not become too rigid. It also makes the membrane less permeable to water-soluble substances.Evidence and temperature. Fluidity rises with temperature. At high temperatures the phospholipids move so much, and membrane proteins are denatured, that the membrane becomes much more permeable. This is why the red pigment leaks out of beetroot faster at higher temperatures.
• a phospholipid bilayer, with hydrophilic heads outwards and hydrophobic tails inwards
• intrinsic and extrinsic proteins, including channels and carriers
• glycoproteins and glycolipids, with carbohydrate chains on the outer surface, used for cell recognition and as receptors
• cholesterol molecules between the phospholipids (in animal cells)Cholesterol regulates fluidity. It binds to fatty acid tails and packs between them, which reduces movement at higher temperatures and keeps the membrane stable. At low temperatures it stops the tails packing too closely, so the membrane does not become too rigid. It also makes the membrane less permeable to water-soluble substances.Evidence and temperature. Fluidity rises with temperature. At high temperatures the phospholipids move so much, and membrane proteins are denatured, that the membrane becomes much more permeable. This is why the red pigment leaks out of beetroot faster at higher temperatures.