query: what are the final electron acceptors for the electron transport chains in light reactions

pos: Light-dependent reactions the green color of leaves. The light-dependent reactions begin in photosystem II. When a chlorophyll "a" molecule within the reaction center of PSII absorbs a photon, an electron in this molecule attains a higher energy level. Because this state of an electron is very unstable, the electron is transferred from one to another molecule creating a chain of redox reactions, called an electron transport chain (ETC). The electron flow goes from PSII to cytochrome b6f to PSI. In PSI, the electron gets the energy from another photon. The final electron acceptor is NADP. In oxygenic photosynthesis, the first electron donor

pos: Electron transport chain their cell membrane. In chloroplasts, light drives the conversion of water to oxygen and NADP to NADPH with transfer of H ions across chloroplast membranes. In mitochondria, it is the conversion of oxygen to water, NADH to NAD and succinate to fumarate that are required to generate the proton gradient. Electron transport chains are major sites of premature electron leakage to oxygen, generating superoxide and potentially resulting in increased oxidative stress. The electron transport chain consists of a spatially separated series of redox reactions in which electrons are transferred from a donor molecule to an acceptor molecule. The underlying force

pos: Light-dependent reactions the green color of leaves. The light-dependent reactions begin in photosystem II. When a chlorophyll "a" molecule within the reaction center of PSII absorbs a photon, an electron in this molecule attains a higher energy level. Because this state of an electron is very unstable, the electron is transferred from one to another molecule creating a chain of redox reactions, called an electron transport chain (ETC). The electron flow goes from PSII to cytochrome b6f to PSI. In PSI, the electron gets the energy from another photon. The final electron acceptor is NADP. In oxygenic photosynthesis, the first electron donor

pos: Hill reaction which oxygen is released takes place within the chloroplast of plants and the Hill reaction demonstrated that the release of oxygen (O) is only a partial reaction which requires one step of photosynthesis. The Hill reaction implies that the light dependent reaction of photosynthesis is a result of a series of redox reactions and a suitable terminal electron acceptor is required for that reaction to occur. Plants have natural electron acceptors such as NADP, that play a major role in the oxidation of water. The Hill reaction also shows that the natural electron acceptors of the reaction can be substituted

pos: Chloroplast in position to be used in the dark reactions. Electrons are often removed from the electron transport chains to charge NADP with electrons, reducing it to NADPH. Like ATP synthase, ferredoxin-NADP reductase, the enzyme that reduces NADP, releases the NADPH it makes into the stroma, right where it is needed for the dark reactions. Because NADP reduction removes electrons from the electron transport chains, they must be replaced—the job of photosystem II, which splits water molecules (HO) to obtain the electrons from its hydrogen atoms. While photosystem II photolyzes water to obtain and energize new electrons, photosystem I simply reenergizes

pos: Chloroplast depleted electrons at the end of an electron transport chain. Normally, the reenergized electrons are taken by NADP, though sometimes they can flow back down more H-pumping electron transport chains to transport more hydrogen ions into the thylakoid space to generate more ATP. This is termed cyclic photophosphorylation because the electrons are recycled. Cyclic photophosphorylation is common in plants, which need more ATP than NADPH. The Calvin cycle, also known as the dark reactions, is a series of biochemical reactions that fixes CO into G3P sugar molecules and uses the energy and electrons from the ATP and NADPH made in

pos: Dehydrogenase oxidases typically transfer the equivalent of dihydrogen (H), and the acceptor is a dioxygen. Similarly, a peroxidase (another subclass of oxidoreductases) will use a peroxide (HO) as the electron acceptor, rather than an oxygen. Dehydrogenase enzymes transfer electrons from the substrate to an electron carrier; what carrier is used depends on the reaction taking place. Common electron acceptors used by this subclass are NAD, FAD, and NADP. Electron carriers are reduced in this process and considered oxidizers of the substrate. Electron carriers are coenzymes that are often referred to as "redox cofactors." NAD, or nicotinamide adenine dinucleotide, is a dinucleotide,

pos: Transduction (biophysics) [This is quite wrong: NADP is reduced (electrons are added) to NADPH in the light reactions of linear electron transport. No ATP involved directly. Phosphate is "linked" to ADP, forming ATP, but this does not involve NADP(H), it involves the proton gradient (and ATP synthase) generated by photosynthetic electron transport processes.] This means that the photon's energy ends up its circuit by being "transduced" to an electron that takes part in the formation of a molecular link of energy-rich phosphate. In the pathway of this end-point transduction, the energy is "transferred" along a number of molecules (cytochromes), in a downward

neg: Light-dependent reactions process in chloroplasts begins when an electron of P680 of PSII attains a higher-energy level. This energy is used to reduce a chain of electron acceptors that have subsequently lowered redox-potentials. This chain of electron acceptors is known as an electron transport chain. When this chain reaches PS I, an electron is again excited, creating a high redox-potential. The electron transport chain of photosynthesis is often put in a diagram called the z-scheme, because the redox diagram from P680 to P700 resembles the letter z. The final product of PSII is plastoquinol, a mobile electron carrier in the membrane. Plastoquinol

neg: Oxidative phosphorylation ATP. In eukaryotes, these redox reactions are carried out by a series of protein complexes within the inner membrane of the cell's mitochondria, whereas, in prokaryotes, these proteins are located in the cells' intermembrane space. These linked sets of proteins 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. The energy released by electrons flowing through this electron transport chain is used to transport protons across the inner mitochondrial membrane, in a process called "electron transport". This generates potential energy

neg: Electron transport chain aerobic respiration is molecular oxygen although a variety of acceptors other than oxygen such as sulfate exist in anaerobic respiration. Electron transport chains are used for extracting energy via redox reactions from sunlight in photosynthesis or, such as in the case of the oxidation of sugars, cellular respiration. In eukaryotes, an important electron transport chain is found in the inner mitochondrial membrane where it serves as the site of oxidative phosphorylation through the action of ATP synthase. It is also found in the thylakoid membrane of the chloroplast in photosynthetic eukaryotes. In bacteria, the electron transport chain is located in

neg: Electron transport chain powers most cellular reactions. A small amount of ATP is available from substrate-level phosphorylation, for example, in glycolysis. In most organisms the majority of ATP is generated in electron transport chains, while only some obtain ATP by fermentation. Most eukaryotic cells have mitochondria, which produce ATP from products of the citric acid cycle, fatty acid oxidation, and amino acid oxidation. At the mitochondrial inner membrane, electrons from NADH and FADH2 pass through the electron transport chain to oxygen, which is reduced to water. The electron transport chain comprises an enzymatic series of electron donors and acceptors. Each electron donor will

neg: Electron transport chain to the acceptor through another electron transport chain. Photosynthetic electron transport chains have many similarities to the oxidative chains discussed above. They use mobile, lipid-soluble carriers (quinones) and mobile, water-soluble carriers (cytochromes, etc.). They also contain a proton pump. It is remarkable that the proton pump in "all" photosynthetic chains resembles mitochondrial "Complex III". Photosynthetic electron transport chains are discussed in greater detail in the articles Photophosphorylation, Photosynthesis, Photosynthetic reaction center and Light-dependent reaction. Electron transport chains are redox reactions that transfer electrons from an electron donor to an electron acceptor. The transfer of electrons is coupled to the translocation

