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Photophosphorylation
In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation. Cyclic photophosphorylation occurs in both aerobic and anaerobic conditions, driven by the main primary source of energy available to living organisms, which is sunlight. All organisms produce a phosphate compound, ATP, which is the universal energy currency of life. In photophosphorylation, light energy is used to pump protons across a biological membrane, mediated by flow of electrons through an electron transport chain. This stores energy in a proton gradient. As the protons flow back through an enzyme called ATP synthase, ATP is generated from ADP and inorganic phosphate. ATP is essential in the Calvin cycle to assist in the synthesis of carbohydrates from carbon dioxide and NADPH. ATP and reactions Both the structure of ATP synthase and its underlying gene are remarkably similar in all known forms of life. ATP synthase is powered by a trans ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photosynthesis
Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabolism. ''Photosynthesis'' usually refers to oxygenic photosynthesis, a process that produces oxygen. Photosynthetic organisms store the chemical energy so produced within intracellular organic compounds (compounds containing carbon) like sugars, glycogen, cellulose and starches. To use this stored chemical energy, an organism's cells metabolize the organic compounds through cellular respiration. Photosynthesis plays a critical role in producing and maintaining the oxygen content of the Earth's atmosphere, and it supplies most of the biological energy necessary for complex life on Earth. Some bacteria also perform anoxygenic photosynthesis, which uses bacteriochlorophyll to split hydrogen sulfide as a reductant instead of water, p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proton 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. * The electrical gradient, or difference in charge across a membrane. If 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 othe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Otto Kandler
Otto Kandler (23 October 1920 in Deggendorf – 29 August 2017 in Munich, Bavaria) was a Germans, German botanist and microbiologist. Until his retirement in 1986 he was professor of botany at the Ludwig Maximilian University of Munich. His most important research topics were photosynthesis, plant carbohydrate metabolism, analysis of the structure of bacterial cell walls (murein/peptidoglycan), the systematics of ''Lactobacillus'', and the chemotaxonomy of plants and microorganisms. He presented the first experimental evidence for the existence of photophosphorylation ''in vivo''. His discovery of the basic differences between the cell walls of bacteria and archaea (up to 1990 called "archaebacteria") convinced him that archaea represent an autonomous group of organisms distinct from bacteria. This was the basis for his cooperation with Carl Woese and made him the founder of research on the ''Archaea'' in Germany. In 1990, together with Woese, he proposed the three Domain (biolo ... [...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, adenosine triphosphate (ATP) by the movement of hydrogen ions (H+) across a Inner nuclear membrane, membrane during cellular respiration or photosynthesis. Hydrogen ions, or protons, will diffusion, diffuse from a region of high proton concentration to a region of lower proton concentration, and an electrochemical gradient, 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 Thermodynamic free energy, free energy difference to convert phosphorylate adenosine diphosphate (ADP) into ATP. The ATP synthase cont ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ferredoxin
Ferredoxins (from Latin ''ferrum'': iron + redox, often abbreviated "fd") are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied to the "iron protein" first purified in 1962 by Mortenson, Valentine, and Carnahan from the anaerobic organism, anaerobic bacterium ''Clostridium pasteurianum''. Another redox protein, isolated from spinach chloroplasts, was termed "chloroplast ferredoxin". The chloroplast ferredoxin is involved in both cyclic and non-cyclic photophosphorylation reactions of photosynthesis. In non-cyclic photophosphorylation, ferredoxin is the last electron acceptor thus reducing the enzyme NADP+ reductase. It accepts electrons produced from sunlight-Electron excitation, excited chlorophyll and transfers them to the enzyme ferredoxin: NADP+ oxidoreductase . Ferredoxins are small proteins containing iron and sulfur atoms organized as iron–sulfur clusters ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ferredoxin—NADP(+) Reductase
In enzymology, a ferredoxin-NADP reductase () abbreviated FNR, is an enzyme that catalyzes the chemical reaction :2 reduced ferredoxin + NADP + H \rightleftharpoons 2 oxidized ferredoxin + NADPH The 3 substrates of this enzyme are reduced ferredoxin, NADP, and H, whereas its two products are oxidized ferredoxin and NADPH. It has a flavin cofactor, FAD. This enzyme belongs to the family of oxidoreductases, that use iron-sulfur proteins as electron donors and NAD or NADP as electron acceptors. This enzyme participates in photosynthesis. FNR provides a major source of NADPH for photosynthetic organisms. Nomenclature The systematic name of this enzyme class is ferredoxin:NADP oxidoreductase. Other names in common use include: * adrenodoxin reductase, * ferredoxin-NADP reductase, * ferredoxin-NADP oxidoreductase, * ferredoxin-nicotinamide adenine dinucleotide phosphate reductase, * ferredoxin-nicotinamide-adenine dinucleotide phosphate (oxidized), reductase * ferredoxin-TP ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thylakoid Lumen
