1.
Heme
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Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group, these are known as hemoproteins. Hemoproteins have diverse functions including the transportation of diatomic gases, chemical catalysis, diatomic gas detection. The heme iron serves as a source or sink of electrons during electron transfer or redox chemistry, in peroxidase reactions, the porphyrin molecule also serves as an electron source. In the transportation or detection of gases, the gas binds to the heme iron. During the detection of gases, the binding of the gas ligand to the heme iron induces conformational changes in the surrounding protein. Hemoproteins achieve their remarkable diversity by modifying the environment of the heme macrocycle within the protein matrix. For example, the ability of hemoglobin to effectively deliver oxygen to tissues is due to amino acid residues located near the heme molecule. Hemoglobin reversibly binds to oxygen in the lungs when the pH is high, when the situation is reversed, hemoglobin will release oxygen into the tissues. This phenomenon, which states that hemoglobins oxygen binding affinity is inversely proportional to both acidity and concentration of carbon dioxide, is known as the Bohr effect. There are several biologically important kinds of heme, The most common type is heme B, other important types include heme A, isolated hemes are commonly designated by capital letters while hemes bound to proteins are designated by lower case letters. Cytochrome a refers to the heme A in specific combination with membrane protein forming a portion of cytochrome c oxidase, the following carbon numbering system of porphyrins is an older numbering used by biochemists and not the 1–24 numbering system recommended by IUPAC which is shown in the table above. Heme l is the derivative of heme B which is attached to the protein of lactoperoxidase, eosinophil peroxidase. The addition of peroxide with the glutamyl-375 and aspartyl-225 of lactoperoxidase forms ester bonds between amino acid residues and the heme 1- and 5-methyl groups, respectively. Similar ester bonds with two methyl groups are thought to form in eosinophil and thyroid peroxidases. Heme l is one important characteristic of animal peroxidases, plant peroxidases incorporate heme B, lactoperoxidase and eosinophil peroxidase are protective enzymes responsible for the destruction of invading bacteria and virus. Thyroid peroxidase is the enzyme catalyzing the biosynthesis of the important thyroid hormones, because lactoperoxidase destroys invading organisms in the lungs and excrement, it is thought to be an important protective enzyme. Heme m is the derivative of heme B covalently bound at the site of myeloperoxidase. Heme m contains the two ester bonds at the heme 1- and 5-methyls as in heme l found in other mammalian peroxidases, myeloperoxidase is present in mammalian neutrophils and is responsible for the destruction of invading bacteria and viruse
2.
Protein
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Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, a linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide, short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides, or sometimes oligopeptides. The individual amino acid residues are bonded together by peptide bonds, the sequence of amino acid residues in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the code specifies 20 standard amino acids, however. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors, proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes. Once formed, proteins only exist for a period of time and are then degraded and recycled by the cells machinery through the process of protein turnover. A proteins lifespan is measured in terms of its half-life and covers a wide range and they can exist for minutes or years with an average lifespan of 1–2 days in mammalian cells. Abnormal and or misfolded proteins are degraded more rapidly due to being targeted for destruction or due to being unstable. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms, many proteins are enzymes that catalyse biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized, digestion breaks the proteins down for use in the metabolism. Methods commonly used to study structure and function include immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance. Most proteins consist of linear polymers built from series of up to 20 different L-α-amino acids, all proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group, a carboxyl group, and a variable side chain are bonded. Only proline differs from this structure as it contains an unusual ring to the N-end amine group. The amino acids in a chain are linked by peptide bonds. Once linked in the chain, an individual amino acid is called a residue, and the linked series of carbon, nitrogen. The peptide bond has two forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are roughly coplanar
3.
Ferrous
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Ferrous, in chemistry, indicates a divalent iron compound, as opposed to ferric, which indicates a trivalent iron compound. Outside chemistry, ferrous is a used to indicate the presence of iron. The word is derived from the Latin word ferrum, Ferrous metals include steel and pig iron and alloys of iron with other metals. Manipulation of atom-to-atom relationships between iron, carbon, and various alloying elements establishes the specific properties of ferrous metals, the term non-ferrous is used to indicate metals other than iron and alloys that do not contain an appreciable amount of iron. Ferromagnetism Steelmaking Ferrous metal recycling Iron oxide Ferrous chloride Iron bromide
4.
Ferric
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Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an number of +3. On the other hand, ferrous refers to iron with oxidation number of +2, iron is usually the most stable form of iron in air, as illustrated by the pervasiveness of rust, an insoluble iron-containing material. The word ferric is derived from the Latin word ferrum for iron, examples include iron-sulfur clusters, oxyhemoglobin, ferritin, and the cytochromes. The bioavailability of iron is of great interest because all forms of life require iron. Iron-deficiency anemia illustrates the problems resulting from low iron intake, many foods contain soluble iron compounds and are therefore necessary for good nutrition. The low bioavailability of iron affects all forms of life, bacteria secrete iron-attracting agents called siderophores that form soluble compounds of iron that can be reabsorbed into the cell and used in building iron-containing metalloproteins. The impact of increasing the bioavailability of iron was famously demonstrated by an experiment where an area of the ocean surface was sprayed with iron salts. After several days, the phytoplankton within the treated area bloomed to such an extent that the effect was visible from outer space and this fertilizing process has been proposed as a means to mitigate the carbon dioxide content of the atmosphere. Ferric iron mitigates the eutrophication of lakes by reducing the bioavailability of phosphorus in the water, mitigation arises because ferric phosphate is insoluble. Like iron, phosphate is often a limiting nutrient, and its reduction in concentration from solution limits the growth of algae, in water, ferric iron forms compounds that are often insoluble, at least near neutral pH. A salt of ferric iron hydrolyzes water and produces iron oxide-hydroxides while contributing hydrogen ions to the solution, in contrast, typical Na+ salts dissolve in water without lowering the pH. Aluminium behaves similarly to ferric ion, rust, a mixture of ferric hydroxide compounds, illustrates the low solubility of ferric ions in water. Various reagents cause rust to dissolve even at neutral pH and these ligands include EDTA, which forms a chelate complex with the ion, displacing the hydroxide and oxide ligands that comprise rust. For this reason, EDTA is often used to iron deposits or to deliver soluble iron in fertilizers. Citrate also solubilizes ferric ion at neutral pH, although its complexes are less stable than those of EDTA, Ferric iron is a d5 center, meaning that the metal has five valence electrons in the 3d orbital shell. The magnetism of ferric compounds is determined by these five electrons. Usually ferric ions are surrounded by six ligands arranged in octahedron, sometimes three and sometimes as many as seven ligands are observed
5.
Cytochrome c oxidase
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The enzyme cytochrome c oxidase or Complex IV, EC1.9.3.1 is a large transmembrane protein complex found in bacteria and the mitochondrion of eukaryotes. It is the last enzyme in the electron transport chain of mitochondria located in the mitochondrial membrane. It receives an electron from each of four cytochrome c molecules, the complex is a large integral membrane protein composed of several metal prosthetic sites and 14 protein subunits in mammals. In mammals, eleven subunits are nuclear in origin, and three are synthesized in the mitochondria, the complex contains two hemes, a cytochrome a and cytochrome a3, and two copper centers, the CuA and CuB centers. In fact, the cytochrome a3 and CuB form a center that is the site of oxygen reduction. The reduced CuA binuclear center now passes an electron on to cytochrome a, the two metal ions in this binuclear center are 4.5 Å apart and coordinate a hydroxide ion in the fully oxidized state. Crystallographic studies of cytochrome c oxidase show an unusual post-translational modification, linking C6 of Tyr and it plays a vital role in enabling the cytochrome a3- CuB binuclear center to accept four electrons in reducing molecular oxygen to water. The mechanism of reduction was formerly thought to involve a peroxide intermediate, however, the currently accepted mechanism involves a rapid four-electron reduction involving immediate oxygen-oxygen bond cleavage, avoiding any intermediate likely to form superoxide. COX subunits are encoded in both the nuclear and mitochondrial genomes, the three subunits that form the COX catalytic core are encoded in the mitochondrial genome. Hemes and cofactors are inserted into subunits I & II, subunits I and IV initiate assembly. Different subunits may associate to form intermediates that later bind to other subunits to form the COX complex. In post-assembly modifications, COX will form a homodimer, both dimers are connected by a cardiolipin molecule, which has been found to play a key role in stabilization of the holoenzyme complex. The dissociation of subunits VIIa and III in conjunction with the removal of cardiolipin results in loss of enzyme activity. Subunits encoded in the genome are known to play a role in enzyme dimerization. Mutations to these subunits eliminate COX function, assembly is known to occur in at least three distinct rate-determining steps. The products of these steps have been found, though specific subunit compositions have not been determined, synthesis and assembly of COX subunits I, II, and III are facilitated by translational activators, which interact with the 5’ untranslated regions of mitochondrial mRNA transcripts. Translational activators are encoded in the nucleus, the hydroxide ligand is protonated and lost as water, creating a void between the metals that is filled by O2. The oxygen is reduced, with two electrons coming from the Fe2+cytochrome a3, which is converted to the ferryl oxo form
6.