neg: Electron transport chain Electron transport chain An electron transport chain (ETC) is a series of complexes that transfer electrons from electron donors to electron acceptors via redox (both reduction and oxidation occurring simultaneously) reactions, and couples this electron transfer with the transfer of protons (H ions) across a membrane. This creates an electrochemical proton gradient that drives the synthesis of adenosine triphosphate (ATP), a molecule that stores energy chemically in the form of highly strained bonds. The molecules of the chain include peptides, enzymes (which are proteins or protein complexes), and others. The final acceptor of electrons in the electron transport chain during

neg: Electron transport chain Acceptor". Individual bacteria use multiple electron transport chains, often simultaneously. Bacteria can use a number of different electron donors, a number of different dehydrogenases, a number of different oxidases and reductases, and a number of different electron acceptors. For example, "E. coli" (when growing aerobically using glucose as an energy source) uses two different NADH dehydrogenases and two different quinol oxidases, for a total of four different electron transport chains operating simultaneously. A common feature of all electron transport chains is the presence of a proton pump to create a transmembrane proton gradient. Bacterial electron transport chains may contain as

neg: Anaerobic respiration Anaerobic respiration Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain. In aerobic organisms undergoing respiration, electrons are shuttled to an electron transport chain, and the final electron acceptor is oxygen. Molecular oxygen is a highly oxidizing agent and, therefore, is an excellent electron acceptor. In anaerobes, other less-oxidizing substances such as sulfate (SO), nitrate (NO), sulphur (S), or fumarate are used. These terminal electron acceptors have smaller reduction potentials than O, meaning that less energy is released per oxidized

neg: Electron transport chain and inorganic. If oxygen is available, it is invariably used as the terminal electron acceptor, because it generates the greatest Gibbs free energy change and produces the most energy. In anaerobic environments, different electron acceptors are used, including nitrate, nitrite, ferric iron, sulfate, carbon dioxide, and small organic molecules such as fumarate. Since electron transport chains are redox processes, they can be described as the sum of two redox pairs. For example, the mitochondrial electron transport chain can be described as the sum of the NAD/NADH redox pair and the O/HO redox pair. NADH is the electron donor and O

neg: Electron transport chain of protons across a membrane, producing a proton gradient. The proton gradient is used to produce useful work. About 30 work units are produced per electron transport. Electron transport chain An electron transport chain (ETC) is a series of complexes that transfer electrons from electron donors to electron acceptors via redox (both reduction and oxidation occurring simultaneously) reactions, and couples this electron transfer with the transfer of protons (H ions) across a membrane. This creates an electrochemical proton gradient that drives the synthesis of adenosine triphosphate (ATP), a molecule that stores energy chemically in the form of highly strained bonds.

neg: Anaerobic respiration anaerobic respiration. Anaerobic respiration is useful in generating electricity in microbial fuel cells, which employ bacteria that respire solid electron acceptors (such as oxidized iron) to transfer electrons from reduced compounds to an electrode. This process can simultaneously degrade organic carbon waste and generate electricity. Anaerobic respiration Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain. In aerobic organisms undergoing respiration, electrons are shuttled to an electron transport chain, and the final electron acceptor is oxygen. Molecular oxygen is a

neg: Oxidizing agent organic redox reactions involve atom-transfer reactions. Electron acceptors participate in electron-transfer reactions. In this context, the oxidizing agent is called an electron acceptor and the reducing agent is called an electron donor. A classic oxidizing agent is the ferrocenium ion , which accepts an electron to form Fe(CH). One of the strongest acceptors commercially available is "Magic blue", the radical cation derived from N(CH-4-Br). Extensive tabulations of ranking the electron accepting properties of various reagents (redox potentials) are available, see Standard electrode potential (data page). In more common usage, an oxidising agent transfers oxygen atoms to a substrate. In this

neg: Thylakoid are the site of the light-dependent reactions of photosynthesis. These include light-driven water oxidation and oxygen evolution, the pumping of protons across the thylakoid membranes coupled with the electron transport chain of the photosystems and cytochrome complex, and ATP synthesis by the ATP synthase utilizing the generated proton gradient. The first step in photosynthesis is the light-driven reduction (splitting) of water to provide the electrons for the photosynthetic electron transport chains as well as protons for the establishment of a proton gradient. The water-splitting reaction occurs on the lumenal side of the thylakoid membrane and is driven by the light

neg: Hill reaction this haem group undergoes redox reactions: Fe + e → Fe Fe + e ← Fe Robin Hill (1937) studied the redox reactions in photosynthesis using "artificial" electron acceptors. He studied the reaction with the absence of CO by placing isolated active chloroplasts under light and dark conditions. During his observations of isolated chloroplasts placed under light conditions but with the absence of CO, the artificial electron acceptors were reduced and then oxidized, completing the cycle and allowing the process to proceed. Oxygen (O) was released as a byproduct, but there was no production of a sugar (CHO) under those

neg: Cellular respiration However some anaerobic organisms, such as methanogens are able to continue with anaerobic respiration, yielding more ATP by using other inorganic molecules (not oxygen) as final electron acceptors in the electron transport chain. They share the initial pathway of glycolysis but aerobic metabolism continues with the Krebs cycle and oxidative phosphorylation. The post-glycolytic reactions take place in the mitochondria in eukaryotic cells, and in the cytoplasm in prokaryotic cells. 1. Glycolysis: --- "2 ATPs + Glucose → 2 Pyruvic Acid + 4 Hydrogen + 4 ATPs" 2. Formation of Acetyl CoA: --- "2 Pyruvic Acid + 2 CoA → 2

neg: Quinone of quinones is for the production of hydrogen peroxide. 2-Alkylanthraquinones are hydrogenated to the corresponding hydroquinones (quinizarins), which then transfer to oxygen: In this way, several billion kilograms of are produced annually. Derivatives of quinones are common in biologically active molecules. Some serve as electron acceptors in electron transport chains such as those in photosynthesis (plastoquinone, phylloquinone), and aerobic respiration (ubiquinone). Phylloquinone is also known as Vitamin K as it is used by animals to carboxylate certain proteins, which are involved in blood coagulation, bone formation, and other processes. Conversely, the toxicity of paracetamol is due to its metabolism to

neg: Electron transport chain can synthesize different transmembrane complexes and produce different electron transport chains in their cell membranes. Bacteria select their electron transport chains from a DNA library containing multiple possible dehydrogenases, terminal oxidases and terminal reductases. The situation is often summarized by saying that electron transport chains in bacteria are "branched", "modular", and "inducible". In oxidative phosphorylation, electrons are transferred from a low-energy electron donor (e.g., NADH) to an acceptor (e.g., O) through an electron transport chain. In photophosphorylation, the energy of sunlight is used to "create" a high-energy electron donor and an electron acceptor. Electrons are then transferred from the donor

neg: Methanogenesis using a nickel-containing protein similar to methyl-coenzyme M reductase used by methanogenic archaea. Reverse methanogenesis occurs according to the reaction: Methanogenesis is the final step in the decay of organic matter. During the decay process, electron acceptors (such as oxygen, ferric iron, sulfate, and nitrate) become depleted, while hydrogen (H) and carbon dioxide accumulate. Light organics produced by fermentation also accumulate. During advanced stages of organic decay, all electron acceptors become depleted except carbon dioxide. Carbon dioxide is a product of most catabolic processes, so it is not depleted like other potential electron acceptors. Only methanogenesis and fermentation can occur

