The electron transport chain in the mitochondrion is the site of oxidative phosphorylation in eukaryotes. The NADH and succinate generated in the citric acid cycle is oxidized, releasing energy to power the ATP synthase.

Oxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate (ATP). Although the many forms of life on earth use a range of different nutrients, almost all carry out oxidative phosphorylation to produce ATP, the molecule that supplies energy to metabolism. This pathway is probably so pervasive because it is a highly efficient way of releasing energy, compared to alternative fermentation processes such as glycolysis. Image File history File links Mitochondrial_electron_transport_chain—Etc4. ... Image File history File links Mitochondrial_electron_transport_chain—Etc4. ... The Electron Transport Chain. ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... Overview of the citric acid cycle The citric acid cycle (also known as the tricarboxylic acid cycle, the TCA cycle, or the Krebs cycle, after Hans Adolf Krebs who identified the cycle) is a series of chemical reactions of central importance in all living cells that use oxygen as part... An ATP synthase (EC 3. ... In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell. ... ed|other uses|reduction}} Illustration of a redox reaction Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... A nutrient is a substance used in an organisms metabolism which must be taken in from the environment. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... For other uses, see Fermentation. ... Glycolysis is the sequence of reactions that converts glucose into pyruvate with the concomitant production of a relatively small amount of ATP. The word is derived from Greek γλυκύς (sweet) and λύσις (letting loose). ...

During oxidative phosphorylation, electrons are transferred from electron donors to electron acceptors such as oxygen, in redox reactions. These redox reactions release energy, which is used to form ATP. In eukaryotes, these redox reactions are carried out by a series of protein complexes within mitochondria, whereas in prokaryotes, these proteins are located in the cells' inner membranes. These linked sets of enzymes are called electron transport chains. In eukaryotes, five main protein complexes are involved, whereas in prokaryotes many different enzymes are present, using a variety of electron donors and acceptors. A reducing agent (also called a reductant or reducer) is the element or a compound in a redox (reduction-oxidation) reaction (see electrochemistry) that reduces another species. ... European Union Chemical hazard symbol for oxidizing agents Dangerous goods label for oxidizing agents Oxidizing agent placard An oxidizing agent (also called an oxidant or oxidizer) is A chemical compound that readily transfers oxygen atoms or A substance that gains electrons in a redox chemical reaction. ... This article is about the chemical element and its most stable form, or dioxygen. ... The most fundamental reactions in chemistry are the redox processes. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... A protein complex is a group of two or more associated proteins formed by protein-protein interaction that is stable over time. ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ... Prokaryotic bacteria cell structure Prokaryotes (IPA: //) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. ... The Electron Transport Chain. ...

The energy released as electrons flow through this electron transport chain is used to transport protons across the inner mitochondrial membrane, in a process called chemiosmosis. This generates potential energy in the form of a pH gradient and an electrical potential across this membrane. This store of energy is tapped by allowing protons to flow back across the membrane and down this gradient, through a large enzyme called ATP synthase. This enzyme uses this energy to generate ATP from adenosine diphosphate (ADP), in a phosphorylation reaction. Unusually, the ATP synthase is driven by the proton flow which forces the rotation of a part of the enzyme—it is a rotary mechanical motor. Mitochondria structure: (1) inner membrane, (2) outer membrane, (3)cristae, (4) matrix The mitochondrial inner membrane forms internal compartments known as cristae, which allow greater space for the proteins such as cytochromes to function properly and efficiently. ... Chemiosmosis is the diffusion of ions across a membrane. ... Potential energy can be thought of as energy stored within a physical system. ... For other uses, see PH (disambiguation). ... Membrane potential (or transmembrane potential or transmembrane potential difference or transmembrane potential gradient), is the electrical potential difference (voltage) across a cells plasma membrane. ... Human glyoxalase I. Two zinc ions that are needed for the enzyme to catalyze its reaction are shown as purple spheres, and an enzyme inhibitor called S-hexylglutathione is shown as a space-filling model, filling the two active sites. ... An ATP synthase (EC 3. ... Adenosine diphosphate, abbreviated ADP, is a nucleotide. ... A phosphorylated serine residue Phosphorylation is the addition of a phosphate (PO4) group to a protein molecule or a small molecule. ... This article is about rotation as a movement of a physical body. ...

Although oxidative phosphorylation is a vital part of metabolism, it produces reactive oxygen species such as superoxide and hydrogen peroxide that lead to propagation of free radicals, damaging cells and contributing to disease and, possibly, aging. The enzymes carrying out this metabolic pathway are also the target of many drugs and poisons that inhibit their activities. Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... Reactive oxygen species (ROS) include oxygen ions, free radicals and peroxides both inorganic and organic. ... Lewis electron configuration of superoxide. ... Hydrogen peroxide (H2O2) is a very pale blue liquid which appears colorless in a dilute solution, slightly more viscous than water. ... In chemistry, radicals (often referred to as free radicals) are atomic or molecular species with unpaired electrons on an otherwise open shell configuration. ... This article is about the medical term. ... Ageing or aging is the process of getting older. ... For other uses, see Poison (disambiguation). ... HIV protease in a complex with the protease inhibitor ritonavir. ...

