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Photoinhibition
Photoinhibition is light-induced reduction in the photosynthetic capacity of a plant, alga, or cyanobacterium. Photosystem II (PSII) is more sensitive to light than the rest of the photosynthetic machinery, and most researchers define the term as light-induced damage to PSII. In living organisms, photoinhibited PSII centres are continuously repaired via degradation and synthesis of the D1 protein of the photosynthetic reaction center of PSII. Photoinhibition is also used in a wider sense, as dynamic photoinhibition, to describe all reactions that decrease the efficiency of photosynthesis when plants are exposed to light. History The first measurements of photoinhibition were published in 1956 by Bessel Kok. Even in the very first studies, it was obvious that plants have a repair mechanism that continuously repairs photoinhibitory damage. In 1966, Jones and Kok measured the action spectrum of photoinhibition and found that ultraviolet light is highly photoinhibitory. The visible-li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photoinhibition
Photoinhibition is light-induced reduction in the photosynthetic capacity of a plant, alga, or cyanobacterium. Photosystem II (PSII) is more sensitive to light than the rest of the photosynthetic machinery, and most researchers define the term as light-induced damage to PSII. In living organisms, photoinhibited PSII centres are continuously repaired via degradation and synthesis of the D1 protein of the photosynthetic reaction center of PSII. Photoinhibition is also used in a wider sense, as dynamic photoinhibition, to describe all reactions that decrease the efficiency of photosynthesis when plants are exposed to light. History The first measurements of photoinhibition were published in 1956 by Bessel Kok. Even in the very first studies, it was obvious that plants have a repair mechanism that continuously repairs photoinhibitory damage. In 1966, Jones and Kok measured the action spectrum of photoinhibition and found that ultraviolet light is highly photoinhibitory. The visible-li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in carbohydrate molecules, such as sugars and starches, which are synthesized from carbon dioxide and water – hence the name ''photosynthesis'', from the Greek ''phōs'' (), "light", and ''synthesis'' (), "putting together". Most plants, algae, and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs. Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies most of the energy necessary for life on Earth. Although photosynthesis is performed differently by different species, the process always begins when energy from light is absorbed by proteins called reaction centers that contain green chlorophyll (and other colored) pigments/chromoph ... [...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 laboratory sett ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rate Equation
In chemistry, the rate law or rate equation for a reaction is an equation that links the initial or forward reaction rate with the concentrations or pressures of the reactants and constant parameters (normally rate coefficients and partial reaction orders). For many reactions, the initial rate is given by a power law such as :v_0\; =\; k mathrmx mathrmy where and express the concentration of the species and usually in moles per liter (molarity, ). The exponents and are the partial ''orders of reaction'' for and and the ''overall'' reaction order is the sum of the exponents. These are often positive integers, but they may also be zero, fractional, or negative. The constant is the reaction rate constant or ''rate coefficient'' of the reaction. Its value may depend on conditions such as temperature, ionic strength, surface area of an adsorbent, or light irradiation. If the reaction goes to completion, the rate equation for the reaction rate v\; =\; k cex cey applies throug ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reactive Oxygen Species
In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. The reduction of molecular oxygen () produces superoxide (), which is the precursor to most other reactive oxygen species: :O2 + e^- -> \ ^\bullet O2- Dismutation of superoxide produces hydrogen peroxide (): :2 H+ + \ ^\bullet O2^- + \ ^\bullet O2^- -> H2O2 + O2 Hydrogen peroxide in turn may be partially reduced, thus forming hydroxide ions and hydroxyl radicals (), or fully reduced to water: :H2O2 + e^- -> HO^- + \ ^\bullet OH :2 H+ + 2 e- + H2O2 -> 2 H2O In a biological context, ROS are byproducts of the normal metabolism of oxygen. ROS have roles in cell signaling and homeostasis. ROS are intrinsic to cellular functioning, and are present at low and stationary levels in normal cells. In plants, ROS are involved in metabolic processes related to photoprotection and toleran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protein Synthesis
