The key difference between Nernst potential and membrane potential is that Nernst potential is the potential across a cell membrane that opposes the net diffusion of a particular ion through the membrane, whereas membrane potential is the difference between the electric potential of the interior and the electric potential of the exterior of a biological cell.
Nernst potential and membrane potential are important terms in biochemistry. Often, people use these terms interchangeably, though they have a slight difference.
CONTENTS
1. Overview and Key Difference
2. What is Nernst Potential
3. What is Membrane Potential
4. Nernst Potential vs Membrane Potential in Tabular Form
5. Summary – Nernst Potential vs Membrane Potential
What is Nernst Potential?
Nernst potential (also named as reversal potential) is the potential across a cell membrane that opposes the net diffusion of a particular ion through the membrane. This term has its major applications in biochemistry. In order to determine the Nernst potential, we can use the ratio of the concentrations of that specific ion (which is trying to pass through the cell membrane) inside the cell and outside the cell. In addition, this term is also useful in electrochemistry regarding electrochemical cells. The equation that we use to determine the Nernst potential is the Nernst equation.
Nernst equation is a mathematical expression that shows us the relationship between the reduction potential and the standard reduction potential of an electrochemical cell. This equation was named after the scientist Walther Nernst. Moreover, the Nernst equation depends on the other factors affecting electrochemical oxidation and reduction reactions, such as temperature and chemical activity of the chemical species that undergo oxidation and reduction.
When deriving the Nernst equation, we have to consider the standard changes in Gibbs free energy that is associated with electrochemical transformations that occur in the cell. The reduction reaction of an electrochemical cell can be given as follows:
Ox + z e– ⟶ Red
In thermodynamics, the actual free energy change of the reaction is,
E = Ereduction – Eoxidation
We can relate the Gibbs free energy(ΔG) to the E (potential difference) as follows:
ΔG = -nF
Where n is the number of electrons transferred between chemical species when the reaction is progressing, F is the Faraday constant. If we consider the standard conditions, then the equation is as follows:
ΔG0 = -nFE0
We can relate Gibbs free energy of non-standard conditions with the Gibbs energy of standard conditions via the following equation.
ΔG = ΔG0 + RTlnQ
Then, we can substitute the above equations into this standard equation to get the Nernst equation as follows:
-nFE = -nFE0 + RTlnQ
Then the Nernst equation is as follows:
E = E0 – (RTlnQ/nF)
What is Membrane Potential?
Membrane potential (also known as transmembrane potential or membrane voltage) is the difference between the electric potential of the interior and the electric potential of the exterior of a biological cell. Among them, the exterior electric potential of a cell is usually given in the unit of millivolts (mV), and the value ranges from -40 mV to -80 mV.
In biology, all animal cells have a surrounding membrane that consists of a lipid bilayer containing proteins that are embedded in the bilayer. This membrane can act as an insulator and as a diffusion barrier that holds the movement of ions. There are transmembrane proteins that act as ion transporters or ion pumps. They can actively push ions across the membrane, establishing a concentration gradient across the membrane. These ion pumps and ion channels are electrically equivalent to a set of batteries and resistors. Therefore, these components can create a voltage between the two sides of the membrane.
Almost all plasma membranes have an electrical potential across the membrane, having a negative charge on the inside and a positive charge on the outside. There are two basic functions of this electrical potential: allowing a cell to function as a battery and transmission of signals between different parts of a cell.
What is the Difference Between Nernst Potential and Membrane Potential?
Nernst potential and membrane potential are important terms in biochemistry. Often, people use them interchangeably, though they have a slight difference. The key difference between Nernst potential and membrane potential is that the Nernst potential is the potential across a cell membrane that opposes the net diffusion of a particular ion through the membrane, whereas membrane potential is the difference between the electric potential of the interior and the electric potential of the exterior of a biological cell.
Summary – Nernst Potential vs Membrane Potential
Nernst potential and membrane potential are important terms in biochemistry. The key difference between Nernst potential and membrane potential is that the Nernst potential is the potential across a cell membrane that opposes the net diffusion of a particular ion through the membrane, whereas membrane potential is the difference between the electric potential of the interior and the electric potential of the exterior of a biological cell.
Reference:
1. “Membrane Potential (Resting Membrane Potential).” Khan Academy.
Image Courtesy:
1. “Basis of Membrane Potential” By Synaptidude (CC BY 3.0) via Commons Wikimedia