Overview of energy transfer by chemiosmosis

Further information: Chemiosmosis and Bioenergetics

Oxidative phosphorylation works by using energy-releasing chemical reactions to drive energy-requiring reactions: The two sets of reactions are said to be coupled. This means one cannot occur without the other. The flow of electrons through the electron transport chain, from electron donors such as NADH to electron acceptors such as oxygen, is an exergonic process – it releases energy, whereas the synthesis of ATP is an endergonic process that requires an input of energy. Both the electron transport chain and the ATP synthase are embedded in a membrane, and energy is transferred from electron transport chain to the ATP synthase by movements of protons across this membrane, in a process called chemiosmosis.^[1] In practice, this is like a simple electric circuit, with a current of protons being driven from the negative N-side of the membrane to the positive P-side by the proton-pumping enzymes of the electron transport chain. These enzymes are like a battery, as they perform work to drive current through the circuit. The movement of protons creates an electrochemical gradient across the membrane, which is often called the proton-motive force. This gradient has two components: a difference in proton concentration (a pH gradient) and a difference in electric potential, with the N-side having a negative charge. The energy is stored largely as the difference of electric potentials in mitochondria, but also as a pH gradient in chloroplasts.^[2] Chemiosmosis is the diffusion of ions across a membrane. ... Bioenergetics, loosely defined, is the study of energy investment and flow through living systems. ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ... Look up exergonic in Wiktionary, the free dictionary. ... Endergonic means absorbing energy in the form of work. ... Chemiosmosis is the diffusion of ions across a membrane. ... A simple electric circuit made up of a voltage source and a resistor. ... For other uses, see Battery. ... In thermodynamics, work is the quantity of energy transferred from one system to another without an accompanying transfer of entropy. ... In cellular biology, an electrochemical gradient refers to the electrical and chemical properties across a membrane. ... This box:      At a point in space, the electric potential is the potential energy per unit of charge that is associated with a static (time-invariant) electric field. ... This box:      At a point in space, the electric potential is the potential energy per unit of charge that is associated with a static (time-invariant) electric field. ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ...

ATP synthase releases this stored energy by completing the circuit and allowing protons to flow down the electrochemical gradient, back to the N-side of the membrane.^[3] This enzyme is like an electric motor as it uses the proton-motive force to drive the rotation of part of its structure and couples this motion to the synthesis of ATP. For other kinds of motors, see motor. ...

The amount of energy released by oxidative phosphorylation is high, compared with the amount produced by anaerobic fermentation. Glycolysis produces only 2 ATP molecules, but somewhere between 30–36 ATPs are produced by the oxidative phosphorylation of the 10 NADH and 2 succinate molecules made by converting one molecule of glucose to carbon dioxide and water.^[4] This ATP yield is the theoretical maximum value; in practice, some protons leak across the membrane, lowering the yield of ATP.^[5] Look up Fermentation in Wiktionary, the free dictionary. ... Glycolysis is the sequence of reactions that converts glucose into pyruvate with the concomitant production of a relatively small amount of ATP. The word is derived from Greek γλυκύς (sweet) and λύσις (letting loose). ... Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ...

Electron and proton transfer molecules

Further information: Coenzyme and Cofactor

Reduction of coenzyme Q from its ubiquinone form (Q) to the reduced ubiquinol form (QH₂).

The electron transport chain carries both protons and electrons, passing electrons from donors to acceptors, and transporting protons across a membrane. These processes use both soluble and protein-bound transfer molecules. In mitochondria, electrons are transferred within the intermembrane space by the water-soluble electron transfer protein cytochrome c.^[6] This carries only electrons, and these are transferred by the reduction and oxidation of an iron atom that the protein holds within a heme group in its structure. Cytochrome c is also found in some bacteria, where it is located within the periplasmic space.^[7] Coenzyme A Coenzymes are small organic non-protein molecules that carry chemical groups between enzymes. ... A cofactor is any substance that needs to be present in addition to an enzyme to catalyze a certain reaction. ... Image File history File links Ubiquinone–ubiquinol_conversion. ... Image File history File links Ubiquinone–ubiquinol_conversion. ... It has been suggested that this article or section be merged with Solution. ... Cytochrome c with heme c. ... Fe redirects here. ... Structure of Heme b A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. ... The periplasmic space is the space seen between the plasma membrane and the outer membrane in the gram-negative bacteria. ...

Within the inner mitochondrial membrane, the lipid-soluble electron carrier coenzyme Q10 (Q) carries both electrons and protons by a redox cycle.^[8] This small benzoquinone molecule is very hydrophobic, so it diffuses freely within the membrane. When Q accepts two electrons and two protons, it becomes reduced to the ubiquinol form (QH₂); when QH₂ releases two electrons and two protons, it becomes oxidized back to the ubiquinone (Q) form. As a result, if two enzymes are arranged so that Q is reduced on one side of the membrane and QH₂ oxidized on the other, ubiquinone will couple these reactions and shuttle protons across the membrane.^[9] Some bacterial electron transport chains use different quinones, such as menaquinone, in addition to ubiquinone.^[10] Some common lipids. ... Coenzyme Q (CoQ), also known as ubiquinone or ubiquinol, is a biologically active quinone with an isoprenoid side chain, related in structure to vitamin K and vitamin E. The oxidized structure of CoQ, or Q, is given here: The various kinds of Coenzyme Q can be distinguished by the number... ed|other uses|reduction}} Illustration of a redox reaction Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... 1,4-Benzoquinone, also cyclohexa-2,5-diene-1,4-dione, is a ketone, with formula C6H4O2. ... Hydrophobe (from the Greek (hydros) water and (phobos) fear) in chemistry refers to the physical property of a molecule that is repelled by water. ... Hydroquinone, also benzene-1,4-diol, is an aromatic organic compound which is a type of phenol, having the chemical formula C6H4(OH)2. ... Vitamin K1 (phylloquinone). ...