Cytochrome P450
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Cytochromes P450 are proteins of the superfamily containing heme as a cofactor and, therefore, are hemoproteins. CYPs use a variety of small and large molecules as substrates in enzymatic reactions and they are, in general, the terminal oxidase enzymes in electron transfer chains, broadly categorized as P450-containing systems. The term P450 is derived from the peak at the wavelength of the absorption maximum of the enzyme when it is in the reduced state. CYP enzymes have been identified in all kingdoms of life, animals, plants, fungi, protists, bacteria, archaea, however, they are not omnipresent, for example, they have not been found in Escherichia coli. More than 200,000 distinct CYP proteins are known, most CYPs require a protein partner to deliver one or more electrons to reduce the iron. Cytochrome b5 can also contribute reducing power to this system after being reduced by cytochrome b5 reductase, mitochondrial P450 systems, which employ adrenodoxin reductase and adrenodoxin to transfer electrons from NADPH to P450. Bacterial P450 systems, which employ a ferredoxin reductase and a ferredoxin to transfer electrons to P450, cYB5R/cyb5/P450 systems, in which both electrons required by the CYP come from cytochrome b5. FMN/Fd/P450 systems, originally found in Rhodococcus species, in which a FMN-domain-containing reductase is fused to the CYP, P450 only systems, which do not require external reducing power. Notable ones include thromboxane synthase, prostacyclin synthase, and CYP74A, the most common reaction catalyzed by cytochromes P450 is a monooxygenase reaction, e. g. The convention is to italicise the name referring to the gene. For example, CYP2E1 is the gene encodes the enzyme CYP2E1—one of the enzymes involved in paracetamol metabolism. The CYP nomenclature is the naming convention, although occasionally CYP450 or CYP450 is used synonymously. However, some gene or enzyme names for CYPs may differ from this nomenclature, denoting the catalytic activity, examples include CYP5A1, thromboxane A2 synthase, abbreviated to TBXAS1, and CYP51A1, lanosterol 14-α-demethylase, sometimes unofficially abbreviated to LDM according to its substrate and activity. The current nomenclature guidelines suggest that members of new CYP families share at least 40% amino acid identity, there are nomenclature committees that assign and track both base gene names and allele names. The active site of cytochrome P450 contains a heme-iron center, the iron is tethered to the protein via a cysteine thiolate ligand. This cysteine and several flanking residues are conserved in known CYPs and have the formal PROSITE signature consensus pattern - - x - - - - - C - -. Because of the vast variety of reactions catalyzed by CYPs, the activities and properties of the many CYPs differ in many aspects. In general, the P450 catalytic cycle proceeds as follows, Substrate binds in proximity to the heme group, Substrate binding induces electron transfer from NADH via cytochrome P450 reductase or another associated reductase
7.
David Keilin
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David Keilin FRS was an entomologist, among other things. He was born in Moscow in 1887 and his family returned to Warsaw early in his youth and he did not attend school until age ten due to ill health and asthma. Only seven years later, in 1904, he enrolled in the University of Liège and he later studied at Magdalene College, Cambridge, and became a British citizen. He made extensive contributions to entomology and parasitology during his career and he published thirty-nine papers between 1914 and 1923 on the reproduction of lice, the life-cycle of the horse bot-fly, the respiratory adaptations in fly larvae, and other subjects. He is most known for his research and rediscovery of cytochrome in the 1920s and it had been discovered by C. A. MacMunn in 1884, but that discovery had been forgotten or misunderstood. Keilin was elected a Fellow of the Royal Society in 1926 and he won its Royal Medal in 1939 and its Copley Medal in 1951
8.
Electron
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The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, the electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the include a intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant. As it is a fermion, no two electrons can occupy the same state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of particles and waves, they can collide with other particles and can be diffracted like light. Since an electron has charge, it has an electric field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law, electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields, special telescopes can detect electron plasma in outer space. Electrons are involved in applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors. Interactions involving electrons with other particles are of interest in fields such as chemistry. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms, ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of a quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge electron in 1891, electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of isotopes and in high-energy collisions. The antiparticle of the electron is called the positron, it is identical to the electron except that it carries electrical, when an electron collides with a positron, both particles can be totally annihilated, producing gamma ray photons. The ancient Greeks noticed that amber attracted small objects when rubbed with fur, along with lightning, this phenomenon is one of humanitys earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον
9.
Iron
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Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series and it is by mass the most common element on Earth, forming much of Earths outer and inner core. It is the fourth most common element in the Earths crust, like the other group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen, fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, Iron metal has been used since ancient times, although copper alloys, which have lower melting temperatures, were used even earlier in human history. Pure iron is soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon. A certain proportion of carbon steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron alloys formed with metals are by far the most common industrial metals because they have a great range of desirable properties. Iron chemical compounds have many uses, Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens, among its organometallic compounds is ferrocene, the first sandwich compound discovered. Iron plays an important role in biology, forming complexes with oxygen in hemoglobin and myoglobin. Iron is also the metal at the site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants. A human male of average height has about 4 grams of iron in his body and this iron is distributed throughout the body in hemoglobin, tissues, muscles, bone marrow, blood proteins, enzymes, ferritin, hemosiderin, and transport in plasma. The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test, the data on iron is so consistent that it is often used to calibrate measurements or to compare tests. An increase in the content will cause a significant increase in the hardness. Maximum hardness of 65 Rc is achieved with a 0. 6% carbon content, because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium. Because of its significance for planetary cores, the properties of iron at high pressures and temperatures have also been studied extensively
10.
Redox
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Redox is a chemical reaction in which the oxidation states of atoms are changed. Any such reaction involves both a process and a complementary oxidation process, two key concepts involved with electron transfer processes. Redox reactions include all chemical reactions in which atoms have their oxidation state changed, in general, the chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. It can be explained in terms, Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom. Reduction is the gain of electrons or a decrease in state by a molecule, atom. As an example, during the combustion of wood, oxygen from the air is reduced, the reaction can occur relatively slowly, as in the case of rust, or more quickly, as in the case of fire. Redox is a portmanteau of reduction and oxidation, the word oxidation originally implied reaction with oxygen to form an oxide, since dioxygen was historically the first recognized oxidizing agent. Later, the term was expanded to encompass oxygen-like substances that accomplished parallel chemical reactions, ultimately, the meaning was generalized to include all processes involving loss of electrons. The word reduction originally referred to the loss in weight upon heating a metallic ore such as an oxide to extract the metal. In other words, ore was reduced to metal, antoine Lavoisier showed that this loss of weight was due to the loss of oxygen as a gas. Later, scientists realized that the atom gains electrons in this process. The meaning of reduction then became generalized to all processes involving gain of electrons. Even though reduction seems counter-intuitive when speaking of the gain of electrons, it help to think of reduction as the loss of oxygen. Since electrons are charged, it is also helpful to think of this as reduction in electrical charge. The electrochemist John Bockris has used the words electronation and deelectronation to describe reduction and oxidation processes respectively when they occur at electrodes and these words are analogous to protonation and deprotonation, but they have not been widely adopted by chemists. The term hydrogenation could be used instead of reduction, since hydrogen is the agent in a large number of reactions. But, unlike oxidation, which has been generalized beyond its root element, the word redox was first used in 1928. The processes of oxidation and reduction occur simultaneously and cannot happen independently of one another, the oxidation alone and the reduction alone are each called a half-reaction, because two half-reactions always occur together to form a whole reaction
11.
Oxidative phosphorylation
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Oxidative phosphorylation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing energy which is used to reform 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 an efficient way of releasing energy. During oxidative phosphorylation, electrons are transferred from electron donors to electron acceptors such as oxygen and these redox reactions release energy, which is used to form ATP. 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 mitochondrial membrane. This generates potential energy in the form of a pH gradient and this store of energy is tapped by allowing protons to flow back across the membrane and down this gradient, through a large enzyme called ATP synthase, this process is known as chemiosmosis. This enzyme uses energy to generate ATP from adenosine diphosphate. This reaction is driven by the flow, which forces the rotation of a part of the enzyme. The enzymes carrying out this metabolic pathway are also the target of many drugs and this means one cannot occur without the other. These enzymes are like a battery, as they work to drive current through the circuit. The movement of protons creates an electrochemical gradient across the membrane and it has two components, a difference in proton concentration and a difference in electric potential, with the N-side having a negative charge. ATP synthase releases this energy by completing the circuit and allowing protons to flow down the electrochemical gradient. The electrochemical gradient drives the rotation of part of the enzymes structure, inversely, chloroplasts operate mainly on ΔpH. However, they require a small membrane potential for the kinetics of ATP synthesis. At least in the case of the fusobacterium P. modestum it drives the counter-rotation of subunits a and c of the FO motor of ATP synthase, the amount of energy released by oxidative phosphorylation is high, compared with the amount produced by anaerobic fermentation. These ATP yields are theoretical maximum values, in practice, some protons leak across the membrane, the electron transport chain carries both protons and electrons, passing electrons from donors to acceptors, and transporting protons across a membrane. These processes use both soluble and protein-bound transfer molecules, in mitochondria, electrons are transferred within the intermembrane space by the water-soluble electron transfer protein cytochrome c
12.
