Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+. The free energy released in this process is used to form the high-energy molecules ATP and NADH. Glycolysis is a sequence of ten enzyme-catalyzed reactions. Most monosaccharides, such as fructose and galactose, can be converted to one of these intermediates; the intermediates may be directly useful. For example, the intermediate dihydroxyacetone phosphate is a source of the glycerol that combines with fatty acids to form fat. Glycolysis is an oxygen-independent metabolic pathway; the wide occurrence of glycolysis indicates. Indeed, the reactions that constitute glycolysis and its parallel pathway, the pentose phosphate pathway, occur metal-catalyzed under the oxygen-free conditions of the Archean oceans in the absence of enzymes. In most organisms, glycolysis occurs in the cytosol; the most common type of glycolysis is the Embden–Meyerhof–Parnas, discovered by Gustav Embden, Otto Meyerhof, Jakub Karol Parnas.
Glycolysis refers to other pathways, such as the Entner–Doudoroff pathway and various heterofermentative and homofermentative pathways. However, the discussion here will be limited to the Embden–Meyerhof–Parnas pathway; the glycolysis pathway can be separated into two phases: The Preparatory/Investment Phase – wherein ATP is consumed. The Pay Off Phase – wherein ATP is produced; the overall reaction of glycolysis is: The use of symbols in this equation makes it appear unbalanced with respect to oxygen atoms, hydrogen atoms, charges. Atom balance is maintained by the two phosphate groups: Each exists in the form of a hydrogen phosphate anion, dissociating to contribute 2 H+ overall Each liberates an oxygen atom when it binds to an ADP molecule, contributing 2 O overallCharges are balanced by the difference between ADP and ATP. In the cellular environment, all three hydroxyl groups of ADP dissociate into −O− and H+, giving ADP3−, this ion tends to exist in an ionic bond with Mg2+, giving ADPMg−.
ATP behaves identically except that it has four hydroxyl groups, giving ATPMg2−. When these differences along with the true charges on the two phosphate groups are considered together, the net charges of −4 on each side are balanced. For simple fermentations, the metabolism of one molecule of glucose to two molecules of pyruvate has a net yield of two molecules of ATP. Most cells will carry out further reactions to'repay' the used NAD+ and produce a final product of ethanol or lactic acid. Many bacteria use inorganic compounds as hydrogen acceptors to regenerate the NAD+. Cells performing aerobic respiration synthesize much more ATP, but not as part of glycolysis; these further aerobic reactions use pyruvate and NADH + H+ from glycolysis. Eukaryotic aerobic respiration produces 34 additional molecules of ATP for each glucose molecule, however most of these are produced by a vastly different mechanism to the substrate-level phosphorylation in glycolysis; the lower-energy production, per glucose, of anaerobic respiration relative to aerobic respiration, results in greater flux through the pathway under hypoxic conditions, unless alternative sources of anaerobically oxidizable substrates, such as fatty acids, are found.
The pathway of glycolysis as it is known today took 100 years to discover. The combined results of many smaller experiments were required in order to understand the pathway as a whole; the first steps in understanding glycolysis began in the nineteenth century with the wine industry. For economic reasons, the French wine industry sought to investigate why wine sometime turned distasteful, instead of fermenting into alcohol. French scientist Louis Pasteur researched this issue during the 1850s, the results of his experiments began the long road to elucidating the pathway of glycolysis, his experiments showed. While Pasteur's experiments were groundbreaking, insight into the component steps of glycolysis were provided by the non-cellular fermentation experiments of Eduard Buchner during the 1890s. Buchner demonstrated that the conversion of glucose to ethanol was possible using a non-living extract of yeast; this experiment not only revolutionized biochemistry, but allowed scientists to analyze this pathway in a more controlled lab setting.