neg: Photosynthesis electron-acceptor molecule, pheophytin. As the electrons are shuttled through an electron transport chain (the so-called Z-scheme shown in the diagram), it initially functions to generate a chemiosmotic potential by pumping proton cations (H) across the membrane and into the thylakoid space. An ATP synthase enzyme uses that chemiosmotic potential to make ATP during photophosphorylation, whereas NADPH is a product of the terminal redox reaction in the "Z-scheme". The electron enters a chlorophyll molecule in Photosystem I. There it is further excited by the light absorbed by that photosystem. The electron is then passed along a chain of electron acceptors to

neg: Electron transport chain reduce oxygen to water. Anaerobic bacteria, which do not use oxygen as a terminal electron acceptor, have terminal reductases individualized to their terminal acceptor. For example, "E. coli" can use fumarate reductase, nitrate reductase, nitrite reductase, DMSO reductase, or trimethylamine-N-oxide reductase, depending on the availability of these acceptors in the environment. Most terminal oxidases and reductases are "inducible". They are synthesized by the organism as needed, in response to specific environmental conditions. Just as there are a number of different electron donors (organic matter in organotrophs, inorganic matter in lithotrophs), there are a number of different electron acceptors, both organic

neg: Benznidazole create a reactive nitro radical species. The nitro radical can then either engage in other redox reactions directly or spontaneously give rise to a nitrite ion and imidazole radical instead. The initial reduction takes place because nitroimidazoles are better electron acceptors for ferredoxin than the natural substrates. In mammals, the principal mediators of electron transport are NAD+/NADH and NADP+/NADPH, which have a more positive reduction potential and so will not reduce nitroimidazoles to the radical form. This limits the spectrum of activity of nitroimidazoles so that host cells and DNA are not also damaged. This mechanism has been well-established for

neg: Oxidative phosphorylation for use in anabolism. 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. Prokaryotes control their use of these electron donors and acceptors by varying which enzymes are produced, in response to environmental conditions. 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. These respiratory chains therefore have a modular design, with easily interchangeable sets of enzyme systems. In

neg: MTRR (gene) Flavoprotein pyridine nucleotide cytochrome reductases, including FAD catalyse the interchange of reducing equivalents (H+ or electrons). Initial electron donors and final electron acceptors comprise single electron carriers and two electron carrying nicotinamide dinucleotides respectively. Evolutionary conserved protein domain corresponding to oxidoreductase activity. NAD binding catalyzes redox reactions to alter the oxidation state of metal ions, using NADP+ as an electron acceptor. Involved in the reductive remethylation of cob(II)alamin using S-adenosylhomocysteine as a methyl donor. Catalyses the reaction: [methionine synthase]- cob(II)alamin + NADPH + H+ + S-adenosylmethionine → [methionine synthase]-methylcob(I)alamin + S-adenosylhomocysteine + NADP+. Belongs to the oxidoreductase family, oxidizing metal

neg: Light-dependent reactions with astonishingly high efficiency. Electrons are removed from excited chlorophyll molecules and transferred through a series of intermediate carriers to "ferredoxin", a water-soluble electron carrier. As in PS II, this is a solid-state process that operates with 100% efficiency. There are two different pathways of electron transport in PS I. In "noncyclic electron transport", ferredoxin carries the electron to the enzyme ferredoxin reductase (FNR) that reduces to NADPH. In "cyclic electron transport", electrons from ferredoxin are transferred (via plastoquinone) to a proton pump, cytochrome ". They are then returned (via plastocyanin) to P700. NADPH and ATP are used to synthesize

neg: Contorted aromatics crystalline cables which act as p-type semiconductors. The contorted peripheral edges of these molecules serve to provide unique intermolecular contacts which make these molecules efficient in charge transport. The tetra-dodecaloxy side chains in c-HBC promotes the self-assembly. These materials are deposited in the form a columnar hexagonal liquid crystals. The main aromatic core transport the charges and side chains act as insulators. In thin film, the columns arrange themselves parallel to the surface and allows lateral charge transport. Influenced by fullerenes themselves, the following structural features are incorporated into the non-fullerene-based electron acceptors. Figure 9 A more recently devised Pd

neg: Photosynthetic reaction centre a chain of nearby electron acceptors, which have subsequently higher redox-potentials. These electron transfer steps are the initial phase of a series of energy conversion reactions, ultimately resulting in the conversion of the energy of photons to the storage of that energy by the production of chemical bonds. Reaction centers are present in all green plants, algae, and many bacteria. Although these species are separated by billions of years of evolution, the reaction centers are homologous for all photosynthetic species. In contrast, a large variety in light-harvesting complexes exist between the photosynthetic species. Green plants and algae have two different

neg: Hill reaction reduction. By the studies of light intensities, it is concluded that the effect is largely on the light-independent steps of the Hill reaction. These observations are explained in terms of a proposed method in which phosphate esterfies during electron transport reactions, leading to the reduction of ferricyanide, and the rate of electron transport is limited by the rate of phosphorylation. If there is an increase in the rate of phosphorylation, then there will be an increase in the rate by which electrons are transported in the electron transport system. It is possible to introduce into the light reaction an artificial

neg: Light-dependent reactions (hydrogen, hydrogen sulfide, sulfur, sulfite, or organic molecules such as succinate and lactate) to feed electrons into a reverse electron transport chain. Green sulfur bacteria contain a photosystem that is analogous to PS I in chloroplasts: There are two pathways of electron transfer. In "cyclic electron transfer", electrons are removed from an excited chlorophyll molecule, passed through an electron transport chain to a proton pump, and then returned to the chlorophyll. The mobile electron carriers are, as usual, a lipid-soluble quinone and a water-soluble cytochrome. The resulting proton gradient is used to make ATP. In "noncyclic electron transfer", electrons are

neg: Electron transport chain and archaea) the situation is more complicated, because there are several different electron donors and several different electron acceptors. The generalized electron transport chain in bacteria is: Note that electrons can enter the chain at three levels: at the level of a dehydrogenase, at the level of the quinone pool, or at the level of a mobile cytochrome electron carrier. These levels correspond to successively more positive redox potentials, or to successively decreased potential differences relative to the terminal electron acceptor. In other words, they correspond to successively smaller Gibbs free energy changes for the overall redox reaction "Donor →

neg: Electrochemical reaction mechanism Electrochemical reaction mechanism In chemistry, an electrochemical reaction mechanism is the step by step sequence of elementary steps, involving at least one outer sphere electron transfer, by which an overall chemical change occurs. Elementary steps like proton coupled electron transfer and the movement of electrons between an electrode and substrate are special to electrochemical processes. Electrochemical mechanisms are important to all redox chemistry including corrosion, redox active photochemistry including photosynthesis, other biological systems often involving electron transport chains and other forms of homogeneous and heterogeneous electron transfer. Such reactions are most often studied with standard three electrode techniques such as