Complex (chemistry)
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Many metal-containing compounds, especially those of transition metals, are coordination complexes. A coordination complex whose centre is an atom is called a metal complex. Coordination complexes are so pervasive that their structures and reactions are described in many ways, the atom within a ligand that is bonded to the central metal atom or ion is called the donor atom. In a typical complex, an ion is bonded to several donor atoms. A polydentate ligand is a molecule or ion that bonds to the atom through several of the ligands atoms. These complexes are called chelate complexes, the formation of complexes is called chelation, complexation. The central atom or ion, together with all ligands comprise the coordination sphere, the central atoms or ion and the donor atoms comprise the first coordination sphere. Coordination refers to the covalent bonds between the ligands and the central atom. Originally, a complex implied a reversible association of molecules, atoms, as applied to coordination chemistry, this meaning has evolved. Some metal complexes are formed virtually irreversibly and many are bound together by bonds that are quite strong, the number of donor atoms attached to the central atom or ion is called the coordination number. The most common coordination numbers are 2,4 and especially 6, for example, the cobalt hexahydrate ion or the hexaaquacobalt ion 2+, is a hydrated-complex ion that consists of six water molecules attached to a metal ion Co. The oxidation state and the number reflect the number of bonds formed between the metal ion and the ligands in the complex ion. However the coordination number of Pt2+ 2is 4 since it has two ligands, which contain four donor atoms in total. Coordination complexes have been known since the beginning of modern chemistry, early well-known coordination complexes include dyes such as Prussian blue. Their properties were first well understood in the late 1800s, following the 1869 work of Christian Wilhelm Blomstrand, Blomstrand developed what has come to be known as the complex ion chain theory. The theory claimed that the reason coordination complexes form is because in solution and he compared this effect to the way that various carbohydrate chains form. Following this theory, Danish scientist Sophus Mads Jorgensen made improvements to it and it was not until 1893 that the most widely accepted version of the theory today was published by Alfred Werner. Werner’s work included two important changes to the Blomstrand theory, the first was that Werner described the two different ion possibilities in terms of location in the coordination sphere
13.
Cofactor (biochemistry)
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A cofactor is a non-protein chemical compound or metallic ion that is required for a proteins biological activity to happen. These proteins are enzymes, and cofactors can be considered helper molecules that assist in biochemical transformations. A coenzyme that is tightly or even covalently bound is termed a prosthetic group, the two subcategories under coenzyme are cosubstrates and prosthetic groups. Cosubstrates are transiently bound to the protein and will be released at some point, the prosthetic groups, on the other hand, are bound permanently to the protein. Both of them have the function, which is to facilitate the reaction of enzymes. Additionally, some sources also limit the use of the cofactor to inorganic substances. An inactive enzyme without the cofactor is called an apoenzyme, while the enzyme with cofactor is called a holoenzyme. Some enzymes or enzyme complexes require several cofactors, organic cofactors are often vitamins or made from vitamins. Many contain the nucleotide adenosine monophosphate as part of their structures, such as ATP, coenzyme A, FAD and this common structure may reflect a common evolutionary origin as part of ribozymes in an ancient RNA world. It has been suggested that the AMP part of the molecule can be considered to be a kind of handle by which the enzyme can grasp the coenzyme to switch it between different catalytic centers. Cofactors can be divided into two groups, organic cofactors, such as flavin or heme, and inorganic cofactors, such as the metal ions Mg2+, Cu+, Mn2+. Organic cofactors are sometimes divided into coenzymes and prosthetic groups. The term coenzyme refers specifically to enzymes and, as such, on the other hand, prosthetic group emphasizes the nature of the binding of a cofactor to a protein and, thus, refers to a structural property. Different sources give different definitions of coenzymes, cofactors. It should be noted that terms are often used loosely. However, the author could not arrive at a single all-encompassing definition of a coenzyme, the study of these cofactors falls under the area of bioinorganic chemistry. In nutrition, the list of essential trace elements reflects their role as cofactors, in humans this list commonly includes iron, magnesium, manganese, cobalt, copper, zinc, and molybdenum. Although chromium deficiency causes impaired glucose tolerance, no human enzyme that uses this metal as a cofactor has been identified, iodine is also an essential trace element, but this element is used as part of the structure of thyroid hormones rather than as an enzyme cofactor
14.
Adenosine triphosphate
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Adenosine triphosphate is a nucleotide, also called a nucleoside triphosphate, is a small molecule used in cells as a coenzyme. It is often referred to as the unit of currency of intracellular energy transfer. ATP transports chemical energy within cells for metabolism, most cellular functions need energy in order to be carried out, synthesis of proteins, synthesis of membranes, movement of the cell, cellular division, transport of various solutes etc. The ATP is the molecule that carries energy to the place where the energy is needed, when ATP breaks into ADP and Pi, the breakdown of the last covalent link of phosphate liberates energy that is used in reactions where it is needed. Substrate-level phosphorylation, oxidative phosphorylation in cellular respiration, and photophosphorylation in photosynthesis are three mechanisms of ATP biosynthesis. Metabolic processes that use ATP as an energy source convert it back into its precursors, ATP is therefore continuously recycled in organisms, the human body, which on average contains only 250 grams of ATP, turns over its own body weight equivalent in ATP each day. ATP is used as a substrate in signal transduction pathways by kinases that phosphorylate proteins and it is also used by adenylate cyclase, which uses ATP to produce the second messenger molecule cyclic AMP. The ratio between ATP and AMP is used as a way for a cell to sense how much energy is available and control the metabolic pathways that produce and consume ATP. Apart from its roles in signaling and energy metabolism, ATP is also incorporated into nucleic acids by polymerases in the process of transcription, ATP is the neurotransmitter believed to signal the sense of taste. The structure of this consists of a purine base attached by the 9′ nitrogen atom to the 1′ carbon atom of a pentose sugar. Three phosphate groups are attached at the 5′ carbon atom of the pentose sugar and it is the addition and removal of these phosphate groups that inter-convert ATP, ADP and AMP. When ATP is used in DNA synthesis, the sugar is first converted to deoxyribose by ribonucleotide reductase. ATP was discovered in 1929 by Karl Lohmann, and independently by Cyrus Fiske and Yellapragada Subbarow of Harvard Medical School and it was proposed to be the intermediary molecule between energy-yielding and energy-requiring reactions in cells by Fritz Albert Lipmann in 1941. It was first artificially synthesized by Alexander Todd in 1948, ATP consists of adenosine – composed of an adenine ring and a ribose sugar – and three phosphate groups. The phosphoryl groups, starting with the group closest to the ribose, are referred to as the alpha, beta, consequently, it is closely related to the adenosine nucleotide, a monomer of RNA. ATP is highly soluble in water and is stable in solutions between pH6.8 and 7.4, but is rapidly hydrolysed at extreme pH. Consequently, ATP is best stored as an anhydrous salt, ATP is an unstable molecule in unbuffered water, in which it hydrolyses to ADP and phosphate. This is because the strength of the bonds between the groups in ATP is less than the strength of the hydrogen bonds, between its products, and water
15.
Flagellum
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A flagellum is a lash-like appendage that protrudes from the cell body of certain prokaryotic and eukaryotic cells. The word flagellum in Latin means whip, the primary role of the flagellum is locomotion, but it also often has function as a sensory organelle, being sensitive to chemicals and temperatures outside the cell. Flagella are organelles defined by function rather than structure, large differences occur between different types of flagella, the prokaryotic and eukaryotic flagella differ greatly in protein composition, structure, and mechanism of propulsion. However, both can be used for swimming, an example of a flagellated bacterium is the ulcer-causing Helicobacter pylori, which uses multiple flagella to propel itself through the mucus lining to reach the stomach epithelium. An example of a eukaryotic cell is the mammalian sperm cell. Eukaryotic flagella are structurally identical to eukaryotic cilia, although distinctions are made according to function and/or length. Fimbriae and pili are also thin appendages, but have different functions and are usually smaller, three types of flagella have so far been distinguished, bacterial, archaeal, and eukaryotic. The main differences among these three types are, Bacterial flagella are helical filaments, each with a motor at its base which can turn clockwise or counterclockwise. They provide two of several kinds of bacterial motility, archaeal flagella are superficially similar to bacterial flagella, but are different in many details and considered non-homologous. Eukaryotic flagella—those of animal, plant, and protist cells—are complex cellular projections that lash back, eukaryotic flagella are classed along with eukaryotic motile cilia as undulipodia to emphasize their distinctive wavy appendage role in cellular function or motility. Primary cilia are immotile, and are not undulipodia, they have a structurally different 9+0 axoneme rather than the 9+2 axoneme found in both flagella and motile cilia undulipodia, the bacterial flagellum is made up of the protein flagellin. Its shape is a 20-nanometer-thick hollow tube and it is helical and has a sharp bend just outside the outer membrane, this hook allows the axis of the helix to point directly away from the cell. A shaft runs between the hook and the body, passing through protein rings in the cells membrane that act as bearings. Gram-positive organisms have two of these basal body rings, one in the layer and one in the plasma membrane. The filament ends with a capping protein, the flagellar filament is the long, helical screw that propels the bacterium when rotated by the motor, through the hook. Each protofilament is a series of protein chains. However, Campylobacter jejuni has seven protofilaments, the basal body has several traits in common with some types of secretory pores, such as the hollow, rod-like plug in their centers extending out through the plasma membrane. The bacterial flagellum is driven by an engine made up of protein
16.