In a series of experiments, scientists Arthur Harden and William Young discovered more pieces of glycolysis. They discovered the regulatory effects of ATP on glucose consumption during alcohol fermentation, they shed light on the role of one compound as a glycolysis intermediate: fructose 1,6-bisphosphate. The elucidation of fructose 1,6-bisphosphate was accomplished by measuring CO2 levels when yeast juice was incubated with glucose. CO2 production increased then slowed down. Harden and Young noted that this process would restart if an inorganic phosphate was added to the mixture. Harden and Young deduced that this process produced organic phosphate esters, further experiments allowed them to extract fructose diphosphate. Arthur Harden and William Young along with Nick Sheppard determined, in a second experiment, that a heat-sensitive high-molecular-weight subcellular fraction and a heat-insensitive low-molecular-weight cytoplasm fraction are required together for fermenta
Glucokinase is an enzyme that facilitates phosphorylation of glucose to glucose-6-phosphate. Glucokinase occurs in cells in the pancreas of humans and most other vertebrates. In each of these organs it plays an important role in the regulation of carbohydrate metabolism by acting as a glucose sensor, triggering shifts in metabolism or cell function in response to rising or falling levels of glucose, such as occur after a meal or when fasting. Mutations of the gene for this enzyme can cause unusual forms of hypoglycemia. Glucokinase is a hexokinase isozyme, related homologously to at least three other hexokinases. All of the hexokinases can mediate phosphorylation of glucose to glucose-6-phosphate, the first step of both glycogen synthesis and glycolysis. However, glucokinase is coded by a separate gene and its distinctive kinetic properties allow it to serve a different set of functions. Glucokinase has a lower affinity for glucose than the other hexokinases do, its activity is localized to a few cell types, leaving the other three hexokinases as more important preparers of glucose for glycolysis and glycogen synthesis for most tissues and organs.
Because of this reduced affinity, the activity of glucokinase, under usual physiological conditions, varies according to the concentration of glucose. Alternative names for this enzyme are: human hexokinase IV, hexokinase D, ATP:D-hexose 6-phosphotransferase, EC 184.108.40.206. The common name, glucokinase, is derived from its relative specificity for glucose under physiologic conditions; some biochemists have argued that the name glucokinase should be abandoned as misleading, as this enzyme can phosphorylate other hexoses in the right conditions, there are distantly related enzymes in bacteria with more absolute specificity for glucose that better deserve the name and the EC 220.127.116.11. Glucokinase remains the name preferred in the contexts of medicine and mammalian physiology. Another mammalian glucose kinase, ADP-specific glucokinase, was discovered in 2004; the gene is similar to that of primitive organisms. It is dependent on ADP rather than ATP, the metabolic role and importance remain to be elucidated.
The principal substrate of physiologic importance of glucokinase is glucose, the most important product is glucose-6-phosphate. The other necessary substrate, from which the phosphate is derived, is adenosine triphosphate, converted to adenosine diphosphate when the phosphate is removed; the reaction catalyzed by glucokinase is: ATP participates in the reaction in a form complexed to magnesium as a cofactor. Furthermore, under certain conditions, like other hexokinases, can induce phosphorylation of other hexoses and similar molecules. Therefore, the general glucokinase reaction is more described as: Hexose + MgATP2− → hexose-PO2−3 + MgADP− + H+Among the hexose substrates are mannose and glucosamine, but the affinity of glucokinase for these requires concentrations not found in cells for significant activity. Two important kinetic properties distinguish glucokinase from the other hexokinases, allowing it to function in a special role as glucose sensor. Glucokinase has a lower affinity for glucose than the other hexokinases.
Glucokinase changes conformation and/or function in parallel with rising glucose concentrations in the physiologically important range of 4–10 mmol/L. It is half-saturated at a glucose concentration of about 8 mmol/L. Glucokinase is not inhibited by its product, glucose-6-phosphate; this allows continued signal output amid significant amounts of its productThese two features allow it to regulate a "supply-driven" metabolic pathway. That is, the rate of reaction is driven by the supply of glucose, not by the demand for end products. Another distinctive property of glucokinase is its moderate cooperativity with glucose, with a Hill coefficient of about 1.7. Glucokinase has only a single binding site for glucose and is the only monomeric regulatory enzyme known to display substrate cooperativity; the nature of the cooperativity has been postulated to involve a "slow transition" between two different enzyme states with different rates of activity. If the dominant state depends upon glucose concentration, it would produce an apparent cooperativity similar to that observed.