Thylakoids are membrane-bound compartments inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as grana (singular: ''granum''). Grana are connected by intergranal or stromal thylakoids, which join granum stacks together as a single functional compartment. In thylakoid membranes, chlorophyll pigments are found in packets called quantasomes. Each quantasome contains 230 to 250 chlorophyll molecules. Etymology The word ''Thylakoid'' comes from the Greek word ''thylakos'' or ''θύλακος'', meaning "sac" or "pouch". Thus, ''thylakoid'' means "sac-like" or "pouch-like". Structure Thylakoids are membrane-bound structures embedded in the chloroplast stroma. A stack of thylakoids is called a granum and resembles a stack of coins. Membrane The thylakoid membrane is the site of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stroma (fluid)
Stroma, in botany, refers to the colorless fluid surrounding the grana within the chloroplast. Within the stroma are grana (stacks of thylakoid), the sub-organelles where photosynthesis is started before the chemical changes are completed in the stroma. Kramer & Scott ''flower'' iv. 80 1979 Photosynthesis occurs in two stages. In the first stage, ''light-dependent reactions'' capture the energy of light and use it to make the energy-storage molecules ATP and NADPH. During the second stage, the ''light-independent reactions'' use these products to fix carbon by capturing and reducing carbon dioxide. The series of biochemical redox reactions which take place in the stroma are collectively called the Calvin cycle or ''light-independent reactions''. There are three phases: carbon fixation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration. The stroma is also the location of chloroplast DNA and chloroplast ribosomes, and thus also the location of molecul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photolysis
Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by absorption of light or photons. It is defined as the interaction of one or more photons with one target molecule that dissociates into two fragments. Here, “light” is broadly defined as radiation spanning the vacuum ultraviolet (VUV), ultraviolet (UV), visible, and infrared (IR) regions of the electromagnetic spectrum. To break covalent bonds, photon energies corresponding to visible, UV, or VUV light are typically required, whereas IR photons may be sufficiently energetic to detach ligands from coordination complexes or to fragment supramolecular complexes. Photolysis in photosynthesis Photolysis is part of the light-dependent reaction, light phase, photochemical phase, or Hill reaction of photosynthesis. The general reaction of photosynthetic photolysis can be given in terms of photons as: :\ce + 2 \text \longri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pheophytin
Pheophytin or phaeophytin is a chemical compound that serves as the first electron carrier intermediate in the electron transfer pathway of Photosystem II (PS II) in plants, and the type II photosynthetic reaction center (RC P870) found in purple bacteria. In both PS II and RC P870, light drives electrons from the reaction center through pheophytin, which then passes the electrons to a quinone (QA) in RC P870 and RC P680. The overall mechanisms, roles, and purposes of the pheophytin molecules in the two transport chains are analogous to each other. Structure In biochemical terms, pheophytin is a chlorophyll molecule lacking a central Mg2+ ion. It can be produced from chlorophyll by treatment with a weak acid, producing a dark bluish waxy pigment. The probable etymology comes from this description, with ''pheo'' meaning ''dusky'' and ''phyt'' meaning ''vegetation''. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
P680
P680, or photosystem II primary donor, is the reaction-center chlorophyll ''a'' molecular dimer associated with photosystem II in plants, algae, and cyanobacteria, and central to oxygenic photosynthesis. Etymology Its name is derived from the word “pigment” (P) and the presence of a major bleaching band centered around 680-685 nm in the flash-induced absorbance difference spectra of P680/ P680+•.Shigeru Itoh, S; Iwaki, M; Tomo, T; Satoh, K (1996). Dibromothymoquinone (DBMIB) replaces the function of QA at 77 K in the isolated photosystem II reaction center (Dl-D2-cytochrome 6559) complex: Difference spectrum of the P680+ (DBMIB") state. Plant Cell Physiol. 37(6): 833-839. Components The structure of P680 consists of a hetero dimer of two distinct chlorophyll molecules, referred to as P and P. This “special pair” forms an excitonic dimer that functions as a single unit, excited by light energy as if they were a single molecule. Action and function Excitat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plastocyanin
Plastocyanin is a copper-containing protein that mediates electron-transfer. It is found in a variety of plants, where it participates in photosynthesis. The protein is a prototype of the blue copper proteins, a family of intensely blue-colored metalloproteins. Specifically, it falls into the group of small type I blue copper proteins called "cupredoxins". Function In photosynthesis, plastocyanin functions as an electron transfer agent between cytochrome f of the cytochrome ''b''6''f'' complex from photosystem II and P700+ from photosystem I. Cytochrome ''b''6''f'' complex and P700+ are both membrane-bound proteins with exposed residues on the lumen-side of the thylakoid membrane of chloroplasts. Cytochrome f acts as an electron donor while P700+ accepts electrons from reduced plastocyanin. Structure The copper site in plastocyanin, with the four amino acids that bind the metal labelled. Plastocyanin was the first of the blue copper proteins to be characterised by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