Spectroscopy
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Spectroscopy /spɛkˈtrɒskəpi/ is the study of the interaction between matter and electromagnetic radiation. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, later the concept was expanded greatly to include any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data is represented by an emission spectrum, a plot of the response of interest as a function of wavelength or frequency. Spectroscopy and spectrography are terms used to refer to the measurement of radiation intensity as a function of wavelength and are used to describe experimental spectroscopic methods. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers, daily observations of color can be related to spectroscopy. Neon lighting is an application of atomic spectroscopy. Neon and other noble gases have characteristic emission frequencies, neon lamps use collision of electrons with the gas to excite these emissions. Inks, dyes and paints include chemical compounds selected for their characteristics in order to generate specific colors. A commonly encountered molecular spectrum is that of nitrogen dioxide, gaseous nitrogen dioxide has a characteristic red absorption feature, and this gives air polluted with nitrogen dioxide a reddish-brown color. Rayleigh scattering is a spectroscopic scattering phenomenon that accounts for the color of the sky, Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms, Spectroscopy is also used in astronomy and remote sensing on earth. The measured spectra are used to determine the composition and physical properties of astronomical objects. One of the concepts in spectroscopy is a resonance and its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums, mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. A plot of amplitude vs. excitation frequency will have a peak centered at the resonance frequency and this plot is one type of spectrum, with the peak often referred to as a spectral line, and most spectral lines have a similar appearance. In quantum mechanical systems, the resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon. The coupling of the two states is strongest when the energy of the matches the energy difference between the two states. The energy of a photon is related to its frequency by E = h ν where h is Plancks constant, spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states
17.
Cytochrome
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Cytochromes are iron containing hemeproteins central to which are heme groups that are primarily responsible for the generation of ATP via electron transport. They are found either as monomeric proteins or as subunits of enzymatic complexes that catalyze redox reactions. Cytochromes were initially described in 1884 by MacMunn as respiratory pigments, the ultra-violet to visible spectroscopic signatures of hemes are still used to identify heme type from the reduced bis-pyridine-ligated state, i. e. the pyridine hemochrome method. The heme group is a highly conjugated ring system surrounding a metal ion, for many cytochromes, the metal ion present is that of iron, which interconverts between Fe2+ and Fe3+ states. Cytochromes are, thus, capable of performing oxidation and reduction, because the cytochromes are held within membranes in an organized way, the redox reactions are carried out in the proper sequence for maximum efficiency. The resulting transmembrane proton gradient is used to generate ATP, which is the chemical energy currency of life. ATP is consumed to drive cellular processes that require energy, several kinds of cytochrome exist and can be distinguished by spectroscopy, exact structure of the heme group, inhibitor sensitivity, and reduction potential. Three types of cytochrome are distinguished by their groups, The definition of cytochrome c is not defined in terms of the heme group. There is no cytochrome e, but there is a cytochrome f and these enzymes are primarily involved in steroidogenesis and detoxification. Scripps Database of Metalloproteins Cytochromes at the US National Library of Medicine Medical Subject Headings
18.
Cytochrome b
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Cytochrome b is a protein found in the mitochondria of eukaryotic cells. It functions as part of the transport chain and is the main subunit of transmembrane cytochrome bc1. In the mitochondrion of eukaryotes and in prokaryotes, cytochrome b is a component of respiratory chain complex III — also known as the bc1 complex or ubiquinol-cytochrome c reductase. In plant chloroplasts and cyanobacteria, there is a protein, cytochrome b6. These complexes are involved in transport, the pumping of protons to create a proton-motive force. This proton gradient is used for the generation of ATP and these complexes play a vital role in cells. Cytochrome b/b6 is a membrane protein of approximately 400 amino acid residues that probably has 8 transmembrane segments. In plants and cyanobacteria, cytochrome b6 consists of two subunits encoded by the petB and petD genes, cytochrome b/b6 non-covalently binds two heme groups, known as b562 and b566. Four conserved histidine residues are postulated to be the ligands of the atoms of these two heme groups. Cytochrome b is used as a region of mitochondrial DNA for determining phylogenetic relationships between organisms, due to its sequence variability. It is considered to be most useful in determining relationships within families, mutations in cytochrome b primarily result in exercise intolerance in human patients, though more rare, severe multi-system pathologies have also been reported. Single-point mutations in cytochrome b of Plasmodium falciparum and P. berghei are associated with resistance to the anti-malarial drug atovaquone
19.
Cytochrome d
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Cytochrome d is a protein that belongs to the Cytochrome family. Concretely, it is an enzyme – a protein that catalyses a chemical reaction, Cytochrome d is also known as cytochrome/heme a2. It is found in plenty of aerobic bacteria, especially when it has grown with an oxygen supply. The bacteria species in which it is commonly found are Escherichia coli. It is a protein, which means that is compound of two subunits. At the same time, cytochrome d is part of the cytochrome bd-I terminal oxidase which catalyse the two electron oxidation of ubiquinol and this process is an oxidative phosphorylation that oxidizes the ubiquinol-8 to ubiquinone. The chemical reaction followed by this process is, Ubiquinol-8 + O2 = Ubiquinone-8 + H2O By a similar reaction, it catalyses the reduction of oxygen to water. Generally, in protein complexes, it gives a band of approximately 636 nm or 638 nm. If it is oxidized, the band has a length of 636 nm, and it is commonly associated to certain prosthetic groups when found in multiple subunit complexes. Detecting cytochrome d as Fe pyridine alkaline hemachrome is very difficult because the stability under these conditions is limited, if cytochrome d is pulled out of the protein complex and placed in ether containing from 1 to 5 % of HCl, it gives a different absorption band. The cytochrome d complex from E. coli is a found in the bacterial cytoplasmic bilayer. Cytochrome d presents two subunits in this organism, which were analyzed by genetic methods including alkaline phosphatase gene fusions and these fusions were done in vivo and in vitro, which implied the utilization of the transposon TnphoA in the in vivo method. The in vitro method consisted on a construction, in the end,48 isolated fusions helped to determine the activities of the specific alkaline phosphatase in cells. The basis of the 2D models for each subunit was developed thanks to the data of these fusions and this basis also defines how these subunits fold in the E. coli membrane, specially in the inner one. Azotobacter vinelandii is a nitrogen-fixing bacteria which is known by its high rate among aerobic organisms. Some physiological studies postulate that cytochrome d functions as an oxidase in the membranes of this organism. The studies characterized the different genes in the two subunits, a very extensive homology with CydA and CydB of the E. coli was found in these studies. Cytochrome bd is a tri-heme oxidase as it is compound by cytochromes b558, b595 and its main function is the reduction of O2 to H2O
20.
Chelation
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Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a ligand and a single central atom. Usually these ligands are organic compounds, and are called chelants, chelators, chelating agents, the chelate effect is the enhanced affinity of chelating ligands for a metal ion compared to the affinity of a collection of similar nonchelating ligands for the same metal. Consider the two equilibria, in solution, between the copper ion, Cu2+ and ethylenediamine on the one hand and methylamine, MeNH2 on the other. In the bidentate ligand ethylenediamine forms a complex with the copper ion. Chelation results in the formation of a five-membered CuC2N2 ring, the thermodynamic approach to describing the chelate effect considers the equilibrium constant for the reaction, the larger the equilibrium constant, the higher the concentration of the complex. Electrical charges have been omitted for simplicity of notation, the square brackets indicate concentration, and the subscripts to the stability constants, β, indicate the stoichiometry of the complex. Δ H ⊖ is the enthalpy change of the reaction. Since the enthalpy should be approximately the same for the two reactions, the difference between the two stability constants is due to the effects of entropy. In equation there are two particles on the left and one on the right, whereas in equation there are three particles on the left and one on the right. This difference means that less entropy of disorder is lost when the complex is formed than when the complex with monodentate ligands is formed. This is one of the factors contributing to the entropy difference, other factors include solvation changes and ring formation. Some experimental data to illustrate the effect are shown in the following table, other explanations, including that of Schwarzenbach, are discussed in Greenwood and Earnshaw. Numerous biomolecules exhibit the ability to dissolve certain metal cations, thus, proteins, polysaccharides, and polynucleic acids are excellent polydentate ligands for many metal ions. Organic compounds such as the amino acids glutamic acid and histidine, organic diacids such as malate, in addition to these adventitious chelators, several biomolecules are specifically produced to bind certain metals. Virtually all metalloenzymes feature metals that are chelated, usually to peptides or cofactors, such chelating agents include the porphyrin rings in hemoglobin and chlorophyll. Many microbial species produce pigments that serve as chelating agents. For example, species of Pseudomonas are known to secrete pyochelin, enterobactin, produced by E. coli, is the strongest chelating agent known
21.