Within proteins, electrons are transferred between flavin cofactors,^[11][3] iron–sulfur clusters, and cytochromes. There are several types of iron–sulfur cluster. The simplest kind found in the electron transfer chain consists of two iron atoms joined by two atoms of inorganic sulfur; these are called [2Fe–2S] clusters. The second kind, called [4Fe–4S], contains a cube of four iron atoms and four sulfur atoms. Each iron atom in these clusters is coordinated by an additional amino acid, usually by the sulfur atom of cysteine. Metal ion cofactors undergo redox reactions without binding or releasing protons, so in the electron transport chain they serve solely to transport electrons through proteins. Electrons move quite long distances through proteins by hopping along chains of these cofactors.^[12] This occurs by quantum tunnelling, which is rapid over distances of less than 1.4×10⁻⁹ m.^[13] Riboflavin Flavin is a vaginal ring whose biochemical smell is pungent. ... This article is about the chemical element. ... This article is about the class of chemicals. ... Cysteine is a naturally occurring, sulfur-containing amino acid that is found in most proteins, although only in small quantities. ... In quantum mechanics, quantum tunnelling is a micro and nanoscopic phenomenon in which a particle violates principles of classical mechanics by penetrating or passing through a potential barrier or impedance higher than the kinetic energy of the particle. ...

Eukaryotic electron transport chains

Further information: Electron transport chain and Chemiosmosis

Many catabolic biochemical processes, such as glycolysis, the citric acid cycle and beta oxidation, produce the reduced coenzyme NADH. This coenzyme contains electrons that have a high transfer potential; in other words, they will release a large amount of energy upon oxidation. However, the cell does not release this energy all at once, as this would be an uncontrollable reaction. Instead, the electrons are removed from NADH and passed to oxygen through a series of enzymes that each release a small amount of the energy. This set of enzymes, consisting of complexes I through IV, is called the electron transport chain and is found in the inner membrane of the mitochondrion. Succinate is also oxidized by the electron transport chain, but feeds into the pathway at a different point. The Electron Transport Chain. ... Chemiosmosis is the diffusion of ions across a membrane. ... Anabolism is the aspect of metabolism that contributes to growth. ... Glycolysis is the sequence of reactions that converts glucose into pyruvate with the concomitant production of a relatively small amount of ATP. The word is derived from Greek γλυκύς (sweet) and λύσις (letting loose). ... Overview of the citric acid cycle The citric acid cycle (also known as the tricarboxylic acid cycle, the TCA cycle, or the Krebs cycle, after Hans Adolf Krebs who identified the cycle) is a series of chemical reactions of central importance in all living cells that use oxygen as part... Coenzyme A Coenzymes are small organic non-protein molecules that carry chemical groups between enzymes. ... It has been suggested that Electrode potential be merged into this article or section. ... Succinic acid, originally called spirit of amber, is a carboxylic acid with the formula: HOOC-CH2-CH2-COOH At room temperature, pure succinic acid is a solid that forms colorless, odorless prisms. ...

In eukaryotes, the enzymes in this electron transport system use the energy released from the oxidation of NADH to pump protons across the inner membrane of the mitochondrion. This causes protons to build up in the intermembrane space, and generates an electrochemical gradient across the membrane. The energy stored in this potential is then used by ATP synthase to produce ATP. Oxidative phosphorylation in the eukaryotic mitochondrion is the best-understood example of this process. The mitochondrion is present in almost all eukaryotes, with the exception of anaerobic protozoa such as Trichomonas vaginalis that instead reduce protons to hydrogen in a remnant mitochondrion called a hydrogenosome.^[14] Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... For other uses, see Proton (disambiguation). ... The intermembrane space is the region between the inner membrane and the outer membrane of a mitochondrion or a chloroplast. ... In cellular biology, an electrochemical gradient refers to the electrical and chemical properties across a membrane. ... Binomial name Trichomonas vaginalis (Donné 1836) Trichomonas vaginalis, an anaerobic, parasitic flagellated protozoan, is the causative agent of trichomoniasis, and is the most common pathogenic protozoan infection of humans in industrialized countries. ... A hydrogenosome is an organelle of ciliates, trichomonads and fungi. ...

NADH-coenzyme Q oxidoreductase (complex I)

Complex I or NADH-Q oxidoreductase. The abbreviations are discussed in the text. In all diagrams of respiratory complexes, the matrix is at the bottom, with the intermembrane space above.

NADH-coenzyme Q oxidoreductase, also known as NADH dehydrogenase or complex I, is the first protein in the electron transport chain.^[15] Complex I is a giant enzyme with the mammalian complex I having 46 subunits and a molecular mass of about 1,000 kilodaltons (kDa).^[16] The structure is known in detail only from a bacterium;^[17] in most organisms the complex resembles a boot with a large “ball” poking out from the membrane into the mitochondrion.^[18][19] The genes that encode the individual proteins are contained in both the cell nucleus and the mitochondrial genome, as is the case for many enzymes present in the mitochondrion. Image File history File links Complex_I.svg‎ File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Complex_I.svg‎ File historyClick on a date/time to view the file as it appeared at that time. ... NADH dehydrogenase NADH dehydrogenase (EC 1. ... NADH dehydrogenase NADH dehydrogenase (EC 1. ... Human glyoxalase I. Two zinc ions that are needed for the enzyme to catalyze its reaction are shown as purple spheres, and an enzyme inhibitor called S-hexylglutathione is shown as a space-filling model, filling the two active sites. ... The unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express atomic and molecular masses. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... The mitochondrial genome is the genetic material of the mitochondria. ...