neg: Light-dependent reactions the production of NADPH. Cyclic phosphorylation is important to create ATP and maintain NADPH in the right proportion for the light-independent reactions. The net-reaction of all light-dependent reactions in oxygenic photosynthesis is: The two photosystems are protein complexes that absorb photons and are able to use this energy to create an electron transport chain. Photosystem I and II are very similar in structure and function. They use special proteins, called light-harvesting complexes, to absorb the photons with very high effectiveness. If a special pigment molecule in a photosynthetic reaction center absorbs a photon, an electron in this pigment attains the

neg: Green sulfur bacteria PS I for photosynthesis. Thousands of bacteriochlorophyll(BCHl) c, d and e of the cells absorb light at 720-750 nm, and the light energy is transferred to BChl a-795 and a-808 before being transferred to Fenna-Matthews-Olson (FMO)-proteins which are connected to reaction centers (RC). The FMO complex then transfers the excitation energy to the RC with its special pair which absorbs at 840 nm in the plasma membrane. After the reaction centers receive the energy, electrons are ejected and transferred through electron transport chains (ETCs). Some electrons form Fe-S proteins in electron transport chains are accepted by ferredoxins (Fd) which can

neg: Photosynthetic reaction centre manner analogous to a ball falling down a staircase. In doing so, the electrons release energy. This is the process that is exploited by a photosynthetic reaction center. When an electron rises to a higher energy level, there is a corresponding decrease in the reduction potential of the molecule in which the electron resides occurs. This means that the molecule has a greater tendency to donate electrons, which is key to the conversion of light energy to chemical energy. In green plants, the electron transport chain has many electron acceptors including phaeophytin, quinone, plastoquinone, cytochrome bf, and ferredoxin, which result

neg: Stickland fermentation microbes can avoid using hydrogen ions as electron acceptors to produce hydrogen gas. Amino acids can be Stickland acceptors, Stickland donors, or act as both donor and acceptor. Only histidine cannot be fermented by Stickland reactions, and is oxidised. With a typical amino acid mix, there is a 10% shortfall in Stickland acceptors, which results in hydrogen production. Under very low hydrogen partial pressures, increased uncoupled anaerobic oxidation has also been observed. It occurs in proteolytic clostridiums such as: "C. perfringens", "C. difficile", "C. sporogenes", and "C. botulinum". Additionally, sarcosine and betaine can act as electron acceptors. Stickland fermentation Stickland

neg: Electron acceptor donor to an electron acceptor. During this process (electron transport chain) the electron acceptor is reduced and the electron donor is oxidized. Electron acceptor An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process. Electron acceptors are sometimes mistakenly called electron receptors. Typical oxidizing agents undergo permanent chemical alteration through covalent or ionic reaction chemistry, resulting in the complete and irreversible transfer of one or more electrons. In many chemical circumstances, however, the transfer of electronic

neg: Oxidative phosphorylation 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, which 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". 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

neg: Coordination sphere reactions. In associative ligand substitution, the entering nucleophile resides in the second coordination sphere. These effects are relevant to practical applications such as contrast agents used in MRI. The energetics of inner sphere electron transfer reactions are discussed in terms of second coordination sphere. Some proton coupled electron transfer reactions involve atom transfer between the second coordination spheres of the reactants: Solvent effects on colors and stability are often attributable to changes in the second coordination sphere. Such effects can be pronounced in complexes where the ligands in the first coordination sphere are strong hydrogen-bond donors and acceptors, e.g. respectively

neg: Dehydrogenase enzymes are dehydrogenases, although reductases are also common. The accepted nomenclature for dehydrogenases is "donor dehydrogenase," where the donor is the substrate that can be oxidized. Oxidation-reduction reactions are essential to growth and survival of organisms, as the oxidation of organic molecules produces energy. Energy-producing reactions can drive forward the synthesis of important energy molecules, such as ATP in glycolysis. For this reason, dehydrogenases have pivotal roles in metabolism. Dehydrogenases oxidize a substrate by transferring hydrogen to an electron acceptor, common electron acceptors being NAD or FAD. This would be considered an oxidation of the substrate, in which the substrate

neg: Adenosine triphosphate cytoplasm. Fermentation is the metabolism of organic compounds in the absence of air. It involves substrate-level phosphorylation in the absence of a respiratory electron transport chain. The equation for the oxidation of glucose to lactic acid is: Anaerobic respiration is respiration in the absence of . Prokaryotes can utilize a variety of electron acceptors. These include nitrate, sulfate, and carbon dioxide. ATP can also be synthesized through several so-called "replenishment" reactions catalyzed by the enzyme families of nucleoside diphosphate kinases (NDKs), which use other nucleoside triphosphates as a high-energy phosphate donor, and the family. In plants, ATP is synthesized in

neg: Plastoquinone Plastoquinone Plastoquinone (PQ) is an isoprenoid quinone molecule involved in the electron transport chain in the light-dependent reactions of photosynthesis. The most common form of plastoquinone, known as PQ-A or PQ-9, is a 2,3-dimethyl-1,4-benzoquinone molecule with a side chain of nine isoprenyl units. There are other forms of plastoquinone, such as ones with shorter side chains like PQ-3 (which has 3 isoprenyl side units instead of 9) as well as analogs such as PQ-B, PQ-C, and PQ-D, which differ in their side chains. The benzoquinone and isoprenyl units are both nonpolar, anchoring the molecule within the inner section of a

neg: Lithotroph few examples of chemolithotrophic pathways, any of which "may" use oxygen, sulfur or other molecules as electron acceptors: Photolithotrophs obtain energy from light and therefore use inorganic electron donors only to fuel biosynthetic reactions (e. g., carbon dioxide fixation in lithoautotrophs). Lithotrophic bacteria cannot use, of course, their inorganic energy source as a carbon source for the synthesis of their cells. They choose one of three options: In addition to this division, lithotrophs differ in the initial energy source which initiates ATP production: Lithotrophs participate in many geological processes, such as the formation of soil and the biogeochemical cycling of

neg: Polyfluorene the electron donating polymer’s highest occupied molecular orbital (HOMO) energy level and the electron accepting molecules lowest unoccupied molecular orbital (LUMO) energy level. By adding electron withdrawing pendant molecules to conjugated polymers, their HOMO energy level can be lowered. For instance by adding electronegative groups on the end of conjugated side chains, researchers lowered the HOMO of a polyfluorene copolymer to −5.30 eV and increased the voltage of a solar cell to 0.99 V. Typical polymer solar cells utilize fullerene molecules as electron acceptors because of their low LUMO energy level (high electron affinity). However the tunability of polyfluorenes allows

neg: Lithotroph the power that chemolithotrophs have evolved to utilize from inorganic substrates, such as sulfur. In chemolithotrophs, the compounds - the electron donors - are oxidized in the cell, and the electrons are channeled into respiratory chains, ultimately producing ATP. The electron acceptor can be oxygen (in aerobic bacteria), but a variety of other electron acceptors, organic and inorganic, are also used by various species. Aerobic bacteria such as the nitrifying bacteria, "Nitrobacter", utilize oxygen to oxidize nitrite to nitrate. Some lithotrophs produce organic compounds from carbon dioxide in a process called chemosynthesis, much as plants do in photosynthesis. Plants use

neg: Obligate anaerobe attributed to a combination of factors: Obligate anaerobes metabolise energy by anaerobic respiration or fermentation. In aerobic respiration, the pyruvate generated from glycolysis is converted to acetyl-CoA. This is then broken down via the TCA cycle and electron transport chain. Anaerobic respiration differs from aerobic respiration in that it uses an electron acceptor other than oxygen in the electron transport chain. Examples of alternative electron acceptors include sulfate, nitrate, iron, manganese, mercury, and carbon monoxide. Fermentation differs from anaerobic respiration in that the pyruvate generated from glycolysis is broken down without the involvement of an electron transport chain (i.e. there

neg: Microbial metabolism Proteobacteria. Most microbes respire (use an electron transport chain), although oxygen is not the only terminal electron acceptor that may be used. As discussed below, the use of terminal electron acceptors other than oxygen has important biogeochemical consequences. Fermentation is a specific type of heterotrophic metabolism that uses organic carbon instead of oxygen as a terminal electron acceptor. This means that these organisms do not use an electron transport chain to oxidize NADH to and therefore must have an alternative method of using this reducing power and maintaining a supply of for the proper functioning of normal metabolic pathways (e.g.