Because of this cooperativity, the kinetic interaction of glucokinase with glucose does not follow classical Michaelis-Menten kinetics. Rather than a Km for glucose, it is more accurate to describe a half-saturation level S0.5, the concentration at which the enzyme is 50% saturated and active. The S0.5 and nH extrapolate to an "inflection point" of the curve describing enzyme activity as a function of glucose concentration at about 4 mmol/L. In other words, at a glucose concentration of about 72 mg/dl, near the low end of the normal range, glucokinase activity is most sensitive to small changes in glucose concentration; the kinetic relationship with the other substrate, MgATP, can be described by classical Michaelis-Menten kinetics, with an affinity at about 0.3–0.4 mmol/L, well below a typical intracellular concentration of 2.5 mmol/L. The fact that there is nearly always an excess of ATP available implies that ATP concentration influences glucokinase activity; the maximum specific activity of glucokinase when saturated with both substrates is 62/s.
A "minimal mathematical model" has been devised based on the above kinetic information to predict the beta cell glucose phosphorylation rate of normal glucokinase and the known mutati
An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors, they are used in pesticides. Not all molecules; the binding of an inhibitor can stop a substrate from entering the enzyme's active site and/or hinder the enzyme from catalyzing its reaction. Inhibitor binding is either irreversible. Irreversible inhibitors react with the enzyme and change it chemically; these inhibitors modify key amino acid residues needed for enzymatic activity. In contrast, reversible inhibitors bind non-covalently and different types of inhibition are produced depending on whether these inhibitors bind to the enzyme, the enzyme-substrate complex, or both. Many drug molecules are enzyme inhibitors, so their discovery and improvement is an active area of research in biochemistry and pharmacology. A medicinal enzyme inhibitor is judged by its specificity and its potency. A high specificity and potency ensure.
Enzyme inhibitors occur and are involved in the regulation of metabolism. For example, enzymes in a metabolic pathway can be inhibited by downstream products; this type of negative feedback slows the production line when products begin to build up and is an important way to maintain homeostasis in a cell. Other cellular enzyme inhibitors are proteins that bind to and inhibit an enzyme target; this can help control enzymes that may be damaging like proteases or nucleases. A well-characterised example of this is the ribonuclease inhibitor, which binds to ribonucleases in one of the tightest known protein–protein interactions. Natural enzyme inhibitors can be poisons and are used as defences against predators or as ways of killing prey. Reversible inhibitors attach to enzymes with non-covalent interactions such as hydrogen bonds, hydrophobic interactions and ionic bonds. Multiple weak bonds between the inhibitor and the active site combine to produce strong and specific binding. In contrast to substrates and irreversible inhibitors, reversible inhibitors do not undergo chemical reactions when bound to the enzyme and can be removed by dilution or dialysis.
There are four kinds of reversible enzyme inhibitors. They are classified according to the effect of varying the concentration of the enzyme's substrate on the inhibitor. In competitive inhibition, the substrate and inhibitor cannot bind to the enzyme at the same time, as shown in the figure on the right; this results from the inhibitor having an affinity for the active site of an enzyme where the substrate binds. This type of inhibition can be overcome by sufficiently high concentrations of substrate, i.e. by out-competing the inhibitor. However, the apparent Km will increase as it takes a higher concentration of the substrate to reach the Km point, or half the Vmax. Competitive inhibitors are similar in structure to the real substrate. In uncompetitive inhibition, the inhibitor binds only to the substrate-enzyme complex; this type of inhibition causes Vmax to Km to decrease. In non-competitive inhibition, the binding of the inhibitor to the enzyme reduces its activity but does not affect the binding of substrate.