The reaction which is catalyzed by this enzyme is the two electron reduction by NADH of coenzyme Q10 or ubiquinone (represented as Q in the equation below), a lipid-soluble quinone that is found in the mitochondrion membrane: Nicotinamide adenine dinucleotide (NAD+ or in older notation DPN+) is an important coenzyme found in cells. ... Coenzyme Q (CoQ), also known as ubiquinone or ubiquinol, is a biologically active quinone with an isoprenoid side chain, related in structure to vitamin K and vitamin E. The oxidized structure of CoQ, or Q, is given here: The various kinds of Coenzyme Q can be distinguished by the number... A quinone (or benzoquinone) is either one of the two isomers of cyclohexadienedione or a derivative thereof. ...

The start of the reaction, and indeed of the entire electron chain, is the binding of a NADH molecule to complex I and the donation of two electrons. The electrons enter complex I via a prosthetic group attached to the complex, flavin mononucleotide (FMN). The addition of electrons to FMN converts it to its reduced form, FMNH₂. The electrons are then transferred through a series of iron–sulfur clusters: the second kind of prosthetic group present in the complex.^[17] There are both [2Fe–2S] and [4Fe–4S] iron–sulfur clusters in complex I. A prosthetic group is a non-protein (non-amino acid) component of a conjugated protein. ... Flavin mononucleotide or FMN is derived from riboflavin (vitamin B2) and functions as cofactor of various oxidoreductases. ... An iron-sulfur cluster is a structural motif found in certain metalloproteins, such as the ferredoxins, as well as NADH dehydrogenase and Coenzyme Q - cytochrome c reductase of the electron transfer system. ...

As the electrons pass through this complex, four protons are pumped from the matrix into the intermembrane space. Exactly how this occurs is unclear, but it seems to involve conformational changes in complex I that cause the protein to bind protons on the N-side of the membrane and then move them onto the P-side of the membrane.^[20] Finally, the electrons are transferred from the chain of iron–sulfur clusters to a ubiquinone molecule in the membrane.^[15] Reduction of ubiquinone also contributes to the generation of a proton gradient, as two protons are taken up from the matrix as it is reduced to ubiquinol (QH₂). In molecular biology, a protein may change its shape in order to undertake a new function; each possible shape is called a conformation, and a transition between them is called a conformational change. ... Ubiquinone Coenzyme Q10 (also known as ubiquinone, ubidecarenone, or CoQ10) is a benzoquinone, where the Q and the 10 in the name refer to the quinone chemical group and the 10 isoprenyl chemical subunits, respectively. ...

Succinate-Q oxidoreductase (complex II)

Complex II: Succinate-Q oxidoreductase.

Succinate-Q oxidoreductase, also known as complex II or succinate dehydrogenase, is a second entry point to the electron transport chain.^[21] It is unusual because it is the only enzyme that is part of both the citric acid cycle and the electron transport chain. Complex II consists of four protein subunits and contains a bound flavin adenine dinucleotide (FAD) cofactor, iron–sulfur clusters, and a heme group that does not participate in electron transfer to coenzyme Q, but is believed to be important in decreasing production of reactive oxygen species.^[22][23] It oxidizes succinate to fumarate and reduces ubiquinone. As this reaction releases less energy than the oxidation of NADH, complex II does not transport protons across the membrane and does not contribute to the proton gradient. Image File history File links Complex_II.svg‎ File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Complex_II.svg‎ File historyClick on a date/time to view the file as it appeared at that time. ... Succinate—coenzyme Q reductase (EC 1. ... Succinate—coenzyme Q reductase (EC 1. ... For other uses, see FAD (disambiguation). ... Structure of Heme b A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. ... Succinic acid, originally called spirit of amber, is a carboxylic acid with the formula: HOOC-CH2-CH2-COOH At room temperature, pure succinic acid is a solid that forms colorless, odorless prisms. ... Fumaric acid (IUPAC systematic name: 2-butenedioic acid), also called allomaleic acid, boletic acid or lichenic acid, is a colorless crystalline flammable carboxylic acid based on butene and molecular formula C4H4O4. ...

In some eukaryotes, such as the parasitic worm Ascaris suum, an enzyme similar to complex II, fumarate reductase (menaquinol:fumarate oxidoreductase, or QFR) operates in reverse to oxidize ubiquinol and reduce fumarate. This allows the worm to survive in the anaerobic environment of the large intestine, carrying out anaerobic oxidative phosphorylation with fumarate as the electron acceptor.^[24] Another unconventional function of complex II is seen in the malaria parasite Plasmodium falciparum. Here, the reversed action of complex II as an oxidase is important in regenerating ubiquinol, which the parasite uses in an unusual form of pyrimidine biosynthesis.^[25] See also Parasitic worm (disambiguation) Parasitic worms or helminths are a division of eukaroytic parasites that, unlike external parasites such as lice and fleas, live inside their host. ... Binomial name Ascaris suum (Goeze, 1782) Ascaris suum is a parasitic nematode that causes Ascariasis in pigs. ... The large intestine is the last part of the digestive system: the final stage of the alimentary canal in vertebrate animals. ... Malaria is a vector-borne infectious disease caused by protozoan parasites. ... Binomial name Welch, 1897 Plasmodium falciparum is a protozoan parasite, one of the species of Plasmodium that cause malaria in humans. ... Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring [1]. It is isomeric with two other forms of diazine. ...