Cytochrome c
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The cytochrome complex, or cyt c is a small hemeprotein found loosely associated with the inner membrane of the mitochondrion. It belongs to the cytochrome c family of proteins, cytochrome c is highly water-soluble, unlike other cytochromes, and is an essential component of the electron transport chain, where it carries one electron. It is capable of undergoing oxidation and reduction, but does not bind oxygen and it transfers electrons between Complexes III and IV. In humans, cytochrome c is encoded by the CYCS gene, cytochrome c is a highly conserved protein across the spectrum of species, found in plants, animals, and many unicellular organisms. This, along with its size, makes it useful in studies of cladistics. The cytochrome c molecule has been studied for the glimpse it gives into evolutionary biology and its primary structure consists of a chain of about 100 amino acids. Many higher-order organisms possess a chain of 104 amino acids, the sequences of cytochrome c in humans is identical to that of chimpanzees, but differs more from that of horses. Its amino acid sequence is conserved in eukaryotes, differing by only a few residues. In more than thirty species,34 of the 104 amino acids are conserved, for example, human cytochrome oxidase reacts with wheat cytochrome c, in vitro, this is true for all pairs of species tested. In addition the redox potential of +0.25 volts is the same in all cytochrome c molecules studied, all cytochrome c proteins contain a characteristic CXXCH amino acid motif that binds heme. However, there are four classes of cytochrome c, each possessing a different fold, in 1991 R. P. Ambler recognized four classes of cytochrome c, Class I includes the lowspin soluble cytochrome c of mitochondria and bacteria. It has the heme-attachment site towards the N terminus of histidine, Class II includes the highspin cytochrome c. It has the heme-attachment site closed to the N terminus of histidine, Class III comprises the low redox potential multiple-heme cytochromes. The heme c groups are structurally and functionally nonequivalent and present different redox potentials in the range 0 to −400 mV, Class IV was originally created to hold the complex proteins that have other prosthetic groups as well as heme c. One of the properties of heme c, which allows cytochrome c to have variety of functions, is its ability to have different reduction potentials in nature. This property determines the kinetics and thermodynamics of a transfer reaction. The dipole moment has an important role in orienting proteins to the proper directions, the dipole moment of cytochrome c is a result from a cluster of negatively charged amino acid side chains at the back of the enzyme. Despite variations in the number of bound heme groups and variations in sequence, for examples, vertebrate cytochromes c all have dipole moment of approximately 320 debye while cytochromes c of plants and insects have dipole moment of approximately 340 debye
22.
Cytochrome f
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Cytochrome f is the largest subunit of cytochrome b6f complex. In its structure and functions, the cytochrome b6f complex bears extensive analogy to the cytochrome bc1 complex of mitochondria, cytochrome f plays a role analogous to that of cytochrome c1, in spite of their different structures. The 3D structure of Brassica rapa cyt f has been determined, the lumen-side segment of cyt f includes two structural domains, a small one above a larger one that, in turn, is on top of the attachment to the membrane domain. The large domain consists of an anti-parallel beta-sandwich and a short haem-binding peptide, the small domain is inserted between beta-strands F and G of the large domain and is an all-beta domain. The haem nestles between two short helices at the N terminus of cyt f, within the second helix is the sequence motif for the c-type cytochromes, CxxCH, which is covalently attached to the haem through thioether bonds to Cys-21 and Cys-24. His-25 is the fifth iron ligand. The sixth haem iron ligand is the group of Tyr-1 in the first helix. Cyt f has an network of water molecules that may function as a proton wire. The water chain appears to be a feature of cyt f. The unfinished story of cytochrome f, huang, D. Tae, G. S. Everly, R. M. Heymann, J. B. Cheng, R. H. Baker, T. S. & Smith, structural aspects of the cytochrome b6f complex, structure of the lumen-side domain of cytochrome f. J. Bioenerg. Cytochrome f at the US National Library of Medicine Medical Subject Headings This article incorporates text from the public domain Pfam and InterPro IPR002325
23.
Mitochondrion
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The mitochondrion is a double membrane-bound organelle found in all eukaryotic organisms. Some cells in multicellular organisms may however lack them. A number of organisms, such as microsporidia, parabasalids. To date, only one eukaryote, Monocercomonoides, is known to have completely lost its mitochondria, the word mitochondrion comes from the Greek μίτος, mitos, thread, and χονδρίον, chondrion, granule or grain-like. Mitochondria generate most of the supply of adenosine triphosphate, used as a source of chemical energy. Mitochondria are commonly between 0.75 and 3 μm in diameter but vary considerably in size and structure, unless specifically stained, they are not visible. Mitochondrial biogenesis is in turn temporally coordinated with these cellular processes, Mitochondria have been implicated in several human diseases, including mitochondrial disorders, cardiac dysfunction, heart failure and autism. The number of mitochondria in a cell can vary widely by organism, tissue, for instance, red blood cells have no mitochondria, whereas liver cells can have more than 2000, The organelle is composed of compartments that carry out specialized functions. These compartments or regions include the outer membrane, the space, the inner membrane. Although most of a cells DNA is contained in the cell nucleus, mitochondrial proteins vary depending on the tissue and the species. In humans,615 distinct types of protein have been identified from cardiac mitochondria, the mitochondrial proteome is thought to be dynamically regulated. The first observations of structures that probably represented mitochondria were published in the 1840s. Richard Altmann, in 1890, established them as cell organelles, the term mitochondria was coined by Carl Benda in 1898. Leonor Michaelis discovered that Janus green can be used as a stain for mitochondria in 1900. Benjamin F. Kingsbury, in 1912, first related them with cell respiration, in 1913, particles from extracts of guinea-pig liver were linked to respiration by Otto Heinrich Warburg, which he called grana. Warburg and Heinrich Otto Wieland, who had postulated a similar particle mechanism. It was not until 1925, when David Keilin discovered cytochromes, in the following years, the mechanism behind cellular respiration was further elaborated, although its link to the mitochondria was not known. The introduction of tissue fractionation by Albert Claude allowed mitochondria to be isolated from other cell fractions, in 1946, he concluded that cytochrome oxidase and other enzymes responsible for the respiratory chain were isolated to the mitchondria
24.
Chloroplast
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Chloroplasts /ˈklɔːrəˌplæsts, -plɑːsts/ are organelles, specialized subunits, in plant and algal cells. Their discovery inside plant cells is usually credited to Julius von Sachs and they then use the ATP and NADPH to make organic molecules from carbon dioxide in a process known as the Calvin cycle. Chloroplasts carry out a number of functions, including fatty acid synthesis, much amino acid synthesis. The number of chloroplasts per cell varies from one, in algae, up to 100 in plants like Arabidopsis. A chloroplast is a type of known as a plastid. Other plastid types, such as the leucoplast and the chromoplast, contain little chlorophyll, chloroplasts are highly dynamic—they circulate and are moved around within plant cells, and occasionally pinch in two to reproduce. Their behavior is influenced by environmental factors like light color. Chloroplasts, like mitochondria, contain their own DNA, which is thought to be inherited from their ancestor—a photosynthetic cyanobacterium that was engulfed by a eukaryotic cell. Chloroplasts cannot be made by the plant cell and must be inherited by each cell during cell division. With one exception, all chloroplasts can probably be traced back to a single endosymbiotic event, despite this, chloroplasts can be found in an extremely wide set of organisms, some not even directly related to each other—a consequence of many secondary and even tertiary endosymbiotic events. The word chloroplast is derived from the Greek words chloros, which means green, and plastes, the first definitive description of a chloroplast was given by Hugo von Mohl in 1837 as discrete bodies within the green plant cell. In 1883, A. F. W. Schimper would name these bodies as chloroplastids, in 1884, Eduard Strasburger adopted the term chloroplasts. Chloroplasts are one of many types of organelles in the plant cell and they are considered to have originated from cyanobacteria through endosymbiosis—when a eukaryotic cell engulfed a photosynthesizing cyanobacterium that became a permanent resident in the cell. Mitochondria are thought to have come from an event, where an aerobic prokaryote was engulfed. This origin of chloroplasts was first suggested by the Russian biologist Konstantin Mereschkowski in 1905 after Andreas Schimper observed in 1883 that chloroplasts closely resemble cyanobacteria, chloroplasts are only found in plants, algae, and the amoeboid Paulinella chromatophora. Cyanobacteria are considered the ancestors of chloroplasts and they are sometimes called blue-green algae even though they are prokaryotes. They are a phylum of bacteria capable of carrying out photosynthesis. Cyanobacteria also contain a cell wall, which is thicker than in other gram-negative bacteria
25.
Electron transport chain
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This creates an electrochemical proton gradient that drives the synthesis of adenosine triphosphate, a molecule that stores energy chemically in the form of highly strained bonds. The molecules of the chain include peptides, enzymes, and others, 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 mitochondrial membrane where it serves as the site of oxidative phosphorylation through the use of ATP synthase. It is also found in the membrane of the chloroplast in photosynthetic eukaryotes. In bacteria, the transport chain is located in their cell membrane. In chloroplasts, light drives the conversion of water to oxygen, 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 electron leakage to oxygen, generating superoxide. The electron transport chain consists of a spatially separated series of reactions in which electrons are transferred from a donor molecule to an acceptor molecule. The underlying force driving these reactions is the Gibbs free energy of the reactants and products, the Gibbs free energy is the energy available to do work. Any reaction that decreases the overall Gibbs free energy of a system is thermodynamically spontaneous, the function of the electron transport chain is to produce a transmembrane proton electrochemical gradient as a result of the redox reactions. If protons flow back through the membrane, they enable mechanical work, ATP synthase, an enzyme highly conserved among all domains of life, converts this mechanical work into chemical energy by producing ATP, which powers most cellular reactions. A small amount of ATP is available from substrate-level phosphorylation, for example, 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 cycle, fatty acid oxidation. At the mitochondrial membrane, electrons from NADH and FADH2 pass through the electron transport chain to oxygen. The electron transport chain comprises a series of electron donors and acceptors. The entire process is called oxidative phosphorylation, since ADP is phosphorylated to ATP using the energy of hydrogen oxidation in many steps and this proton gradient is largely but not exclusively responsible for the mitochondrial membrane potential. It allows ATP synthase to use the flow of H+ through the back into the matrix to generate ATP from adenosine diphosphate. Complex I accepts electrons from the Krebs cycle electron carrier nicotinamide adenine dinucleotide, and passes them to coenzyme Q, Q passes electrons to complex III, which passes them to cytochrome c
26.
