Electrochemical gradient

The electrochemical gradient generated by different concentrations of charged particles ( ions).

Because the charge of the ions pass two gradients combined on:

• Chemical gradient ( concentration gradient ): particles move randomly and tend to have a uniform distribution ( Brownian molecular motion).
• Electrical gradient ( Voltage ): Voltage differences tend to compensation.

If the electrochemical gradient of an ion is equal to zero, so the ion is not committed even at existing concentration gradient and / or existing electric gradient to follow one of these gradients. This is due to the counterrotation of the slope ( gradient ) and their balance.

Electrochemical gradient in biological systems

In biological systems, the electrochemical gradient of the membranes occurs.

Examples are:

• The proton gradient (pH gradient) on mitochondria and chloroplasts, which contributes in the respiratory chain and in photosynthesis for the regeneration of ATP.
• The electrochemical gradient of K through the membrane of nerve cells, which is important for the resting potential in the excitation line.

Proton gradient across the mitochondrial membrane

→ Main article: respiratory chain

By far the most important systems in the ATP regeneration of organisms based on proton, in the respiratory chain and in photosynthesis. A high energy dietary or sunlight gives the organism electrons whose energy is first converted into a proton potential over the inner mitochondrial membrane. This is attributable to the respiratory chain, wherein H - pumps are used, which are operated with high-energy electrons. Caused by the proton gradient driving force which drives the protons now to the ATP synthase which produces ATP.

K gradient across the membrane of nerve cells

→ Main article: resting membrane potential of electrically excitable nerve cells

We will show an example of how the two gradients ( electrical gradient and concentration gradient ) work together.

K is present in the nerve cell near its electrochemical equilibrium, and is mainly responsible for the occurrence of the electrical resting potential of -70 mV across the membrane.

In the cell there are negatively charged organic molecules, such as many proteins and enzymes. Suppose in a cell are so many K ions to compensate this negative charge straight and the membrane potential is 0 mV. K now follows the driving force of the concentration gradient and is striving to leave the cell. The more K ions to leave the cell, the more effect the electrical driving force of the negatively charged organic molecules in the cell to K . These endeavors to pull K back into the cell.

It turns soon, an equilibrium between the two counter- acting driving forces. The electrochemical gradient of K is then equal to 0, and the net flux of K across the membrane stops. This results in the membrane potential of -70 mV, and a higher concentration of K in the cell than outside the cell. This example thus shows the difference between the concentration gradient, electrical gradient (which is equivalent to the electric power ) and the electro-chemical gradient.