Electron transfer flavoprotein-Q oxidoreductase

Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-Q oxidoreductase), also known as electron transferring-flavoprotein dehydrogenase, is a third entry point to the electron transport chain. It is an enzyme that accepts electrons from electron-transferring flavoprotein in the mitochondrial matrix, and uses these electrons to reduce ubiquinone.^[26] This enzyme contains a flavin and a [4Fe–4S] cluster, but unlike the other respiratory complexes, it attaches to the surface of the membrane and does not cross the lipid bilayer.^[27] Electron-transferring-flavoprotein dehydrogenase (ETF dehydrogenase or electron transfer flavoprotein-ubiquinone oxidoreductase, EC 1. ... Electron transfer flavoproteins (ETFs) serve as specific electron acceptors for primary dehydrogenases, transferring the electrons to terminal respiratory systems such as electron-transferring-flavoprotein dehydrogenase. ... Riboflavin Flavin is a vaginal ring whose biochemical smell is pungent. ...

In mammals, this metabolic pathway is important in beta oxidation of fatty acids and catabolism of amino acids and choline, as it accepts electrons from multiple acetyl-CoA dehydrogenases.^[28][29] In plants, ETF-Q oxidoreductase is also important in the metabolic responses that allow survival in extended periods of darkness.^[30] Schematic demonstrating mitochondrial fatty acid beta-oxidation and effects of LCHAD deficiency Beta oxidation is the process by which fatty acids, in the form of Acyl-CoA molecules, are broken down in the mitochondria and/or in peroxisomes to generate Acetyl-CoA, the entry molecule for the Krebs Cycle. ... Not to be confused with fats. ... This article is about the class of chemicals. ... Choline is an organic compound, classified as an essential nutrient and usually grouped within the Vitamin B complex. ... Categories: Biochemistry stubs | Thiols ...

Q-cytochrome c oxidoreductase (complex III)

The two electron transfer steps in complex III: Q-cytochrome c oxidoreductase. After each step, Q (in the upper part of the figure) leaves the enzyme.

Q-cytochrome c oxidoreductase is also known as cytochrome c reductase, cytochrome bc₁ complex, or simply complex III.^[31][32] In mammals, this enzyme is a dimer, with each subunit complex containing 11 protein subunits, an [2Fe-2S] iron–sulfur cluster and three cytochromes; one cytochrome c₁ and two b cytochromes.^[33] A cytochrome is a kind of electron-transferring protein that contains at least one heme group. The iron atoms inside complex III’s heme groups alternate between a reduced ferrous (+2) and oxidized ferric (+3) state as the electrons are transferred through the protein. Image File history File links Size of this preview: 800 × 419 pixelsFull resolution (1872 × 981 pixels, file size: 212 KB, MIME type: image/png) Modified version of Image:Complex III reaction. ... Image File history File links Size of this preview: 800 × 419 pixelsFull resolution (1872 × 981 pixels, file size: 212 KB, MIME type: image/png) Modified version of Image:Complex III reaction. ... CoQ Cytochrome c reductase The Coenzyme Q - cytochrome c reductase complex, sometimes called the cytochrome bc1 complex, and at other times Complex III, is the third complex in the electron transfer chain (PDB 1KYO, EC 1. ... CoQ Cytochrome c reductase The Coenzyme Q - cytochrome c reductase complex, sometimes called the cytochrome bc1 complex, and at other times Complex III, is the third complex in the electron transfer chain (PDB 1KYO, EC 1. ... Sucrose, or common table sugar, is composed of glucose and fructose. ... Cytochromes are generally membrane-bound proteins that contain heme groups and carry out electron transport or catalyse reductive/oxidative reactions. ... Cytochromes are generally membrane-bound proteins that contain heme groups and carry out electron transport or catalyse reductive/oxidative reactions. ... Cytochromes are generally membrane-bound proteins that contain heme groups and carry out electron transport. ... Structure of Heme b A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. ...

The reaction catalyzed by complex III is the oxidation of one molecule of ubiquinol and the reduction of two molecules of cytochrome c, a heme protein loosely associated with the mitochondrion. Unlike coenzyme Q, which carries two electrons, cytochrome c carries only one electron. Ubiquinone Coenzyme Q10 (also known as ubiquinone, ubidecarenone, or CoQ10) is a benzoquinone, where the Q and the 10 in the name refer to the quinone chemical group and the 10 isoprenyl chemical subunits, respectively. ... Cytochrome c with heme c. ...