As a result, the extent of inhibition depends only on the concentration of the inhibitor. Vmax will decrease due to the inability for the reaction to proceed as efficiently, but Km will remain the same as the actual binding of the substrate, by definition, will still function properly. In mixed inhibition, the inhibitor can bind to the enzyme at the same time as the enzyme's substrate. However, the binding of the inhibitor affects the binding of the substrate, vice versa; this type of inhibition can be reduced, but not overcome by increasing concentrations of substrate. Although it is possible for mixed-type inhibitors to bind in the active site, this type of inhibition results from an allosteric effect where the inhibitor binds to a different site on an enzyme. Inhibitor binding to this allosteric site changes the conformation of the enzyme so that the affinity of the substrate for the active site is reduced. Reversible inhibition can be described quantitatively in terms of the inhibitor's binding to the enzyme and to the enzyme-substrate complex, its effects on the kinetic constants of the enzyme.
In the classic Michaelis-Menten scheme below, an enzyme binds to its substrate to form the enzyme–substrate complex ES. Upon catalysis, this complex breaks down to release free enzyme; the inhibitor can bind to ES with the dissociation constants Ki or Ki', respectively. When an enzyme has multiple substrates, inhibitors can show different types of inhibition depending on which substrate is considered; this results from the active site containing two different binding sites within the active site, one for each substrate. For example, an inhibitor might compete with
A carbohydrate is a biomolecule consisting of carbon and oxygen atoms with a hydrogen–oxygen atom ratio of 2:1 and thus with the empirical formula Cmn. This formula holds true for monosaccharides; some exceptions exist. The carbohydrates are technically hydrates of carbon; the term is most common in biochemistry, where it is a synonym of saccharide, a group that includes sugars and cellulose. The saccharides are divided into four chemical groups: monosaccharides, disaccharides and polysaccharides. Monosaccharides and disaccharides, the smallest carbohydrates, are referred to as sugars; the word saccharide comes from the Greek word σάκχαρον, meaning "sugar". While the scientific nomenclature of carbohydrates is complex, the names of the monosaccharides and disaccharides often end in the suffix -ose, as in the monosaccharides fructose and glucose and the disaccharides sucrose and lactose. Carbohydrates perform numerous roles in living organisms. Polysaccharides serve as structural components; the 5-carbon monosaccharide ribose is an important component of coenzymes and the backbone of the genetic molecule known as RNA.
The related deoxyribose is a component of DNA. Saccharides and their derivatives include many other important biomolecules that play key roles in the immune system, preventing pathogenesis, blood clotting, development, they are found in a wide variety of processed foods. Starch is a polysaccharide, it is abundant in cereals and processed food based on cereal flour, such as bread, pizza or pasta. Sugars appear in human diet as table sugar, lactose and fructose, both of which occur in honey, many fruits, some vegetables. Table sugar, milk, or honey are added to drinks and many prepared foods such as jam and cakes. Cellulose, a polysaccharide found in the cell walls of all plants, is one of the main components of insoluble dietary fiber. Although it is not digestible, insoluble dietary fiber helps to maintain a healthy digestive system by easing defecation. Other polysaccharides contained in dietary fiber include resistant starch and inulin, which feed some bacteria in the microbiota of the large intestine, are metabolized by these bacteria to yield short-chain fatty acids.
In scientific literature, the term "carbohydrate" has many synonyms, like "sugar", "saccharide", "ose", "glucide", "hydrate of carbon" or "polyhydroxy compounds with aldehyde or ketone". Some of these terms, specially "carbohydrate" and "sugar", are used with other meanings. In food science and in many informal contexts, the term "carbohydrate" means any food, rich in the complex carbohydrate starch or simple carbohydrates, such as sugar. In lists of nutritional information, such as the USDA National Nutrient Database, the term "carbohydrate" is used for everything other than water, fat and ethanol; this includes chemical compounds such as acetic or lactic acid, which are not considered carbohydrates. It includes dietary fiber, a carbohydrate but which does not contribute much in the way of food energy though it is included in the calculation of total food energy just as though it were a sugar. In the strict sense, "sugar" is applied for sweet, soluble carbohydrates, many of which are used in food.