neg: Electron transport chain proton gradient). ATP synthase is also readily reversible. Thus ATP can be used to build a proton gradient, which in turn can be used to make NADH. This process of "reverse electron transport" is important in many prokaryotic electron transport chains. In eukaryotes, NADH is the most important electron donor. The associated electron transport chain is NADH → "Complex I" → Q → "Complex III" → cytochrome "c" → "Complex IV" → O where "Complexes I, III" and" IV" are proton pumps, while Q and cytochrome "c" are mobile electron carriers. The electron acceptor is molecular oxygen. In prokaryotes (bacteria

neg: Propanil I reaction a chlorophyll molecule absorbs one photon (light) and loses one electron, starting an electron transport chain reaction leading to the stage II reactions. Propanil inhibits the electron transport chain reaction and its conversion of CO to carbohydrate precursors. That inhibits further development of the weed. Rice is relatively immune to propanil but most weeds are susceptible to it. The reason for the selectivity is that rice contains a high level of the enzyme aryl acylamidase (AAA), which rapidly metabolizes propanil to relativity nontoxic 3,4-dichloroaniline. Susceptible weeds lack the gene(s) coding for the AAA enzyme and thus succumb to

neg: Syntrophococcus sucromutans its title as an acetogen. The unique aspect of its acetate production is that it can synthesize many of these organic products from one-carbon compounds. Another set of electron acceptors consists of the methoxyl groups on benzenoid compounds, converting those groups into hydroxyl groups. Below is a table of potential electron acceptors and to what "S. sucromutans" reduces them. Its electron acceptors were characterized by its discoverers Krumholz and Bryant, who used ultraviolet absorbance to measure caffeate disappearance, thin layer chromatography to identify benzenoids, and the phenol sulphuric method for determining carbohydrate content. Its third option is to donate these

neg: Halorespiration a nontoxic chemical, have been isolated. They have been found to belong to the genus "Dehalococcoides" and to use H as their electron donor. The process of dehalorespiration has been applied to in situ bioremediation of PCE and TCE in the past. For example, enhanced reductive dechlorination has been used to treat contaminated groundwater by introducing electron donors and dehalorespiring bacteria into the contaminated site, to create conditions that stimulate bacterial growth and dehalorespiration. In enhanced reductive dechlorination, the pollutants act as the electron acceptors and are completely reduced to ultimately produce ethene in a series of reactions. An ecologically

neg: Abiogenesis of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments..." These form where hydrogen-rich fluids emerge from below the sea floor, as a result of serpentinization of ultra-mafic olivine with seawater and a pH interface with carbon dioxide-rich ocean water. The vents form a sustained chemical energy source derived from redox reactions, in which electron donors (molecular hydrogen) react with electron acceptors (carbon dioxide); see Iron–sulfur world theory. These are highly exothermic reactions. Michael Russell demonstrated that alkaline vents created an abiogenic proton motive force (PMF) chemiosmotic gradient, in which conditions are ideal for

neg: Bioremediation acceptor is reduced. Common electron acceptors in bioremediation processes include oxygen, nitrate, manganese (III and IV), iron (III), sulfate, carbon dioxide and some pollutants (chlorinated solvents, explosives, oxidized metals, and radionuclides). Electron donors include sugars, fats, alcohols, natural organic material, fuel hydrocarbons and a variety of reduced organic pollutants. The redox potential for common biotransformation reactions is shown in the table. Aerobic bioremediation is the most common form of oxidative bioremediation process where oxygen is provided as the electron acceptor for oxidation of petroleum, polyaromatic hydrocarbons (PAHs), phenols, and other reduced pollutants. Oxygen is generally the preferred electron acceptor because

neg: Anoxygenic photosynthesis transport chain, proteins such as halorhodopsin capture light energy with the aid of diterpenes to move ions against the gradient and produce ATP via chemiosmosis in the manner of mitochondria. There are two main types of anaerobic photosynthetic electron transport chains in bacteria. The type I reaction centers found in GSB, Chloracidobacterium, and Heliobacteria and the type II reaction centers found in FAPs and Purple Bacteria Type I Reaction Centers The electron transport chain of green sulfur bacteria — such as is present in model organism "Chlorobaculum tepidum" — uses the reaction centre bacteriochlorophyll pair, P840. When light is absorbed

neg: Sulfate-reducing microorganisms reduce sulfate in large amounts to obtain energy and expel the resulting sulfide as waste; this is known as dissimilatory sulfate reduction. They use sulfate as the terminal electron acceptor of their electron transport chain. Most of them are anaerobes; however there are examples of sulfate-reducing microorganisms that are tolerant of oxygen, and some of them can even perform aerobic respiration. No growth is observed when oxygen is used as the electron acceptor. In addition, there are sulfate-reducing microorganisms that can also reduce other electron acceptors, such as fumarate, nitrate (NO), nitrite (NO), ferric iron [Fe(III)], and dimethyl sulfoxide. In

neg: Dehydrogenase releasing a proton, H, but dehydrogenases can also transfer two hydrogens, using FAD as an electron acceptor. This would be depicted as AH + B ↔ A + BH. A double bond is normally formed in between the two atoms that the hydrogens were taken from, as in the case of succinate dehydrogenase. The two hydrogens have been transferred to the carrier or the other product, with their electrons. The distinction between the subclasses of oxidoreductases that catalyze oxidation reactions lies in their electron acceptors. Dehydrogenase and oxidase are easily distinguishable if one considers the electron acceptor. An oxidase will

neg: Oxidative phosphorylation Oxidative phosphorylation Oxidative phosphorylation (UK , US ) is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing energy which is used to produce adenosine triphosphate (ATP). In most eukaryotes, this takes place inside mitochondria. Almost all aerobic organisms carry out oxidative phosphorylation. This pathway is probably so pervasive because it is a highly efficient way of releasing energy, compared to alternative fermentation processes such as anaerobic glycolysis. 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

neg: Photosynthesis surface of the leaf is coated with a water-resistant waxy cuticle that protects the leaf from excessive evaporation of water and decreases the absorption of ultraviolet or blue light to reduce heating. The transparent epidermis layer allows light to pass through to the palisade mesophyll cells where most of the photosynthesis takes place. In the light-dependent reactions, one molecule of the pigment chlorophyll absorbs one photon and loses one electron. This electron is passed to a modified form of chlorophyll called pheophytin, which passes the electron to a quinone molecule, starting the flow of electrons down an electron transport chain