As only one of the electrons can be transferred from the QH₂ donor to a cytochrome c acceptor at a time, the reaction mechanism of complex III is more elaborate than those of the other respiratory complexes, and occurs in two steps called the Q cycle.^[34] In the first step, the enzyme binds three substrates, first, QH₂, which is then oxidized, with one electron being passed to the second substrate, cytochrome c. The two protons released from QH₂ pass into the intermembrane space. The third substrate is Q, which accepts the second electron from the QH₂ and is reduced to Q^.-, which is the ubisemiquinone free radical. The first two substrates are released, but this ubisemiquinone intermediate remains bound. In the second step, a second molecule of QH₂ is bound and again passes its first electron to a cytochrome c acceptor. The second electron is passed to the bound ubisemiquinone, reducing it to QH₂ as it gains two protons from the mitochondrial matrix. This QH₂ is then released from the enzyme.^[35] A semiquinone is a free radical resulting from the removal of one hydrogen atom with its electron during the process of dehydrogenation of a hydroquinone to quinone or alternatively the addition of a single H atom to a quinone. ... In chemistry free radicals are uncharged atomic or molecular species with unpaired electrons or an otherwise open shell configuration. ...

As coenzyme Q is reduced to ubiquinol on the inner side of the membrane and oxidized to ubiquinone on the other, this causes the net transfer of protons across the membrane, adding to the proton gradient.^[3] The rather complex two-step mechanism by which this occurs is important as it increases the efficiency of proton transfer. If instead of the Q cycle, one molecule of QH₂ was used to directly reduce two molecules of cytochrome c, the efficiency would be halved, with only one proton transferred per cytochrome c reduced.^[3]

Cytochrome c oxidase (complex IV)

For more details on this topic, see cytochrome c oxidase.

Complex IV: cytochrome c oxidase.

Cytochrome c oxidase, also known as complex IV, is the final protein complex in the electron transport chain.^[36] The mammalian enzyme has an extremely complex structure and contains 13 subunits, two heme groups, as well as multiple metal ion cofactors – in all three atoms of copper, one of magnesium and one of zinc.^[37] Cytochrome c oxidase The enzyme cytochrome c oxidase (PDB 2OCC, EC 1. ... Image File history File links Complex_IV.svg‎ File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Complex_IV.svg‎ File historyClick on a date/time to view the file as it appeared at that time. ... Cytochrome c oxidase The enzyme cytochrome c oxidase (PDB 2OCC, EC 1. ... Cytochrome c oxidase The enzyme cytochrome c oxidase (PDB 2OCC, EC 1. ... For other uses, see Copper (disambiguation). ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ...

This enzyme mediates the final reaction in the electron transport chain and transfers electrons to oxygen, while pumping protons across the membrane.^[38] The final electron acceptor oxygen, which is also called the terminal electron acceptor, is reduced to water in this step. Both the direct pumping of protons and the consumption of matrix protons in the reduction of oxygen contribute to the proton gradient. The reaction catalyzed is the oxidation of cytochrome c and the reduction of oxygen: An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. ...

Alternative reductases and oxidases

Many eukaryotic organisms have electron transport chains that differ from the well-studied mammalian enzymes described above. For example, in plants, alternative NADH oxidases exist that oxidize NADH in the cytosol, rather than the mitochondrial matrix, and pass these electrons to the ubiquinone pool.^[39] These enzymes do not transport protons and therefore reduce ubiquinone without altering the electrochemical gradient across the inner membrane.^[40] For other uses, see Plant (disambiguation). ...

Another example of a divergent electron transport chain is the alternative oxidase, which is found in plants, as well as some fungi, protists, and possibly some animals.^[41][42] This enzyme transfers electrons directly from ubiquinol to oxygen.^[43] The alternative oxidase shown as part of the complete electron transport chain. ... For other uses, see Plant (disambiguation). ... For the fictional character, see Fungus the Bogeyman. ... Typical phyla Chromalveolata Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Cabozoa Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: (RP); (GenAm)), Greek protiston -a meaning the (most) first of all...

The electron transport pathways produced by these alternative NADH and ubiquinone oxidases have lower ATP yields than the full pathway. The advantages produced by a shortened pathway are not entirely clear. However, the alternative oxidase is produced in response to stresses such as cold, reactive oxygen species and infection by pathogens, as well as other factors that inhibit the full electron transport chain.^[44][45] Alternative pathways might therefore enhance an organisms' resistance to injury, by reducing oxidative stress.^[46] Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... Reactive oxygen species (ROS) include oxygen ions, free radicals and peroxides both inorganic and organic. ... Oxidative stress is caused by an imbalance between the production of reactive oxygen and a biological systems ability to readily detoxify the reactive intermediates or easily repair the resulting damage. ...

Organization of complexes

The original model for how the respiratory chain complexes are organized was that they diffuse freely and independently in the mitochondrial membrane.^[16] However, recent data suggest that the complexes might form higher-order structures called supercomplexes or "respirasomes."^[47] In this model, the various complexes exist as organized sets of interacting enzymes.^[48] These associations might allow channeling of substrates between the various enzyme complexes, increasing the rate and efficiency of electron transfer.^[49] Within such mammalian supercomplexes, some components would be present in higher amounts than others, with a ratio between complexes I/II/III/IV and the ATP synthase of approximately 1:1:3:7:4.^[50] However, the debate over this supercomplex model is not completely resolved, as some data do not appear to fit with this model.^[16][51]

Prokaryotic electron transport chains

Further information: Microbial metabolism

In contrast to the general similarity in structure and function of the electron transport chains in eukaryotes, bacteria and archaea possess a large variety of electron-transfer enzymes. These use an equally wide set of chemicals as substrates.^[52] In common with eukaryotes, prokaryotic electron transport uses the energy released from the oxidation of a substrate to pump ions across a membrane and generate an electrochemical gradient. In the bacteria, oxidative phosphorylation in Escherichia coli is understood in most detail, while archaeal systems are at present poorly-understood.^[53] Microbial metabolism is the means by which a microbe obtains the energy and nutrients (e. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota ARMAN The Archaea (pronounced ) are a group of prokaryotic and single-celled microorganisms. ... E. coli redirects here. ...