Cytochrome C1
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Cytochrome C1 is a protein encoded by the CYC1 gene. Cytochrome is a subunit of the cytochrome b-c1 complex, which accepts electrons from Rieske protein. It is formed in the cytosol and targeted to the intermembrane space. Cytochrome c1 belongs to the cytochrome c family of proteins, cytochrome C1 plays a role in the electron transfer during oxidative phosphorylation. As an iron-sulfur protein approaches the b-c1 complex, it accepts an electron from the b subunit. There, the electron carried by the protein is transferred to the heme carried by cytochrome c1. This electron is transferred to a heme carried by cytochrome c. This creates a reduced species of cytochrome c, which separates from the complex and moves to the last enzyme in the electron transport chain. There are orthologs of CYC1 in 137 known organisms, mutations in the CYC1 gene are associated with mitochondrial complex III deficiency nuclear type 6. The disease symptoms include early childhood onset of severe lactic acidosis and ketoacidosis, insulin-responsive hyperglycemia is also present, but psychomotor development appears normal. Mutation of CYC1 was observed to cause instability in the cytochrome b-c1 complex, mitochondrial complex III deficiency nuclear type 6 is autosomal recessive. Cytochrome c1 at the US National Library of Medicine Medical Subject Headings This article incorporates text from the public domain Pfam and InterPro IPR002326
27.
Cytochrome b6f complex
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The reaction is analogous to the reaction catalyzed by cytochrome bc1 of the mitochondrial electron transport chain. The cytochrome b6f complex is a dimer, with each monomer composed of eight subunits, the total molecular weight is 217 kDa. The crystal structure of cytochrome b6f complexes from Chlamydomonas reinhardtii, Mastigocladus laminosus, the core of the complex is structurally similar to cytochrome bc1 core. Cytochrome b6 and subunit IV are homologous to cytochrome b and the Rieske iron-sulfur proteins of the two complexes are homologous, however, cytochrome f and cytochrome c1 are not homologous. Cytochrome b6f contains seven prosthetic groups, four are found in both cytochrome b6f and bc1, the c-type heme of cytochrome c1 and f, the two b-type hemes in bc1 and b6f, and the cluster of the Rieske protein. Three unique prosthetic groups are found in cytochrome b6f, chlorophyll a, β-carotene, electron transport via cytochrome b6f is responsible for creating the proton gradient that drives the synthesis of ATP in chloroplasts. In a separate reaction, the cytochrome b6f complex plays a role in cyclic photophosphorylation. This cycle results in the creation of a gradient by cytochrome b6f. It has also shown that this cycle is essential for photosynthesis. The p-side quinol deprotonation-oxidation reactions within the cytochrome b6f complex have been implicated in the generation of reactive oxygen species, plastoquinone acts as the electron carrier, transferring its two electrons to high- and low-potential electron transport chains via a mechanism called electron bifurcation. First half of Q cycle QH2 binds to the p side of the complex. It is oxidized to a semiquinone by the center and releases two protons to the thylakoid lumen. The reduced iron-sulfur center transfers its electron through cytochrome f to Pc, in the low-potential ETC, SQ transfers its electron to heme bp of cytochrome b6. Heme bp then transfers the electron to heme bn, heme bn reduces Q with one electron to form SQ. Second half of Q cycle A second QH2 binds to the complex, in the high-potential ETC, one electron reduces another oxidized Pc. In the low-potential ETC, the electron from heme bn is transferred to SQ, the oxidized Q and the reduced QH2 that has been regenerated diffuse into the membrane. In contrast to Complex III, cytochrome b6f catalyzes another electron transfer reaction that is central to cyclic photophosphorylation, the electron from ferredoxin is transferred to plastoquinone and then the cytochrome b6f complex to reduce plastocyanin, which is reoxidized by P700 in Photosystem I. The exact mechanism for how plastoquinone is reduced by ferredoxin is still under investigation, one proposal is that there exists a ferredoxin, plastoquinone-reductase or an NADP dehydrogenase
28.
Sodium dithionite
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Sodium dithionite is a white crystalline powder with a weak sulfurous odor. It is the salt of dithionous acid. Although it is stable under most conditions, it will decompose in hot water, in one anhydrous form, the dithionite ion has C2 geometry, almost eclipsed with a 16° O-S-S-O torsional angle. In the dihydrated form, the anion has a shorter S-S bond length. The weak S-S bond causes the dithionite anion to dissociate into the − radical anion in aqueous solution and it is also observed that 35S undergoes rapid exchange between S2O42− and SO2 in neutral or acidic solution, consistent with the weak S-S bond in the anion. Sodium dithionite is stable when dry, but is oxidized by air when in solution. Anhydrous is a crystal with slightly sulfuric odor. It is soluble in water and slightly soluble in ethanol, dihydrate is a columnar crystal, and it is so unstable that it easily dehydrates to anhydrous and is easily oxidized by oxygen in the air. Anhydrous gradually decomposes to sodium sulfate and sulfur dioxide above 90 °C in the air, in absence of air, it decomposes quickly above 150 °C to sodium sulfite, sodium thiosulfate, sulfur dioxide and trace amount of sulfur. Powdered anhydrous sodium dithionite with an amount of water may ignite in air by the heat of decomposition. In absence of air, it decomposes slowly. An aqueous solution of sodium dithionite is acidic and decomposes to sodium thiosulfate, the reaction rate increases with increasing temperature. In addition, the rate is higher under stronger acidity,2 Na2S2O4 + H2O → Na2S2O3 +2 NaHSO3 In presence of oxygen, it decomposes to sodium bisulfate and sodium bisulfite. Na2S2O4 + O2 + H2O → NaHSO4 + NaHSO3 Sodium bisulfate and sodium bisulfite decrease the pH, sulfur dioxide is formed under strongly acidic conditions. 2 H2S2O4 →3 SO2 + S +2 H2O3 H2S2O4 →5 SO2 + H2S +2 H2O On the other hand, alkali solution is stable and it has strong reducing properties and decomposes to sulfurous acid and sulfide. Some ketones are also reduced under similar conditions and this compound is a water-soluble salt, and can be used as a reducing agent in aqueous solutions. The reduction properties of sodium dithionite also eliminate excess dye, residual oxide, Sodium dithionite can also be used for water treatment, gas purification, cleaning, and stripping. It can also be used in processes as a sulfonating agent or a sodium ion source
29.
Steroidogenesis
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A steroid is an organic compound with four rings arranged in a specific configuration. Examples include the dietary lipid cholesterol, the sex hormones estradiol and testosterone, the steroid core structure is composed of seventeen carbon atoms, bonded in four fused rings, three six-member cyclohexane rings and one five-member cyclopentane ring. Steroids vary by the groups attached to this four-ring core. Sterols are forms of steroids with a group at position three and a skeleton derived from cholestane. They can also vary more markedly by changes to the ring structure, hundreds of steroids are found in plants, animals and fungi. All steroids are manufactured in cells from the sterols lanosterol or cycloartenol, lanosterol and cycloartenol are derived from the cyclization of the triterpene squalene. The three cyclohexane rings form the skeleton of a derivative of phenanthrene. The D ring has a cyclopentane structure, when the two methyl groups and eight carbon side chains are present, the steroid is said to have a cholestane framework. The following are some categories of steroids. In eukaryotes, steroids are found in fungi, animals, animal steroids include compounds of vertebrate and insect origin, the latter including ecdysteroids such as ecdysterone. Steroid hormones include, Sex hormones, which influence sex differences and these include androgens, estrogens, and progestagens. In popular use, the term often refers to anabolic steroids. Plant steroids include steroidal alkaloids found in Solanaceae, the phytosterols, in prokaryotes, biosynthetic pathways exist for the tetracyclic steroid framework – where its origin from eukaryotes is conjectured – and the more-common pentacyclic triterpinoid hopanoid framework. One example of how MeSH performs this classification is available at the Wikipedia MeSH catalog, examples of this classification include, The gonane is the parent 17-carbon tetracyclic hydrocarbon molecule with no alkyl sidechains. Secosteroids are a subclass of steroidal compounds resulting, biosynthetically or conceptually, major secosteroid subclasses are defined by the steroid carbon atoms where this scission has taken place. Norsteroids and homosteroids are structural subclasses of steroids formed from biosynthetic steps, the former involves enzymic ring expansion-contraction reactions, and the latter is accomplished or through ring closures of acyclic precursors with more ring atoms than the parent steroid framework. Combinations of these alterations are known in nature. Ingestion of these C-nor-D-homosteroids results in defects in lambs, cyclopia from cyclopamine
30.
