An electron transport chain is a series of protein complexes in cells that couple redox reactions to create an electrochemical gradient that is required to generate ATP. This process occurs within the mitochondria during cellular respiration. During this process, electrons are released after breaking down organic molecules. The energy released is used to build carbohydrates. This process is vital to life. This article will explain how electrons move from one place to another in the electron transport chain.
Coenzyme Q
Coenzyme Q is an important component of the electron transport chain. It is an enzyme that moves electrons through a series of iron-sulfur clusters. Ubiquinone (ubiquinol) is the product of this transfer. In the mitochondria, ubiquinone extracts two protons from the matrix and transfers them to coenzyme Q. The resulting product is ubiquinol, which is a form of fully reduced ubiquinol (QH2). This process uses the electrical energy provided by the electrons to pump four H+ ions out of the matrix of the mitochondria and into the intermembrane space. This process is necessary for the production of ATP.
Coenzyme Q is synthesized in most human tissues. The biosynthesis of coenzyme Q involves three major steps. The first step is acquiring the benzoquinone structure, which is derived from phenylalanine and tyrosine. The second step is generating the polyisoprenoid side chain, which can react with oxygen to produce superoxide anion.
Coenzyme Q is an essential cofactor of the electron transport chain and an endogenous antioxidant. Its depletion by lipid peroxidation results in the inactivation of respiratory chain enzymes. Coenzyme Q10 supplementation has been shown to maintain mitochondrial respiratory function in aged rat skeletal muscle. The antioxidant properties of coenzyme Q are also important in the process of aging.
NADH
The two major components of the electron transport chain, NADH and FADH2, are rechargeable. When fully charged, they can power many devices, including radios and flashlights. The two molecules transfer electrons to the electron transport chain, a collection of proteins embedded in the inner membrane of mitochondria.
This process occurs in a biochemical process called glycolysis. The process yields approximately two net ATP from the citric acid cycle and the rest comes from oxidative phosphorylation. In the first step of glycolysis, four H+ ions must be pumped through an enzyme known as ATP synthase. The second step requires the pumping of 10 H+ ions from NADH, which yields about 2.5 ATP per unit.
The electron transport chain is a complex series of proteins embedded in the inner membrane of mitochondria. Each complex in the ETC accepts two electrons donated by NADH. As the electrons move down the chain, they deposit protons into the intermembrane space, where they are eventually accepted by oxygen.
The electrons from NADH travel to the next complex by the same route as FADH2. The cellular electron transport chain is made up of three electron carriers. The first two are called complex I and complex II, while the last two are known as complex III and complex IV. Each of the three carriers in complex I has a higher electronegativity than the others.
Ubiquinone
Ubiquinone is a component of the electron transport chain of Pseudomonas aeruginosa. Its level in the membranes ranged from 36-43% in the aerobic steady state, 65% in anaerobic states, and 81% in the presence of a mixture of substrates.
Ubiquinone is a type of coenzyme and belongs to the family of the coenzyme Qs. Its chemical structure is made up of a head group (benzoquinone) that accepts electrons and a tail (isoprenyl). Ubiquinones are found in all respiring eukaryotic cells and participate in the electron transport chain. It is also an antioxidant, scavenging free radicals.
Ubiquinone is a lipid soluble benzoquinone that is localized in mitochondria. This compound undergoes cyclic oxidation-reduction during the citric acid cycle. However, its rate of reduction is not sufficient to account for the entire electron flux in the system. When ubiquinone is depleted by treatment with acetone, the mitochondria fail to function as an electron transporter. In order to restore this function, ubiquinone must be replaced with its homologue.
Cytochrome c oxidase
Cytochrome c oxidases are important components of the respiratory chain, and are involved in the transfer of electrons from cytochrome c to oxygen. They are found in the mitochondrial inner membrane and the plasma membrane. They are composed of three copper ions, one of which is CuA and one of which is CuB. These ions form complex IV, which then binds four protons from the inner aqueous phase. In the process, the cytochrome c oxidase transfers one electron to oxygen, converting it into two molecules of water.
This enzyme pumps a proton out of the inner mitochondrial membrane, and reduces O2. This is necessary for ATP synthesis. Cytochrome c oxidases also reduce O2 and serve as the final electron acceptor in the electron transport chain.
Cytochrome c oxidases encode for up to eight smaller subunits. Some are organ-specific, such as subunit VIa in the heart. This difference is thought to affect the efficiency of proton pumping in the heart and liver.
Ubiquinol reduction
The ubiquinols in the cell play a major role in recycling electrons. As a result, they are responsible for donating two electrons back to the electron transport chain. The first electron is sent to a cluster of FeS molecules, and the second one is sent to the iron heme center. The second electron is then sent back to the matrix, and the ubiquinone UQ awaits an electron from the heme BL.
Ubiquinone, which is the oxidized form of Coenzyme Q10, is also transferred to the inner mitochondrial membrane by Complex I. This is a step in the electron transport chain, and ubiquinol is reduced to ubiquinol H2 and transferred to the cellular membrane. The ubiquinol in the electron transport chain undergoes single-electron reduction with O2, which is then converted to H2O2 by manganese superoxide dismutase.
Ubiquinol is a lipid-soluble, mobile electron carrier that is found in high concentrations on the inner membrane of the mitochondrion. It plays a critical role in the electron transport chain of aerobic metabolism. Ubiquinol reduction is a complex process, involving two single electron transfers. Due to its resonance stabilization, the reduced ubiquinol molecule is relatively stable.