neg: Hill reaction by an artificial electron acceptor such as DCPIP, again allowing for the discharge of oxygen. The technique of replacing the natural electron acceptors with artificial electron acceptors can be used in the laboratory to provide a means to measure phosphorylation in chloroplasts and observe its relation to the discharge of oxygen in this reaction. Hill's finding was that the origin of oxygen in photosynthesis is water (HO) not carbon dioxide (CO) as previously believed. Hill's reaction also demonstrates that the light dependent redox reaction is the first reaction to take place in photosynthesis. The electrons thus freed by the splitting

neg: Light-dependent reactions is, the electron on the acceptor could move back to neutralize the positive charge on the special pair. Its return to the special pair would waste a valuable high-energy electron and simply convert the absorbed light energy into heat. In the case of PSII, this backflow of electrons can produce reactive oxygen species leading to photoinhibition. Three factors in the structure of the reaction center work together to suppress charge recombination nearly completely. Thus, electron transfer proceeds efficiently from the first electron acceptor to the next, creating an electron transport chain that ends if it has reached NADPH. The photosynthesis

neg: Photosystem II light-harvesting protein significantly increases the light-harvesting system of PSI. IsiA can also provide photoprotection for PSII. Plants, algae and some bacteria use two photosystems, PSI with P700 and PSII with P680. Using light energy, PSII acts first to channel an electron through a series of acceptors that drive a proton pump to generate ATP, before passing the electron on to PSI. Once the electron reaches PSI it has used most of its energy in producing ATP, but a second photon of light captured by P700 provides the required energy to channel the electron to ferredoxin, generating reducing power in the form of

neg: Light-dependent reactions transfers the electron from PSII to the proton pump, cytochrome b6f. The ultimate electron donor of PSII is water. Cytochrome b6f proceeds the electron chain to PSI through plastocyanin molecules. PSI is able to continue the electron transfer in two different ways. It can transfer the electrons either to plastoquinol again, creating a cyclic electron flow, or to an enzyme called FNR (Ferredoxin—NADP(+) reductase), creating a non-cyclic electron flow. PSI releases FNR into the stroma, where it reduces to NADPH. Activities of the electron transport chain, especially from cytochrome b6f, lead to pumping of protons from the stroma to the

neg: Electron acceptor an exothermic reaction, the energy liberated is of interest and is equal to formula_2. In chemistry, a class of electron acceptors that acquire not just one, but a set of two paired electrons that form a covalent bond with an electron donor molecule, is known as a Lewis acid. This phenomenon gives rise to the wide field of Lewis acid-base chemistry. The driving forces for electron donor and acceptor behavior in chemistry is based on the concepts of electropositivity (for donors) and electronegativity (for acceptors) of atomic or molecular entities. Examples of electron acceptors include oxygen, nitrate, iron (III), manganese

neg: Light-independent reactions Light-independent reactions The light-independent reactions, or dark reactions, of photosynthesis are chemical reactions that convert carbon dioxide and other compounds into glucose. These reactions occur in the stroma, the fluid-filled area of a chloroplast outside the thylakoid membranes. These reactions take the products (ATP and NADPH) of light-dependent reactions and perform further chemical processes on them. These reactions are closely coupled to the thylakoid electron transport chain as reducing power provided by NADPH produced in the photosystem I is actively needed. The process of photorespiration, also known as C2 cycle, is also coupled to the dark reactions, as it results

neg: Light-dependent reactions Rather, they bear a striking resemblance to chloroplasts themselves. This suggests that organisms resembling cyanobacteria were the evolutionary precursors of chloroplasts. One imagines primitive eukaryotic cells taking up cyanobacteria as intracellular symbionts in a process known as endosymbiosis. Cyanobacteria contain structures similar to PS II and PS I in chloroplasts. Their light-harvesting system is different from that found in plants (they use "phycobilins", rather than chlorophylls, as antenna pigments), but their electron transport chain is, in essence, the same as the electron transport chain in chloroplasts. The mobile water-soluble electron carrier is cytochrome " in cyanobacteria, plastocyanin in plants. Cyanobacteria

neg: Light-independent reactions the stroma caused by its phosphorylation. Light-independent reactions The light-independent reactions, or dark reactions, of photosynthesis are chemical reactions that convert carbon dioxide and other compounds into glucose. These reactions occur in the stroma, the fluid-filled area of a chloroplast outside the thylakoid membranes. These reactions take the products (ATP and NADPH) of light-dependent reactions and perform further chemical processes on them. These reactions are closely coupled to the thylakoid electron transport chain as reducing power provided by NADPH produced in the photosystem I is actively needed. The process of photorespiration, also known as C2 cycle, is also coupled to

neg: Electron donor acceptor molecule, is known as a Lewis base. This phenomenon gives rise to the wide field of Lewis acid-base chemistry. The driving forces for electron donor and acceptor behavior in chemistry is based on the concepts of electropositivity (for donors) and electronegativity (for acceptors) of atomic or molecular entities. In biology, electron donors release an electron during cellular respiration, resulting in the release of energy. Microorganisms, such as bacteria, obtain energy in the electron transfer processes. Through its cellular machinery, the microorganism collects the energy for its use. The final result is the electron is donated to an electron acceptor.

neg: Polymer-fullerene bulk heterojunction solar cells donors with high electron affinity fullerene derivatives as acceptors to extend the spectral sensitivity. Ternary solar cells are a promising approach to increased efficiency and light harvesting properties of organic photovoltaic cells (OPV). Polymer-fullerene bulk heterojunction solar cells Polymer-fullerene bulk heterojunction solar cells are a type of solar cell researched in academic laboratories. Photovoltaic cells featuring a polymeric blend of organics have shown promise in a field largely dominated by inorganic (e.g. silicon) solar cells. Specifically, fullerene derivatives act as electron acceptors for donor materials like P3HT (poly-3-hexyl thiophene-2,5-diyl), creating a polymer-fullerene based photovoltaic cell. Some of the improvements that

neg: Lily Young microorganisms in the environment are essentially carrying out oxidation and reduction reactions, namely, oxidation of the organic contaminant coupled to the reduction of inorganic electron acceptors. The mechanism by which these bacteria (mainly denitrifiers, iron reducers, sulfidogens and methanogens, respectively) degrade the contaminants is different from aerobic bacteria because they cannot use oxygen to activate the stable hydrocarbon molecules. In contrast to humans, these bacteria are not dependent on oxygen as an electron acceptor for cellular respiration, but use molecules like nitrate, iron, sulfate and carbonate. During her early research in the Environmental Engineering Program at Stanford University her groups

neg: Electron transport chain chain electrons move from an electron donor (NADH or QH) to a terminal electron acceptor (O) via a series of redox reactions. These reactions are coupled to the creation of a proton gradient across the mitochondrial inner membrane. There are three proton pumps: "I", "III", and "IV". The resulting transmembrane proton gradient is used to make ATP via ATP synthase. The reactions catalyzed by "Complex I" and "Complex III" work roughly at equilibrium. This means that these reactions are readily reversible, by increasing the concentration of the products relative to the concentration of the reactants (for example, by increasing the