International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
31.
OCLC
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The Online Computer Library Center is a US-based nonprofit cooperative organization dedicated to the public purposes of furthering access to the worlds information and reducing information costs. It was founded in 1967 as the Ohio College Library Center, OCLC and its member libraries cooperatively produce and maintain WorldCat, the largest online public access catalog in the world. OCLC is funded mainly by the fees that libraries have to pay for its services, the group first met on July 5,1967 on the campus of the Ohio State University to sign the articles of incorporation for the nonprofit organization. The group hired Frederick G. Kilgour, a former Yale University medical school librarian, Kilgour wished to merge the latest information storage and retrieval system of the time, the computer, with the oldest, the library. The goal of network and database was to bring libraries together to cooperatively keep track of the worlds information in order to best serve researchers and scholars. The first library to do online cataloging through OCLC was the Alden Library at Ohio University on August 26,1971 and this was the first occurrence of online cataloging by any library worldwide. Membership in OCLC is based on use of services and contribution of data, between 1967 and 1977, OCLC membership was limited to institutions in Ohio, but in 1978, a new governance structure was established that allowed institutions from other states to join. In 2002, the structure was again modified to accommodate participation from outside the United States. As OCLC expanded services in the United States outside of Ohio, it relied on establishing strategic partnerships with networks, organizations that provided training, support, by 2008, there were 15 independent United States regional service providers. OCLC networks played a key role in OCLC governance, with networks electing delegates to serve on OCLC Members Council, in early 2009, OCLC negotiated new contracts with the former networks and opened a centralized support center. OCLC provides bibliographic, abstract and full-text information to anyone, OCLC and its member libraries cooperatively produce and maintain WorldCat—the OCLC Online Union Catalog, the largest online public access catalog in the world. WorldCat has holding records from public and private libraries worldwide. org, in October 2005, the OCLC technical staff began a wiki project, WikiD, allowing readers to add commentary and structured-field information associated with any WorldCat record. The Online Computer Library Center acquired the trademark and copyrights associated with the Dewey Decimal Classification System when it bought Forest Press in 1988, a browser for books with their Dewey Decimal Classifications was available until July 2013, it was replaced by the Classify Service. S. The reference management service QuestionPoint provides libraries with tools to communicate with users and this around-the-clock reference service is provided by a cooperative of participating global libraries. OCLC has produced cards for members since 1971 with its shared online catalog. OCLC commercially sells software, e. g. CONTENTdm for managing digital collections, OCLC has been conducting research for the library community for more than 30 years. In accordance with its mission, OCLC makes its research outcomes known through various publications and these publications, including journal articles, reports, newsletters, and presentations, are available through the organizations website. The most recent publications are displayed first, and all archived resources, membership Reports – A number of significant reports on topics ranging from virtual reference in libraries to perceptions about library funding
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JSTOR
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JSTOR is a digital library founded in 1995. Originally containing digitized back issues of journals, it now also includes books and primary sources. It provides full-text searches of almost 2,000 journals, more than 8,000 institutions in more than 160 countries have access to JSTOR, most access is by subscription, but some older public domain content is freely available to anyone. William G. Bowen, president of Princeton University from 1972 to 1988, JSTOR originally was conceived as a solution to one of the problems faced by libraries, especially research and university libraries, due to the increasing number of academic journals in existence. Most libraries found it prohibitively expensive in terms of cost and space to maintain a collection of journals. By digitizing many journal titles, JSTOR allowed libraries to outsource the storage of journals with the confidence that they would remain available long-term, online access and full-text search ability improved access dramatically. Bowen initially considered using CD-ROMs for distribution, JSTOR was initiated in 1995 at seven different library sites, and originally encompassed ten economics and history journals. JSTOR access improved based on feedback from its sites. Special software was put in place to make pictures and graphs clear, with the success of this limited project, Bowen and Kevin Guthrie, then-president of JSTOR, wanted to expand the number of participating journals. They met with representatives of the Royal Society of London and an agreement was made to digitize the Philosophical Transactions of the Royal Society dating from its beginning in 1665, the work of adding these volumes to JSTOR was completed by December 2000. The Andrew W. Mellon Foundation funded JSTOR initially, until January 2009 JSTOR operated as an independent, self-sustaining nonprofit organization with offices in New York City and in Ann Arbor, Michigan. JSTOR content is provided by more than 900 publishers, the database contains more than 1,900 journal titles, in more than 50 disciplines. Each object is identified by an integer value, starting at 1. In addition to the site, the JSTOR labs group operates an open service that allows access to the contents of the archives for the purposes of corpus analysis at its Data for Research service. This site offers a facility with graphical indication of the article coverage. Users may create focused sets of articles and then request a dataset containing word and n-gram frequencies and they are notified when the dataset is ready and may download it in either XML or CSV formats. The service does not offer full-text, although academics may request that from JSTOR, JSTOR Plant Science is available in addition to the main site. The materials on JSTOR Plant Science are contributed through the Global Plants Initiative and are only to JSTOR
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PubMed Identifier
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PubMed is a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine at the National Institutes of Health maintains the database as part of the Entrez system of information retrieval, from 1971 to 1997, MEDLINE online access to the MEDLARS Online computerized database primarily had been through institutional facilities, such as university libraries. PubMed, first released in January 1996, ushered in the era of private, free, home-, the PubMed system was offered free to the public in June 1997, when MEDLINE searches via the Web were demonstrated, in a ceremony, by Vice President Al Gore. Information about the journals indexed in MEDLINE, and available through PubMed, is found in the NLM Catalog. As of 5 January 2017, PubMed has more than 26.8 million records going back to 1966, selectively to the year 1865, and very selectively to 1809, about 500,000 new records are added each year. As of the date,13.1 million of PubMeds records are listed with their abstracts. In 2016, NLM changed the system so that publishers will be able to directly correct typos. Simple searches on PubMed can be carried out by entering key aspects of a subject into PubMeds search window, when a journal article is indexed, numerous article parameters are extracted and stored as structured information. Such parameters are, Article Type, Secondary identifiers, Language, publication type parameter enables many special features. As these clinical girish can generate small sets of robust studies with considerable precision, since July 2005, the MEDLINE article indexing process extracts important identifiers from the article abstract and puts those in a field called Secondary Identifier. The secondary identifier field is to store numbers to various databases of molecular sequence data, gene expression or chemical compounds. For clinical trials, PubMed extracts trial IDs for the two largest trial registries, ClinicalTrials. gov and the International Standard Randomized Controlled Trial Number Register, a reference which is judged particularly relevant can be marked and related articles can be identified. If relevant, several studies can be selected and related articles to all of them can be generated using the Find related data option, the related articles are then listed in order of relatedness. To create these lists of related articles, PubMed compares words from the title and abstract of each citation, as well as the MeSH headings assigned, using a powerful word-weighted algorithm. The related articles function has been judged to be so precise that some researchers suggest it can be used instead of a full search, a strong feature of PubMed is its ability to automatically link to MeSH terms and subheadings. Examples would be, bad breath links to halitosis, heart attack to myocardial infarction, where appropriate, these MeSH terms are automatically expanded, that is, include more specific terms. Terms like nursing are automatically linked to Nursing or Nursing and this important feature makes PubMed searches automatically more sensitive and avoids false-negative hits by compensating for the diversity of medical terminology. The My NCBI area can be accessed from any computer with web-access, an earlier version of My NCBI was called PubMed Cubby
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International Standard Serial Number
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An International Standard Serial Number is an eight-digit serial number used to uniquely identify a serial publication. The ISSN is especially helpful in distinguishing between serials with the same title, ISSN are used in ordering, cataloging, interlibrary loans, and other practices in connection with serial literature. The ISSN system was first drafted as an International Organization for Standardization international standard in 1971, ISO subcommittee TC 46/SC9 is responsible for maintaining the standard. When a serial with the content is published in more than one media type. For example, many serials are published both in print and electronic media, the ISSN system refers to these types as print ISSN and electronic ISSN, respectively. The format of the ISSN is an eight digit code, divided by a hyphen into two four-digit numbers, as an integer number, it can be represented by the first seven digits. The last code digit, which may be 0-9 or an X, is a check digit. Formally, the form of the ISSN code can be expressed as follows, NNNN-NNNC where N is in the set, a digit character. The ISSN of the journal Hearing Research, for example, is 0378-5955, where the final 5 is the check digit, for calculations, an upper case X in the check digit position indicates a check digit of 10. To confirm the check digit, calculate the sum of all eight digits of the ISSN multiplied by its position in the number, the modulus 11 of the sum must be 0. There is an online ISSN checker that can validate an ISSN, ISSN codes are assigned by a network of ISSN National Centres, usually located at national libraries and coordinated by the ISSN International Centre based in Paris. The International Centre is an organization created in 1974 through an agreement between UNESCO and the French government. The International Centre maintains a database of all ISSNs assigned worldwide, at the end of 2016, the ISSN Register contained records for 1,943,572 items. ISSN and ISBN codes are similar in concept, where ISBNs are assigned to individual books, an ISBN might be assigned for particular issues of a serial, in addition to the ISSN code for the serial as a whole. An ISSN, unlike the ISBN code, is an identifier associated with a serial title. For this reason a new ISSN is assigned to a serial each time it undergoes a major title change, separate ISSNs are needed for serials in different media. Thus, the print and electronic versions of a serial need separate ISSNs. Also, a CD-ROM version and a web version of a serial require different ISSNs since two different media are involved, however, the same ISSN can be used for different file formats of the same online serial
