These electron carriers are sites of redox reactions for electrons and with each reaction across the electron carriers the electrons energy is transferred into the pumping of hydrogen ions across the membrane, this results in a high concentration in the intermembranal space than that of the matrix.
The protons go through the ATPsynthase from an area of high concentration in the intermembranal space to an area of lower concentration, the mitochondrial matrix, through facilitated diffusion generating ATP. The proton-motive force is the mathematical sum of the chemical gradient, expressed as the difference in pH between the matrix and intermembranal space, and the charge gradient created by the disequilibrium via proton pumping of proton distribution either side of the inner membrane.
The source of this electron is from the photolysis of water, which also generates protons needed for chemiosmosis. During the previous steps of respiration, especially the Krebs cycle, the reduction of co-enzymes plays a pivotal role as a supply of electrons and protons for the electron transport chain and producing the proton-motive force.
In both plants and animals, oxygen is used as the most common final electron acceptor so that the electron transport chain can continue so that chemiosmosis and production of ATP can continue. This was a radical proposal at the time, and was not well accepted. The prevailing view was that the energy of electron transfer was stored as a stable high potential intermediate, a chemically more conservative concept.
The problem with the older paradigm is that no high energy intermediate was ever found, and the evidence for proton pumping by the complexes of the electron transfer chain grew too great to be ignored. Eventually the weight of evidence began to favor the chemiosmotic hypothesis, and in Peter Mitchell was awarded the Nobel Prize in Chemistry. The movement of ions across the membrane depends on a combination of two factors: Diffusion force caused by a concentration gradient - all particles tend to diffuse from higher concentration to lower.
Anions diffuse spontaneously in the opposite direction. These two gradients taken together can be expressed as an electrochemical gradient. Lipid bilayers of biological membranes , however, are barriers for ions. This is why energy can be stored as a combination of these two gradients across the membrane. A random arrangement would not result in a net gradient of protons and therefore, no proton-motive force for the synthesis of ATP. Compounds called uncouplers were found to collapse the pH gradient by shuttling protons back across the membrane through the compounds.
One such uncoupler, dinitophenol is shown below. In the presence of the uncoupler electron transport continues, but no ATP synthesis occurs. Can uncoupling of electron transport and ATP synthesis ever be useful to an organism? The answer is probably "Yes. This occurs normally in many in hibernating animals, in newborn humans, and in mammals adapted to the cold.
It occurs in a specialized tissue known as brown adipose tissue. An uncoupling protein called thermogenin can accomplish this uncoupling and thus allow heat to be generated. Mechanistic stoichiometry of mitochondrial oxidative phosphorylation.
Molecular Biology of the Cell. WH Freeman Palgrave Macmillan; Electron transport is not required as long as there is another mechanism for generating a pH gradient.
An asymmetric orientation is a requirement to establish a pH gradient. In most cases the proton-motive force is generated by an electron transport chain which acts as a proton pump, using the Gibbs free energy of redox reactions to pump protons hydrogen ions out across the membrane, separating the charge across the membrane. Over the past several years, Mitchell's chemiosmotic hypothesis has been widely accepted as the mechanism of coupling of electron transport and ATP synthesis.
The electrical potential gradient is about mV  , negative inside N. An intact inner mitochondrial membrane, impermeable to protons, is a requirement of such a model. The oxidation of acetyl coenzyme A acetyl-CoA in the mitochondrial matrix is coupled to the reduction of a carrier molecule such as nicotinamide adenine dinucleotide NAD and flavin adenine dinucleotide FAD. This is why energy can be stored as a combination of these two gradients across the membrane. Eventually the weight of evidence began to favor the chemiosmotic hypothesis, and in Peter Mitchell was awarded the Nobel Prize in Chemistry.
Lipid bilayers of biological membranes , however, are barriers for ions. In mitochondria, the key site of ATP production in oxidative phosphorylation is the inner mitochondrial membrane. Let N denote the inside of a cell, and let P denote the outside.
One such uncoupler, dinitophenol is shown below. Therefore, shining light on this artificial "purple membrane" formed a proton gradient, which was used by the beef heart mitochondrial ATPase to synthesize ATP. An intact inner mitochondrial membrane, impermeable to protons, is a requirement of such a model. Some of the evidence supporting Mitchell's chemiosmotic hypothesis is as follows. This process was also discovered to take place in the thylakoids of chloroplasts as a means of generating ATP and reduced NADP in the light dependent reaction, key products needed for the light independent reaction to generate hexose sugars in plants.
This is why energy can be stored as a combination of these two gradients across the membrane.