General ---------Biology----------------------------------------------------- ------------------Online-------------------------------- Ch. 8 Membrane Structure and Function

Active transport can pump ionsacross a membrane, "uphill" against their concentration gradient, and in the process generate  voltage.  This ion pumping process is fundamental to

• transfering food energy into ATP (Ch. 9)
• muscle contraction
• nerve impulse transmission

Voltage is a difference in charge (+,  -) on opposite sides of a membrane.  An ion is a charged atom or molecule.  Ions result when substances loose or gain electrons, resulting in an imbalance between the protons and electrons. 

The Figure below illustrate a membrane protein creating a voltage by pumping hydrogen ions (protons) across the membrane using ATP energy.  ATP phosphorylates the protein, and the energy in the phosphate bond is used to change the shape of the protein, which pushes the ion through.

Cellular respiration (Ch. 9) uses proton pumps imbedded in the mitochondrial membrane to create an electrochemical gradient (hydrogen ion gradient) to drive the production of ATP from ADP. 

Nerve cells use membrane proteins to generate voltage in nerve cells in a similar manner.