Protein biosynthesis (or protein synthesis) is a core biological process, occurring inside Cell (biology), cells, homeostasis, balancing the loss of cellular proteins (via Proteolysis, degradation or Protein targeting, export) through the production of new proteins. Proteins perform a number of critical functions as enzymes, structural proteins or hormones. Protein synthesis is a very similar process for both prokaryotes and eukaryotes but there are some distinct differences. Protein synthesis can be divided broadly into two phases - Transcription (biology), transcription and Translation (biology), translation. During transcription, a section of DNA encoding a protein, known as a gene, is converted into a template molecule called messenger RNA (mRNA). This conversion is carried out by enzymes, known as RNA polymerases, in the cell nucleus, nucleus of the cell. In eukaryotes, this mRNA is initially produced in a premature form (Primary transcript, pre-mRNA) which undergoes post-tra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 lipid bilayer, where the hydrophobic tails are usually found. Plastoquinones are very structurally similar to ubiquinone, or coenzyme Q10, differing by the length of the isoprenyl side chain, replacement of the methoxy groups with methyl groups, and removal of the methyl group in the 2 position on the quinone. Like ubiquinone, it can come in several oxidation states: p ... [...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 c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Iron–sulfur Protein
Iron–sulfur proteins (or iron–sulphur proteins in British spelling) are proteins characterized by the presence of iron–sulfur clusters containing sulfide-linked di-, tri-, and tetrairon centers in variable oxidation states. Iron–sulfur clusters are found in a variety of metalloproteins, such as the ferredoxins, as well as NADH dehydrogenase, hydrogenases, coenzyme Q – cytochrome c reductase, succinate – coenzyme Q reductase and nitrogenase. Iron–sulfur clusters are best known for their role in the oxidation-reduction reactions of electron transport in mitochondria and chloroplasts. Both Complex I and Complex II of oxidative phosphorylation have multiple Fe–S clusters. They have many other functions including catalysis as illustrated by aconitase, generation of radicals as illustrated by SAM-dependent enzymes, and as sulfur donors in the biosynthesis of lipoic acid and biotin. Additionally, some Fe–S proteins regulate gene expression. Fe–S proteins are vulner ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photoinitiator
A photoinitiator is a molecule that creates reactive species (free radicals, cations or anions) when exposed to radiation (UV or visible). Synthetic photoinitiators are key components in photopolymers (for example, photo-curable coatings, adhesives and dental restoratives). Some small molecules in the atmosphere can also act as photoinitiators by decomposing to give free radicals (in photochemical smog). For instance, nitrogen dioxide (NO2) is produced in large quantities by gasoline-burning internal combustion engines. NO2 in the troposphere gives smog its brown coloration and catalyzes production of toxic ground-level ozone (O3). Molecular oxygen (O2) also serves as a photoinitiator in the stratosphere, breaking down into atomic oxygen and combining with O2 in order to form the ozone in the ozone layer. Reactions Photoinitators can create reactive species by different pathways including photodissociation and electron transfer. As an example of dissociation, hydrogen peroxide c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lincomycin
Lincomycin is a lincosamide antibiotic that comes from the actinomycete ''Streptomyces lincolnensis''. A related compound, clindamycin, is derived from lincomycin by using thionyl chloride to replace the 7-hydroxy group with a chlorine atom with inversion of chirality. It was released for medical use in September 1964. Uses Although similar in antibacterial spectrum and mechanism of action to macrolides, lincomycin is also effective against other organisms including actinomycetes and some species of '' Mycoplasma'' and ''Plasmodium''. However, because of its adverse effects and toxicity, it is rarely used today and reserved for patients allergic to penicillin or where bacteria have developed resistance. Clinical pharmacology Intramuscular administration of a single dose of 600 mg of Lincomycin produces average peak serum levels of 11.6 µg/mL at 60 min, and maintains therapeutic levels for 17 h to 20 h, for most susceptible gram-positive organis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always move at the speed of light in vacuum, (or about ). The photon belongs to the class of bosons. As with other elementary particles, photons are best explained by quantum mechanics and exhibit wave–particle duality, their behavior featuring properties of both waves and particles. The modern photon concept originated during the first two decades of the 20th century with the work of Albert Einstein, who built upon the research of Max Planck. While trying to explain how matter and electromagnetic radiation could be in thermal equilibrium with one another, Planck proposed that the energy stored within a material object should be regarded as composed of an integer number of discrete, equal-sized parts. To explain the photoelectric effect, Eins ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
