Diffusion of Ions Through Cell Membrane

 

  • Due to their large size (all ions in solution are hydrated) as well as their charge, ions cannot diffuse through the cell membrane.
  • Ions enter the cell membrane through ion channels composed of proteins that span the cell membrane.
  • These channels are usually highly selective i.e. they will let through only one type of ion or a small number of ions.
  • This selectively is due the

    1. diameter of channel
    2. internal charge
    3. length of channel
    4. shape of internal channel
    • Certain channels are gated.
    • By gated, one means that the channels are either open or closed.
    • These gates are either controlled through chemical signals (ligand gated) or by electrical changes (voltage gated)
    • Though utilising protien channels, the ions would still be diffusing down their concnetration gradient and hence there is no energy expenditure.