membrane structure

• membranes control what passes through them
• Membranes at the surface of cells (PLASMA membranes)

  • there a barrier between the cell and its environment, controlling which substances enter and leave the cell. partially permeable. substances can move across plasma membrane by diffusion, osmosis or active transport
  • they allow recognition by other cells e.g. cells of the immune system
  • allow cell communication
• membranes within cells

  • membrane around organelles divide cell into different compartments - act as a barrier between organelle and cytoplasm, makes functions more efficient e.g. substances needed for respiration are kept inside mitochondria
  • can form vesicles to transport substances between different areas of cell
  • control which substances enter and leave the organelle
  • can also get membranes within organelles - act as barriers between membrane contents and rest of organelle
  • membrane in cells can be site of chemical reactions
• Phospholipids -

  • hydrophilic head ( polar )
  • hydrophobic tail ( non polar )
  • separate's internal and external layer
  • non polar substances can dissolve through
  • gives flexibility
• cholesterol -

  • present in all cell membranes
  • fit between phospholipids and binds to their tail
  • prevents phospholipids packaging to closely
  • makes membrane less fluid and more rigid
  • lower temps prevents phospholipids packaging closely and increases fluidity
  • maintains stability
• fluid mosaic model - phospholipid free to move and proteins embedded in bilayer with varying size and shape
• roles :

  • compartmentalisation
  • site of biochemical reactions
  • allows cell to change shape
  • allows cell signalling
  • allows movement in and out of cell
• label the diagram of a fluid mosaic model

  A) glycoprotein

  B) glycolipid

  C) phospholipids

  D) protein channel

  E) cholesterol

  F) protein