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Anoxygenic Photosynthesis
Bacterial anoxygenic photosynthesis differs from the better known oxygenic photosynthesis in plants by the reductant used (e.g. hydrogen sulfide instead of water) and the byproduct generated (e.g. elemental sulfur instead of molecular oxygen). Bacteria and archaea Several groups of bacteria can conduct anoxygenic photosynthesis: green sulfur bacteria (GSB), red and green filamentous phototrophs (FAPs e.g. Chloroflexia), purple bacteria, acidobacteriota, and heliobacteria. Some archaea (e.g. ''Halobacterium'') capture light energy for metabolic function and are thus phototrophic but none are known to "fix" carbon (i.e. be photosynthetic). Instead of a chlorophyll-type receptor and electron transport chain, proteins such as halorhodopsin capture light energy with the aid of diterpenes to move ions against a gradient and produce ATP via chemiosmosis in the manner of mitochondria. Pigments The pigments used to carry out anaerobic photosynthesis are similar to chlorophyll but diffe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemiosmosis
Chemiosmosis is the movement of ions across a semipermeable membrane bound structure, down their electrochemical gradient. An important example is the formation of adenosine triphosphate (ATP) by the movement of hydrogen ions (H+) across a membrane during cellular respiration or photosynthesis. Hydrogen ions, or protons, will diffuse from a region of high proton concentration to a region of lower proton concentration, and an electrochemical concentration gradient of protons across a membrane can be harnessed to make ATP. This process is related to osmosis, the movement of water across a selective membrane, which is why it is called "chemiosmosis". ATP synthase is the enzyme that makes ATP by chemiosmosis. It allows protons to pass through the membrane and uses the free energy difference to phosphorylate adenosine diphosphate (ADP), making ATP. The generation of ATP by chemiosmosis occurs in mitochondria and chloroplasts, as well as in most bacteria and archaea. For instan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrochemical Gradient
An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts, the chemical gradient, or difference in solute concentration across a membrane, and the electrical gradient, or difference in charge across a membrane. When there are unequal concentrations of an ion across a permeable membrane, the ion will move across the membrane from the area of higher concentration to the area of lower concentration through simple diffusion. Ions also carry an electric charge that forms an electric potential across a membrane. If there is an unequal distribution of charges across the membrane, then the difference in electric potential generates a force that drives ion diffusion until the charges are balanced on both sides of the membrane. Electrochemical gradients are essential to the operation of batteries and other electrochemical cells, photosynthesis and cellular respiration, and certain other ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Transport Chain
An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H+ ions) across a membrane. The electrons that transferred from NADH and FADH2 to the ETC involves 4 multi-subunit large enzymes complexes and 2 mobile electron carriers. Many of the enzymes in the electron transport chain are membrane-bound. The flow of electrons through the electron transport chain is an exergonic process. The energy from the redox reactions creates an electrochemical proton gradient that drives the synthesis of adenosine triphosphate (ATP). In aerobic respiration, the flow of electrons terminates with molecular oxygen as the final electron acceptor. In anaerobic respiration, other electron acceptors are used, such as sulfate. In an electron transport chain, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Transfer
Electron transfer (ET) occurs when an electron relocates from an atom or molecule to another such chemical entity. ET is a mechanistic description of certain kinds of redox reactions involving transfer of electrons. Electrochemical processes are ET reaction. ET reactions are relevant to photosynthesis and respiration. ET reactions commonly involve transition metal complexes, In organic chemistry ET is a step in some commercial polymerization reactions. It is foundational to photoredox catalysis. Classes of electron transfer Inner-sphere electron transfer In inner-sphere ET, the two redox centers are covalently linked during the ET. This bridge can be permanent, in which case the electron transfer event is termed intramolecular electron transfer. More commonly, however, the covalent linkage is transitory, forming just prior to the ET and then disconnecting following the ET event. In such cases, the electron transfer is termed intermolecular electron transfer. A famous ex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxygen-evolving Complex
