The components necessary to create bioelectricity

To generate an electrical potential difference charged ions must be differentially distributed in space. Eukaryotic cells of all forms achieve this by dissolving ions in water and separating those ions across a lipid membrane in which those ions are not soluble and may not, therefore, pass.

Water is an excellent solvent because water molecules possess an assymetrical charge distribution. Polar solutes like metal ions, Na+, Ca++, K+ and Cl- in addition to sugars and many amino acids dissolve readily in water.

The diagram represents the means by which charged solutes are prevented from crystalizing when dissolved in water.

 

Lipid membranes may be considered as amongst the most important structural elements of the cell. They partition various water filled compartments including the intracellular and extracellular spaces. The phosphate rich head of individual lipid molecules (shown in yellow) are polar and, therefore, soluble in water. The fatty acid chains are non-polar and interact with fatty acid of other lipid molecules. Consequently, when in contact with water phospholipids will form bilayers as shown in the diagram to the left. These bilayers are essentially impenetrable by ions dissolve in water.

Proteins are comprised of sequences of amino acids that fold to form secondary structures (for example alpha helices that may be more soluble in water or in lipid). Different secondary structures fold to form tertiary structure or protein subunits that may in some cases span membranes. Such subunits may combine to form tertiary structures that may complete ion channels are transmembrane pumps.

Properties of pumps
Utilize energy (ATP) to move ions against their electrochemical gradient
Selective between ions

Ion channel properties
Selective between ions
Allow ions to move across membranes down their electrochemical gradient
May be activated, gated

 

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