neg: Contorted aromatics properties of nanoscale phase separation, charge separation and charge transport in films. The concave discs can behave as molecular sensors for electron deficient aromatic molecules. Once in contact with electron acceptors like fullerenes they show typical characteristics of a p-n junction in shape of a ball and socket joint model Figure 7. The ribbons, on the other hand, can be envisioned as pieces of graphene being spun into ribbons owing to contortions. They are good materials for OFETs as electron transporting materials. With the incorporation of donor polymers they behave as potential alternative for non-fullerene based organic solar cells. The

neg: Microbial metabolism The APS is then reduced by the enzyme APS reductase to form sulfite () and AMP. In organisms that use carbon compounds as electron donors, the ATP consumed is accounted for by fermentation of the carbon substrate. The hydrogen produced during fermentation is actually what drives respiration during sulfate reduction. Acetogenesis is a type of microbial metabolism that uses hydrogen () as an electron donor and carbon dioxide () as an electron acceptor to produce acetate, the same electron donors and acceptors used in methanogenesis (see above). Bacteria that can autotrophically synthesize acetate are called homoacetogens. Carbon dioxide reduction in

neg: Thylakoid to the separate location of the two photosystems in the thylakoid membrane system, mobile electron carriers are required to shuttle electrons between them. These carriers are plastoquinone and plastocyanin. Plastoquinone shuttles electrons from photosystem II to the cytochrome b6f complex, whereas plastocyanin carries electrons from the cytochrome b6f complex to photosystem I. Together, these proteins make use of light energy to drive electron transport chains that generate a chemiosmotic potential across the thylakoid membrane and NADPH, a product of the terminal redox reaction. The ATP synthase uses the chemiosmotic potential to make ATP during photophosphorylation. These photosystems are light-driven redox

neg: Archaea as a result of metabolism) living in anaerobic environments, such as swamps. This form of metabolism evolved early, and it is even possible that the first free-living organism was a methanogen. A common reaction involves the use of carbon dioxide as an electron acceptor to oxidize hydrogen. Methanogenesis involves a range of coenzymes that are unique to these archaea, such as coenzyme M and methanofuran. Other organic compounds such as alcohols, acetic acid or formic acid are used as alternative electron acceptors by methanogens. These reactions are common in gut-dwelling archaea. Acetic acid is also broken down into methane and

neg: P700 cluster proteins as terminal electron acceptors. Photosystem I is more complex than photosystem II (P680), as it has a more complex antenna system, has more subunits in its overall structure, and may exhibit cyclic or non-cyclic electron transfer from the excited P700* to the electron acceptor. P700 P700, or photosystem I primary donor, (where P stands for pigment) is the reaction-center chlorophyll "a" molecule in association with photosystem I. Its absorption spectrum peaks at 700 nm. When photosystem I absorbs light, an electron is excited to a higher energy level in the P700 chlorophyll. The resulting P700 with excited electron

neg: Contorted aromatics due to resonance of electrons and hinder the possibility of electron hole pair recombination for having suitable HOMO and LUMO offsets at donor and acceptor interphase while allowing the antagonistic charge percolation pathways. These contorted molecules show remarkable phenomenon of self- assembly. Based upon the data collected from OFET and OPVs, these molecules show efficient charge transport. The c-HBC, c-OCBC and c-DBTTC act as electron donors and c-PDIs as electron acceptors. The contorted non-planar structure allows these molecules to express sufficient charge transport in self-assembled layers. The self-assembly characteristics change in case of alkyl chain derivatives of c-HBC into orthorhombic

neg: Photophosphorylation Photophosphorylation In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation. Only two sources of energy are available to living organisms: sunlight and reduction-oxidation (redox) reactions. All organisms produce ATP, which is the universal energy currency of life. Commonly in photosynthesis this involves photolysis, or photodissociation, of water and a continuous unidirectional flow of electrons from water to PSII . In photophosphorylation, light energy is used to create a high-energy electron donor and a lower-energy electron acceptor. Electrons then move spontaneously from donor to acceptor through an electron transport chain.

neg: Light-dependent reactions electron transport") or back to cytochrome "" ("cyclic electron transport"): PS I, like PS II, is a complex, highly organized transmembrane structure that contains antenna chlorophylls, a reaction center (P700), phylloquinine, and a number of iron-sulfur proteins that serve as intermediate redox carriers. The light-harvesting system of PS I uses multiple copies of the same transmembrane proteins used by PS II. The energy of absorbed light (in the form of delocalized, high-energy electrons) is funneled into the reaction center, where it excites special chlorophyll molecules (P700, maximum light absorption at 700 nm) to a higher energy level. The process occurs

neg: Microbial metabolism and . While aerobic organisms during respiration use oxygen as a terminal electron acceptor, anaerobic organisms use other electron acceptors. These inorganic compounds have a lower reduction potential than oxygen, meaning that respiration is less efficient in these organisms and leads to slower growth rates than aerobes. Many facultative anaerobes can use either oxygen or alternative terminal electron acceptors for respiration depending on the environmental conditions. Most respiring anaerobes are heterotrophs, although some do live autotrophically. All of the processes described below are dissimilative, meaning that they are used during energy production and not to provide nutrients for the cell

neg: Photoinhibition acceptor of Photosystem II. The protonated and double-reduced forms of Q do not function in electron transport. Furthermore, charge recombination reactions in inhibited Photosystem II are expected to lead to the triplet state of the primary donor (P) more probably than same reactions in active PSII. Triplet P may react with oxygen to produce harmful singlet oxygen. If the oxygen-evolving complex is chemically inactivated, then the remaining electron transfer activity of PSII becomes very sensitive to light. It has been suggested that even in a healthy leaf, the oxygen-evolving complex does not always function in all PSII centers, and those

neg: Hill reaction electron acceptor, such as a dye that changes color when it is reduced. These are known as Hill reagents. The Hill reagent was discovered in 1937 by Robin Hill. These dyes permitted the finding of electron transport chains during photosynthesis. dichlorophenolindophenol (DCPIP), an example of these dyes, is widely used by experimenters. DCPIP is a dark blue solution that becomes lighter as it is reduced. It gives experimenters a simple visual test and observation of the light reaction. In another approach to studying photosynthesis, light-absorbing pigments such as chlorophyll can be extracted from the chloroplasts of plant leaves or other

neg: Acetobacterium is that it conserves energy by using an Rnf complex to create a sodium gradient rather than a proton gradient. This means that "A.woodii" would need sodium in its environment in order to make ATP. When reducing CO to acetate the "Acetobacterium" uses the Wood–Ljungdahl pathway with CO as the electron acceptor. However, the Acetobacterium can use other electron acceptors like caffeate. To use caffeate as an electron acceptor the bacterium couples hydrogen dependent caffeate reduction with electrons from hydrogen and uses sodium ions as coupling ions. The step in the electron transport chain that creates the sodium gradient is

neg: Electron donor During this process (electron transport chain) the electron donor is oxidized and the electron acceptor is reduced. Petroleum hydrocarbons, less chlorinated solvents like vinyl chloride, soil organic matter, and reduced inorganic compounds are all compounds that can act as electron donors. These reactions are of interest not only because they allow organisms to obtain energy, but also because they are involved in the natural biodegradation of organic contaminants. When clean-up professionals use monitored natural attenuation to clean up contaminated sites, biodegradation is one of the major contributing processes. Electron donor An electron donor is a chemical entity that donates electrons