The main difference between eukaryotic and prokaryotic oxidative phosphorylation is that bacteria and archaea use many different substances to donate or accept electrons. This allows prokaryotes to grow under a wide variety of environmental conditions.^[54] In E. coli, for example, oxidative phosphorylation can be driven by a large number of pairs of reducing agents and oxidizing agents, which are listed below. The midpoint potential of a chemical measures how much energy is released when it is oxidized or reduced, with reducing agents having negative potentials and oxidizing agents positive potentials. It has been suggested that Electrode potential be merged into this article or section. ...

As shown above, E. coli can grow with reducing agents such as formate, hydrogen or lactate as electron donors, and nitrate, DMSO or oxygen as acceptors.^[54] The larger the difference in midpoint potential between an oxidizing and reducing agent, the more energy is released when they react. Out of these compounds, the succinate/fumarate pair is unusual, as its midpoint potential is close to zero. Succinate can therefore be oxidized to fumarate if a strong oxidizing agent such as oxygen is available, or fumarate can be reduced to succinate using a strong reducing agent such as formate. These alternative reactions are catalyzed by succinate dehydrogenase and fumarate reductase, respectively.^[56] Formate dehydrogenases are a set of enzymes that catalyse the oxidation of formate to bicarbonate, donating the electrons to a second substrate, such as NAD+ in formate:NAD+ oxidoreductase (EC 1. ... For baking soda, see Sodium bicarbonate In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. ... Formate or methanoate is the ion is HCOO- (formic acid minus one hydrogen ion). ... A hydrogenase is an enzyme that catalyses the reversible oxidation of molecular hydrogen (H2). ... For other uses, see Proton (disambiguation). ... This article is about the chemistry of hydrogen. ... NADH dehydrogenase NADH dehydrogenase (EC 1. ... Nicotinamide adenine dinucleotide (NAD+ or in older notation DPN+) is an important coenzyme found in cells. ... Nicotinamide adenine dinucleotide (NAD+ or in older notation DPN+) is an important coenzyme found in cells. ... Glycerol-3-phosphate dehydrogenase converts glycerol 3-phosphate to dihydroxyacetone phosphate. ... DHAP (or Dihydroxyacetonephosphate) is a biochemical compound involved in many reactions, from the Calvin Cycle in plants to the ether-lipid biosynthesis process in Leishmania mexicana. ... Dehydrogenation of L-Glycerol 3-phosphate produces DHAP and is part of the entry of glycerol (sourced from triglycerides) into the glycolytic pathway. ... Pyruvate dehydrogenase is an enzyme (E1) in the pyruvate dehydrogenase complex (PDC). ... R-phrases , S-phrases , , , Flash point 43 °C Related Compounds Related carboxylic; acids Formic acid; Propionic acid; Butyric acid Related compounds acetamide; ethyl acetate; acetyl chloride; acetic anhydride; acetonitrile; acetaldehyde; ethanol; thioacetic acid; acetylcholine; acetylcholinesterase Supplementary data page Structure and properties n, εr, etc. ... Carbon dioxide (chemical formula: ) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Pyruvic acid (CH3COCO2H) is an alpha-keto acid which plays an important role in biochemical processes. ... Lactate dehydrogenase (LDH) is an enzyme (EC 1. ... Pyruvic acid (CH3COCO2H) is an alpha-keto acid which plays an important role in biochemical processes. ... For the production of milk by mammals, see Lactation. ... D-amino-acid dehydrogenase (EC 1. ... An oxoacid is an acid which contains oxygen. ... For other uses, see Ammonia (disambiguation). ... This article is about the class of chemicals. ... Gluconic acid is the carboxylic acid formed by the oxidation of the first carbon of glucose and has the chemical formula C6H12O7. ... Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ... Succinate—coenzyme Q reductase (EC 1. ... Fumaric acid (IUPAC systematic name: 2-butenedioic acid), also called allomaleic acid, boletic acid or lichenic acid, is a colorless crystalline flammable carboxylic acid based on butene and molecular formula C4H4O4. ... Succinic acid, originally called spirit of amber, is a carboxylic acid with the formula: HOOC-CH2-CH2-COOH At room temperature, pure succinic acid is a solid that forms colorless, odorless prisms. ... Ubiquinol oxidases (EC 1. ... This article is about the chemical element and its most stable form, or dioxygen. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Nitrate reducatse are group of enzymes which reduce nitrate to nitrite This article belongs in one or more categories. ... Trinitrate redirects here. ... // Definition The nitrite ion is NO2−. A nitrite compound is one that contains this group, either an ionic compound, or an analogous covalent one. ... Nitrite reductase refers to any of several classes of enyzmes that catalyze the reduction of nitrite. ... // Definition The nitrite ion is NO2−. A nitrite compound is one that contains this group, either an ionic compound, or an analogous covalent one. ... For other uses, see Ammonia (disambiguation). ... DMSO reductase is a molybdenum-containing enzyme capable of reducing dimethyl sulfoxide (DMSO) to dimethyl sulfide (DMS). ... Dimethyl sulfoxide (DMSO) is the chemical compound with the formula (CH3)2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water. ... Dimethyl sulfide causes that distinctive smell from your St. ... Trimethylamine N-oxide reductase (TOR or TMAO reductase, EC 1. ... Trimethylamine N-oxide (TMAO or TMANO) is a naturally occurring osmolyte that occurs in saltwater fish, sharks and rays, molluscs, and crustaceans. ... Trimethylamine, also known as NMe3, N(CH3)3, and TMA, is a colorless, hygroscopic, and flammable simple amine with a typical fishy odor in low concentrations and an ammonia-like odor in higher concentrations. ... Fumarate reductase is the enzyme that converts fumarate to succinate, it is important in microbial metabolism as a means for anaerobic respiration. ... Fumaric acid (IUPAC systematic name: 2-butenedioic acid), also called allomaleic acid, boletic acid or lichenic acid, is a colorless crystalline flammable carboxylic acid based on butene and molecular formula C4H4O4. ... Succinic acid, originally called spirit of amber, is a carboxylic acid with the formula: HOOC-CH2-CH2-COOH At room temperature, pure succinic acid is a solid that forms colorless, odorless prisms. ... Succinate—coenzyme Q reductase (EC 1. ... Fumarate reductase is the enzyme that converts fumarate to succinate, it is important in microbial metabolism as a means for anaerobic respiration. ...