The oxygen-evolving complex (OEC), also known as the water-splitting complex, is the portion of photosystem II where photo-oxidation of water occurs during the light reactions of photosynthesis. The OEC is surrounded by four core protein subunits of photosystem II at the membrane-lumen interface. In the overall water oxidation reaction, four electrons are extracted from two water molecules so that four protons and one O2 molecule are produced. The molecular machinery for oxidizing water requires the ability to store the oxidizing potential resulting from three light-induced charge separations before the fourth provides sufficient oxidizing power for water oxidation. Species distribution and subcellular location The OEC and Photosystem II are only found in chloroplasts and cyanobacteria. Within the chloroplasts, Photosystem II spans the thylakoid membrane, composed of both granal thylakoids and stromal thylakoids. Structure The OEC has a metalloenzyme core containing both ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photosystem II
Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem, enzymes capture photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce plastoquinone to plastoquinol. The energized electrons are replaced by oxidizing water to form hydrogen ions and molecular oxygen. By replenishing lost electrons with electrons from the splitting of water, photosystem II provides the electrons for all of photosynthesis to occur. The hydrogen ions (protons) generated by the oxidation of water help to create a proton gradient that is used by ATP synthase to generate ATP. The energized electrons transferred to plastoquinone are ultimately used to reduce to NADPH or are used in non-cyclic electron flow. DCMU is a chemical often used in laborator ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cytochrome
Cytochromes are redox-active proteins containing a heme, with a central Fe atom at its core, as a cofactor. They are involved in electron transport chain and redox catalysis. They are classified according to the type of heme and its mode of binding. Four varieties are recognized by the International Union of Biochemistry and Molecular Biology (IUBMB), cytochromes a, cytochromes b, cytochromes c and cytochrome d. Cytochrome function is linked to the reversible redox change from ferrous (Fe(II)) to the ferric (Fe(III)) oxidation state of the iron found in the heme core. In addition to the classification by the IUBMB into four cytochrome classes, several additional classifications such as cytochrome o and cytochrome P450 can be found in biochemical literature. History Cytochromes were initially described in 1884 by Charles Alexander MacMunn as respiratory pigments (myohematin or histohematin). In the 1920s, Keilin rediscovered these respiratory pigments and named them the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photosynthetic Reaction Centre
A photosynthetic reaction center is a complex of several proteins, pigments and other co-factors that together execute the primary energy conversion reactions of photosynthesis. Molecular excitations, either originating directly from sunlight or transferred as excitation energy via light-harvesting antenna systems, give rise to electron transfer reactions along the path of a series of protein-bound co-factors. These co-factors are light-absorbing molecules (also named chromophores or pigments) such as chlorophyll and pheophytin, as well as quinones. The energy of the photon is used to excite an electron of a pigment. The free energy created is then used, via a chain of nearby electron acceptors, for a transfer of hydrogen atoms (as protons and electrons) from H2O or hydrogen sulfide towards carbon dioxide, eventually producing glucose. These electron transfer steps ultimately result in the conversion of the energy of photons to chemical energy. Transforming light energy into ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blue-green algae, although they are not usually scientifically classified as algae. They appear to have originated in a freshwater or terrestrial environment. Sericytochromatia, the proposed name of the paraphyletic and most basal group, is the ancestor of both the non-photosynthetic group Melainabacteria and the photosynthetic cyanobacteria, also called Oxyphotobacteria. Cyanobacteria use photosynthetic pigments, such as carotenoids, phycobilins, and various forms of chlorophyll, which absorb energy from light. Unlike heterotrophic prokaryotes, cyanobacteria have internal membranes. These are flattened sacs called thylakoids where photosynthesis is performed. Phototrophic eukaryotes such as green plants perform photosynthesis in pl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near-infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around 1 millimeter (300 GHz) to the nominal red edge of the visible spectrum, around 700 nanometers (430 Terahertz (unit), THz). Longer IR wavelengths (30 μm-100 μm) are sometimes included as part of the terahertz radiation range. Almost all black-body radiation from objects near room temperature is at infrared wavelengths. As a form of electromagnetic radiation, IR propagates energy and momentum, exerts radiation pressure, and has properties corresponding to Wave–particle duality, both those of a wave and of a Subatomic particle, particle, the photon. It was long known that fires emit invisible heat; in 1681 the pioneering experimenter Edme Mariotte showed that glass, though transparent to sunlight, obstructed rad ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