neg: Trimethylenemethane cycloaddition Trimethylenemethane cycloaddition Trimethylenemethane cycloaddition is the formal [3+2] annulation of trimethylenemethane (TMM) derivatives to two-atom pi systems. Although TMM itself is too reactive and unstable to be stored, reagents which can generate TMM or TMM synthons "in situ" can be used to effect cycloaddition reactions with appropriate electron acceptors. Generally, electron-deficient pi bonds undergo cyclization with TMMs more easily than electron-rich pi bonds. Trimethylenemethane is a neutral, four-carbon molecule composed of four pi bonds; thus, it must be expressed either as a non-Kekulé molecule or a zwitterion. The orbital energy levels of TMM reveal that it possesses singlet and triplet

neg: Photosynthetic reaction centre pigment molecules, or passed to them by resonance transfer from a surrounding light-harvesting complex, they release two electrons into an electron transport chain. Light is made up of small bundles of energy called photons. If a photon with the right amount of energy hits an electron, it will raise the electron to a higher energy level. Electrons are most stable at their lowest energy level, what is also called its ground state. In this state, the electron is in the orbit that has the least amount of energy. Electrons in higher energy levels can return to ground state in a

neg: Contorted aromatics of exciton recombination in fullerenes-based electron acceptors. Contrary to the inorganic semiconductors, the excitons formed in organic materials possess a higher binding energy (0.3-1.0 eV). This issue is resolved at the acceptor donor interface by matching HOMO (donor) and LUMO (acceptor) energy gaps. Planar heterojunction (PHJ) is the commonly used OPV architecture in which donor and acceptors molecules are joined with one another. The contorted PAHs owing to their non-polar and non-planar topology and shape are expected to offer a balance between miscibility and self-aggregation for optimal charge transport to electrodes. These contorted conjugated aromatic molecules support the charge transport

neg: Geothrix fermentans electron acceptor. "G. fermentans" can also grow using other forms of iron and metals such as manganese, but it shows preference for iron or iron derivatives. Utilization of alternate electron acceptors by this organism depends on the electron donor present. For instance, it will utilize nitrate (NO) and Mn(IV) as alternative electron acceptors when lactate is being used as the electron donor. "G. fermentans", though it shares similar reduction processes as the other DIRB, displays metabolic characteristics that set it apart from other iron reducers. In the process of respiration, this organism is capable of complete oxidation of the before-mentioned

neg: High potential iron-sulfur protein Chromatium, and Ectothiorhodospira. HiPIPs are periplasmic proteins in photosynthetic bacteria. They play a role of electron shuttles in the cyclic electron flow between the photosynthetic reaction center and the cytochrome bc1 complex. Other oxidation reactions HiPIP involved include catalyzing Fe(II) oxidation, being electron donor to reductase and electron accepter for some thiosulfate-oxidizing enzyme. High potential iron-sulfur protein High potential iron-sulfur proteins (HIPIP) are a specific class of high-redox potential 4Fe-4S ferredoxins that functions in anaerobic electron transport and which occurs in photosynthetic bacteria and in "Paracoccus denitrificans". The HiPIPs are small proteins which show significant variation in their sequences, their

neg: Bioelectrochemical reactor process is called respiration. If the process is internal, electron transfer is called fermentation. The microorganism attempt to maximize their energy gain by selecting the electron acceptor with the highest potential available. In nature mainly minerals containing iron or manganese oxides are being reduced. Often soluble electron acceptors are depleted in the microbial environment. The microorganism can also maximize their energy selecting a good electron donor which can be easily metabolized. These processes are done by extracellular electron transfer (EET). The theoretical energy gain ΔG for microorganisms relates directly the potential difference between the electron acceptor and the donor. But

neg: Bioremediation of radioactive waste and currently being set up as an ecological and economic alternative to traditional procedures. Physico-chemical conventional strategies are based on the extraction of waste by excavating and drilling, with a subsequent long-range transport for their final confinement. These works and transport have often unacceptable estimated costs of operation that could exceed a trillion dollars in the US and 50 million pounds in the UK. The species involved in these processes have the ability to influence the properties of radionuclides such as solubility, bioavailability and mobility to accelerate its stabilization. Its action is largely influenced by electron donors and acceptors, nutrient

neg: Physical organic chemistry and bases are relevant to physical organic chemistry. Organic chemists are primarily concerned with Brønsted–Lowry acids/bases as proton donors/acceptors and Lewis acids/bases as electron acceptors/donors in organic reactions. Chemists use a series of factors developed from physical chemistry -- electronegativity/Induction, bond strengths, resonance, hybridization, aromaticity, and solvation—to predict relative acidities and basicities. The hard/soft acid/base principle is utilized to predict molecular interactions and reaction direction. In general, interactions between molecules of the same type are preferred. That is, hard acids will associate with hard bases, and soft acids with soft bases. The concept of hard acids and bases is often

neg: Light-dependent reactions can also synthesize ATP by oxidative phosphorylation, in the manner of other bacteria. The electron transport chain is where the mobile electron carriers are plastoquinone and cytochrome ', while the proton pumps are NADH dehydrogenase, ' and cytochrome ". Cyanobacteria are the only bacteria that produce oxygen during photosynthesis. Earth's primordial atmosphere was anoxic. Organisms like cyanobacteria produced our present-day oxygen-containing atmosphere. The other two major groups of photosynthetic bacteria, purple bacteria and green sulfur bacteria, contain only a single photosystem and do not produce oxygen. Purple bacteria contain a single photosystem that is structurally related to PS II in

neg: Electrochemical gradient 200mV. This drives the flux of protons back into the matrix through ATP synthase which produces ATP by adding an inorganic phosphate to ADP. Thus, generation of a proton electrochemical gradient is crucial for energy production in mitochondria. The total equation for the electron transport chain is: Similar to the electron transport chain, the light-dependent reactions of photosynthesis pump protons into the thylakoid lumen of chloroplasts to drive the synthesis of ATP by ATP synthase. The proton gradient can be generated through either noncyclic or cyclic photophosphorylation. Of the proteins that participate in noncyclic photophosphorylation, photosystem II (PSII), plastiquinone, and

neg: Permeable reactive barrier of other molecules can serve as electron acceptors. Oxygen is preferentially utilized over the anaerobic electron acceptors because using oxygen gives more energy and, as an added benefit, results in faster contaminants oxidation rates. Unfortunately, the available oxygen is often not sufficient for the contaminants in highly contaminated areas, and as a result the anaerobic electron acceptors must be utilized. Reactive barriers containing oxygen-releasing compounds have been used successfully to stimulate aerobic biodegradation of monoaromatic hydrocarbons. Clays, zeolites, and other natural material have a high capacity for cation exchange. They do this by creating a net negative charge by substituting

neg: Oxidative phosphorylation oxygen, while pumping protons across the membrane. 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: Many eukaryotic organisms have electron transport chains that differ from the much-studied mammalian enzymes described above. For example, plants have alternative NADH oxidases, which oxidize NADH in the cytosol rather than in the mitochondrial matrix, and pass