Some prokaryotes use redox pairs that have only a small difference in midpoint potential. For example, nitrifying bacteria such as Nitrobacter oxidize nitrite to nitrate, donating the electrons to oxygen. The small amount of energy released in this reaction is enough to pump protons and generate ATP, but not enough to produce NADH or NADPH directly for use in anabolism.^[57] This problem is solved by using a nitrite oxidoreductase to produce enough proton-motive force to run part of the electron transport chain in reverse, causing complex I to generate NADH.^[58][59] Nitrogen cycle Nitrification is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitrites into nitrates. ... Nitrobacter is a rod-shaped bacteria, which is an important part of the nitrogen cycle. ... Anabolism is the metabolic process that builds larger molecules from smaller ones. ... Nitrite oxidoreductase (NOR or NXR) is an enzyme involved in nitrification. ...

Prokaryotes control their use of these electron donors and acceptors by varying which enzymes are produced, in response to environmental conditions.^[60] This flexibility is possible because different oxidases and reductases use the same ubiquinone pool. This allows many combinations of enzymes to function together, linked by the common ubiquinol intermediate.^[55] These respiratory chains therefore have a modular design, with easily interchangeable sets of enzyme systems. The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...

In addition to this metabolic diversity, prokaryotes also possess a range of isozymes – different enzymes that catalyze the same reaction. For example, in E. coli there are two different types of ubiquinol oxidase using oxygen as an electron acceptor. Under highly-aerobic conditions, the cell uses an oxidase with a low affinity for oxygen that can transport two protons per electron. However, if levels of oxygen fall, they switch to an oxidase that only transfers one proton per electron, but has a high affinity for oxygen.^[61] Isozymes, (or isoenzymes) are isoforms (closely related variants) of enzymes. ...

ATP synthase

Further information: ATP synthase

ATP synthase. The F_O proton channel and stalk are shown in blue, the F₁ synthase domain in red and the membrane in gray.

ATP synthase, also called complex V, is the final enzyme in the oxidative phosphorylation pathway. This enzyme is found in all forms of life and functions in the same way in both prokaryotes and eukaryotes.^[62] The enzyme uses the energy stored in a proton gradient across a membrane to drive the synthesis of ATP from ADP and phosphate (P_i). Estimates of the number of protons required to synthesise one ATP have ranged from three to four,^[63][64] with some suggesting cells can vary this ratio, to suit different conditions.^[65] An ATP synthase (EC 3. ... Image File history File links Size of this preview: 431 × 599 pixelsFull resolution (461 × 641 pixel, file size: 278 KB, MIME type: image/png) Modified version of December 2005 PDB Molecule of the Month by David S. Goodsell link File historyClick on a date/time to view the file as... Image File history File links Size of this preview: 431 × 599 pixelsFull resolution (461 × 641 pixel, file size: 278 KB, MIME type: image/png) Modified version of December 2005 PDB Molecule of the Month by David S. Goodsell link File historyClick on a date/time to view the file as... An ATP synthase (EC 3. ... A phosphate, in inorganic chemistry, is a salt of phosphoric acid. ...

This phosphorylation reaction is an equilibrium, which can be shifted by altering the proton-motive force. In the absence of a proton-motive force, the ATP synthase reaction will run from right to left, hydrolyzing ATP and pumping protons out of the matrix across the membrane. However, when the proton-motive force is high, the reaction is forced to run in the opposite direction; it proceeds from left to right, allowing protons to flow down their concentration gradient and turning ADP into ATP.^[62] Indeed, in the closely related vacuolar type H+-ATPases the same reaction is used to acidify cellular compartments, by pumping protons and hydrolysing ATP.^[66] A phosphorylated serine residue Phosphorylation is the addition of a phosphate (PO4) group to a protein molecule or a small molecule. ... A burette, an apparatus for carrying out acid-base titration, is