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Hemeprotein
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A hemeprotein, or heme protein, is a metalloprotein containing a heme prosthetic group- a virginal compound that allows a protein to carry out several functions that it cannot do alone. Heme remains bound to the protein permanently, either covalently or noncovalently bound or both, the heme contains an oxidized iron atom, Fe2+ in the center of a highly hydrophobic, planar, porphyrin ring. The iron has six possible coordination bonds, the porphyrin ring has 4 nitrogen atoms that bind to the iron, leaving two other coordination positions of the iron available for bonding to the histidine of the protein and a divalent atom. Hemeproteins probably evolved to incorporate the iron contained within the protoporphyrin IX ring of heme into proteins. As it makes hemeproteins responsive to molecules that can bind divalent iron, oxygen, nitric oxide, carbon monoxide and hydrogen sulfide bind to the iron atom in heme proteins. Once bound to the heme groups, these molecules can modulate the activity/function of those hemeproteins. Therefore, when produced in biologic systems, these molecules are referred to as gasotransmitters. Because of their range of biological functions, the structural and functional characterizations of hemeproteins are the most studied classes of biomolecules. Data on heme protein structure and function has been aggregated into The Heme Protein Database, Hemeproteins have diverse biological functions including oxygen transport, which is completed via hemeproteins including hemoglobin, myoglobin, neuroglobin, cytoglobin and leghemoglobin. Catalysis occurs with hemeproteins cytochrome P450s, cytochrome c oxidase, ligninases and peroxidases, Hemeproteins also enable electron transfer as they form part of the electron transport chain. Cyctochrome a, cytochrome b and cytochrome c are responsible for electron transfer functions, the sensory system also relies on some hemeproteins including FixL, an oxygen sensor, CooA, a carbon monoxide sensor, and soluble guanylyl cyclase. Finally, the hemeprotein catalase aids in biological defense, hemoglobin and myoglobin are examples of hemeproteins that are essential in the storing and transports of oxygen in mammals. Hemoglobin is a protein that occurs in the red blood cell, whereas. Although they might differ in location and size, their function are similar, being hemeproteins, they both contain a heme prosthetic group. His-F8 of the myoglobin, also known as the proximal histidine, is bonded to the 5th coordination position of the iron. Oxygen interacts with the distal His by way of a hydrogen bond and it binds to the 6th coordination position of the iron, His-E7 of the myoglobin binds to the oxygen that is now covalently bonded to the iron. The same is true for hemoglobin, however, being a protein with four subunits, hemoglobin contains four units in total. Myoglobin and hemoglobin are globular proteins that serve to bind and deliver oxygen and these globins dramatically improve the concentration of molecular oxygen that can be dissolved in the biological fluids of vertebrates and some invertebrates
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Globin
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The globins are a superfamily of heme-containing globular proteins, involved in binding and/or transporting oxygen. These proteins all incorporate the globin fold, a series of eight alpha helical segments, two prominent members include myoglobin and hemoglobin. Both of these proteins reversibly bind oxygen via a prosthetic group. They are widely distributed in many organisms, globin superfamily members share a common three-dimensional fold. This globin fold typically consists of eight alpha helices, although some proteins have additional helix extensions at their termini, since the globin fold contains only helices, it is classified as an all-alpha protein fold. The globin fold is found in its namesake globin families as well as in phycocyanins, the globin fold was thus the first protein fold discovered. The eight helices of the globin fold core share significant nonlocal structure, the helices pack together at an average angle of about 50 degrees, significantly steeper than other helical packings such as the helix bundle. Globins evolved from an ancestor and can be divided into three groups, single-domain globins, and two types of chimeric globins, flavohaemoglobins and globin-coupled sensors. Bacteria have all three types of globins, while archaea lack flavohaemoglobins, and eukaryotes lack globin-coupled sensors, several functionally different haemoglobins can coexist in the same species. Eight globins are known to occur in vertebrates, androglobin, cytoglobin, globin E, globin X, globin Y, although the fold of the globin superfamily is highly evolutionarily conserved, the sequences that form the fold can have as low as 16% sequence identity. The most famous mutation in the fold is a change from glutamate to valine in one chain of the hemoglobin molecule. This mutation creates a patch on the protein surface that promotes intermolecular aggregation. Neuroglobin belongs to a branch of the family that diverged early in evolution. Cytoglobin, an oxygen sensor expressed in multiple tissues, erythrocruorin, highly cooperative extracellular respiratory proteins found in annelids and arthropods that are assembled from as many as 180 subunit into hexagonal bilayers. Leghaemoglobin, occurs in the nodules of leguminous plants, where it facilitates the diffusion of oxygen to symbiotic bacteriods in order to promote nitrogen fixation. Non-symbiotic haemoglobin, occurs in plants, and can be over-expressed in stressed plants. Flavohaemoglobins, chimeric, with an N-terminal globin domain and a C-terminal ferredoxin reductase-like NAD/FAD-binding domain, fHb provides protection against nitric oxide via its C-terminal domain, which transfers electrons to haem in the globin. They bind oxygen, and act to initiate a response or regulate gene expression
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Hemoglobin
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Hemoglobin in the blood carries oxygen from the respiratory organs to the rest of the body. There it releases the oxygen to permit aerobic respiration to provide energy to power the functions of the organism in the process called metabolism, in mammals, the protein makes up about 96% of the red blood cells dry content, and around 35% of the total content. Hemoglobin has a capacity of 1.34 mL O2 per gram. The mammalian hemoglobin molecule can bind up to four oxygen molecules, Hemoglobin is involved in the transport of other gases, It carries some of the bodys respiratory carbon dioxide as carbaminohemoglobin, in which CO2 is bound to the globin protein. The molecule also carries the important regulatory molecule nitric oxide bound to a globin protein thiol group, Hemoglobin is also found outside red blood cells and their progenitor lines. Other cells that contain hemoglobin include the A9 dopaminergic neurons in the substantia nigra, macrophages, alveolar cells, in these tissues, hemoglobin has a non-oxygen-carrying function as an antioxidant and a regulator of iron metabolism. Hemoglobin and hemoglobin-like molecules are found in many invertebrates, fungi. In these organisms, hemoglobins may carry oxygen, or they may act to transport and regulate other small molecules and ions such as carbon dioxide, nitric oxide, hydrogen sulfide and sulfide. In 1825 J. F. Engelhard discovered that the ratio of Fe to protein is identical in the hemoglobins of several species, from the known atomic mass of iron he calculated the molecular mass of hemoglobin to n ×16000, the first determination of a proteins molecular mass. This hasty conclusion drew a lot of ridicule at the time from scientists who could not believe that any molecule could be that big, gilbert Smithson Adair confirmed Engelhards results in 1925 by measuring the osmotic pressure of hemoglobin solutions. The oxygen-carrying protein hemoglobin was discovered by Hünefeld in 1840, hemoglobins reversible oxygenation was described a few years later by Felix Hoppe-Seyler. In 1959, Max Perutz determined the structure of myoglobin by X-ray crystallography. This work resulted in his sharing with John Kendrew the 1962 Nobel Prize in Chemistry, the role of hemoglobin in the blood was elucidated by French physiologist Claude Bernard. The name hemoglobin is derived from the heme and globin. Each heme group contains one iron atom, that can bind one oxygen molecule through ion-induced dipole forces, the most common type of hemoglobin in mammals contains four such subunits. Hemoglobin consists of subunits, and these proteins, in turn, are folded chains of a large number of different amino acids called polypeptides. The amino acid sequence of any polypeptide created by a cell is in turn determined by the stretches of DNA called genes, in all proteins, it is the amino acid sequence that determines the proteins chemical properties and function. There is more than one gene, in humans, hemoglobin A is coded for by the genes, HBA1, HBA2
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Chromosome 16 (human)
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Chromosome 16 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome, chromosome 16 spans about 90 million base pairs and represents just under 3% of the total DNA in cells. Identifying genes on each chromosome is an area of genetic research. Because researchers use different approaches to genome annotation their predictions of the number of genes on each chromosome varies, in January 2017, two estimates differed by 18%, with one estimate giving 1,920 genes, and the other estimate giving 2,256 genes. In February 2010, a new cause of obesity due to a microdeletion on chromosome 16 was announced and it may explain about 1% of obesity cases
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Hemoglobin, alpha 1
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Hemoglobin, alpha 1, also known as HBA1, is a hemoglobin protein that in humans is encoded by the HBA1 gene. The human alpha globin gene cluster located on chromosome 16 spans about 30 kb and includes seven loci, the alpha-2 and alpha-1 coding sequences are identical. These genes differ slightly over the 5 untranslated regions and the introns, alpha thalassemias result from deletions of each of the alpha genes as well as deletions of both HBA2 and HBA1, some nondeletion alpha thalassemias have also been reported. Hemoglobin, alpha 1 has been shown to interact with HBB, geneReviews/NCBI/NIH/UW entry on Alpha-Thalassemia OMIM etries on Alpha-Thalassemia