The name "carbohydrate" was used in chemistry for any compound with the formula Cm n. Following this definition, some chemists considered formaldehyde to be the simplest carbohydrate, while others claimed that title for glycolaldehyde. Today, the term is understood in the biochemistry sense, which excludes compounds with only one or two carbons and includes many biological carbohydrates which deviate from this formula. For example, while the above representative formulas would seem to capture the known carbohydrates and abundant carbohydrates deviate from this. For example, carbohydrates display chemical groups such as: N-acetyl, carboxylic acid and deoxy modifications. Natural saccharides are built of simple carbohydrates called monosaccharides with general formula n where n is three or more. A typical monosaccharide has the structure H–x–y–H, that is, an aldehyde or ketone with many hydroxyl groups added one on each carbon atom, not part of the aldehyde or ketone functional group. Examples of monosaccharides are glucose and glyceraldehydes.
However, some biological substances called "monosaccharides" do not conform to this formula and there are many chemicals that do conform to this formula but are not considered to be monosaccharides. The open-chain form of a monosaccharide coexists with a closed ring form where the aldehyde/ketone carbonyl group carbon and hydroxyl group react forming a hemiacetal with a new C–O–C bridge. Monosaccharides can be linked togeth
Ficus carica is an Asian species of flowering plant in the mulberry family, known as the common fig. It is the source of the fruit called the fig and as such is an important crop in those areas where it is grown commercially. Native to the Middle East and western Asia, it has been sought out and cultivated since ancient times and is now grown throughout the world, both for its fruit and as an ornamental plant; the species has become naturalized in scattered locations in North America. The term fig, first recorded in English in the 13th century, is borrowed from French figue, itself from Occitan figa, from Romance *fica for Classical Latin ficus "fig, fig-tree". Italian has fico, directly inherited from Latin ficus; the name of the caprifig is derived both from Latin capro referring to billygoat and from English fig. Ficus carica is a gynodioecious, deciduous tree or large shrub, growing to a height of 7–10 metres, with smooth white bark, its fragrant leaves are 12–25 centimetres long and 10–18 centimetres across, lobed with three or five lobes.
The complex inflorescence consists of a hollow fleshy structure called the syconium, lined with numerous unisexual flowers. The flowers themselves are not visible from outside the syconium, as they bloom inside the infructescence. Although referred to as a fruit, the fig is the infructescence or scion of the tree, known as a false fruit or multiple fruit, in which the flowers and seeds are borne, it is a hollow-ended stem containing many flowers. The small orifice visible on the middle of the fruit is a narrow passage, which allows the specialized fig wasp Blastophaga psenes to enter the fruit and pollinate the flower, whereafter the fruit grows seeds. See Ficus: Fig fruit and reproduction system; the edible fruit consists of the mature syconium containing numerous one-seeded fruits. The fruit is 3 -- 5 centimetres long, with a green skin, sometimes ripening towards brown. Ficus carica has milky sap; the sap of the fig's green parts is an irritant to human skin. The common fig tree has been cultivated since ancient times and grows wild in dry and sunny areas, with deep and fresh soil.
It prefers light free-draining soils, can grow in nutritionally poor soil. Unlike other fig species, Ficus carica does not always require pollination by a wasp or from another tree, but can be pollinated by the fig wasp, Blastophaga psenes to produce seeds. Fig wasps are not present to pollinate in colder countries like the United Kingdom; the plant can tolerate seasonal drought, the Middle Eastern and Mediterranean climate is suitable for the plant. Situated in a favorable habitat, old specimens when mature can reach a considerable size and form a large dense shade tree, its aggressive root system precludes its use in many urban areas of cities, but in nature helps the plant to take root in the most inhospitable areas. The common fig tree is a phreatophyte that lives in areas with standing or running water, it grows well in the valleys of the rivers and ravines saving no water, having strong need of water, extracted from the ground. The deep-rooted plant searches groundwater, in ravines, or cracks in the rocks.
