Cell membrane structure

• Fluid mosaic model

  • describes the arrangement of molecules in the membrane
  • 'fluid': phospholipids are constantly moving, which allows flexibility
  • 'mosaic': proteins embedded in the bilayer resembles tiles oa a mosaic due to their varying shapes and sizes
• Function of cell membrane:

  • acts as a barrier between the cell and its environment/the organelle and the cytoplasm
  • partially permeable, controls what substances enter and leave the cell
• Phospholipids:

  • hydrophilic head + hydrophobic tail: arranges into a bilayer with the head facing out towards the water and the tail facing in towards the centre
  • the centre of the bilayer is hydrophobic: acts a a barrier to water-soluble substances
• Cholesterol:

  • fits between phospholipid molecules, binding to the hydrophobic tails
  • controls the fluidity of the membrane by reducing lateral movement of phospholipids
  • prevents the membrane from becoming too fluid under warm conditions/too rigid under cool conditions
  • helps maintain shape of animal cells - important for cells that aren't supported by other cells
• Proteins

  • intrinsic: includes channel proteins and carrier proteins, which allow large molecules and ions to pass through the membrane
  • extrinsic: provides structural support, acts as receptors/enzymes
• Glycoproteins:

  • proteins with carbohydrate chains attached
  • helps cells attach to each other to form tissues, acts as receptors for hormones, presents antigens
• Glycolipids:

  • lipids with carbohydrate chains attached
  • helps maintain the stability of the membrane, acts as recognition sites, helps cells attach to each other to form tissues