The fig tree, with the water, cools the environment in hot places, creating a fresh and pleasant habitat for many animals that take shelter in its shade in the times of intense heat. The mountain or rock fig is a wild variety, tolerant of cold dry climates, of the semi-arid rocky mountainous regions of Iran in the Kohestan Mountains of Khorasan. There is a practice among the Italian diaspora living in cold-winter climates of burying fig trees to overwinter them and protect the fruit-producing hard wood from cold; this is a common practice introduced by Italian immigrants in the 19th century in cities such as New York, Philadelphia and Toronto, where winters are too cold to leave the tree exposed. A trench is dug appropriate to the size of the tree, part of the root ball is severed, the tree is bent into the hole, it is wrapped in waterproof material to discourage mould and fungus from developing covered with a heavy layer of soil and fallen leaves. Sometimes plywood or corrugated metal is placed on top to secure the tree in place.
In borderline climates like New York City burying the trees is no longer a requirement as winter lows have become milder. They are wrapped in plastic and other insulating material, or not protected at all if planted in a sheltered spot against a sun-reflecting wall. Ficus carica is dispersed by mammals that scatter their seeds in droppings. Fig fruit is an important food source for much of the fauna in some areas, the tree owes its expansion to those that feed on its fruit; the common fig tree sprouts from the root and stolon tissues. The infructescence is pollinated by a symbiosis with a kind of fig wasp; the fertilized female wasp enters the fig through the scion. She pollinates some of the female flowers, she dies. After weeks of development in their galls, the male wasps emerge before females through holes they produce by chewing the galls; the male wasps fertilize the females by depositing semen in the hole in the gall. The males return to the females and enlarge the holes to enable the females to emerge.
Some males enlarge holes in the scion, which enables female
Simplified molecular-input line-entry system
The simplified molecular-input line-entry system is a specification in the form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules; the original SMILES specification was initiated in the 1980s. It has since been extended. In 2007, an open standard called. Other linear notations include the Wiswesser line notation, ROSDAL, SYBYL Line Notation; the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. Acknowledged for their parts in the early development were "Gilman Veith and Rose Russo and Albert Leo and Corwin Hansch for supporting the work, Arthur Weininger and Jeremy Scofield for assistance in programming the system." The Environmental Protection Agency funded the initial project to develop SMILES. It has since been modified and extended by others, most notably by Daylight Chemical Information Systems.
In 2007, an open standard called "OpenSMILES" was developed by the Blue Obelisk open-source chemistry community. Other'linear' notations include the Wiswesser Line Notation, ROSDAL and SLN. In July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is considered to have the advantage of being more human-readable than InChI; the term SMILES refers to a line notation for encoding molecular structures and specific instances should be called SMILES strings. However, the term SMILES is commonly used to refer to both a single SMILES string and a number of SMILES strings; the terms "canonical" and "isomeric" can lead to some confusion when applied to SMILES. The terms are not mutually exclusive. A number of valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol. Algorithms have been developed to generate the same SMILES string for a given molecule; this SMILES is unique for each structure, although dependent on the canonicalization algorithm used to generate it, is termed the canonical SMILES.
These algorithms first convert the SMILES to an internal representation of the molecular structure. Various algorithms for generating canonical SMILES have been developed and include those by Daylight Chemical Information Systems, OpenEye Scientific Software, MEDIT, Chemical Computing Group, MolSoft LLC, the Chemistry Development Kit. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database; the original paper that described the CANGEN algorithm claimed to generate unique SMILES strings for graphs representing molecules, but the algorithm fails for a number of simple cases and cannot be considered a correct method for representing a graph canonically. There is no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, double bond geometry; these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES.
A notable feature of these rules is. The term isomeric SMILES is applied to SMILES in which isotopes are specified. In terms of a graph-based computational procedure, SMILES is a string obtained by printing the symbol nodes encountered in a depth-first tree traversal of a chemical graph; the chemical graph is first trimmed to remove hydrogen atoms and cycles are broken to turn it into a spanning tree. Where cycles have been broken, numeric suffix labels are included to indicate the connected nodes. Parentheses are used to indicate points of branching on the tree; the resultant SMILES form depends on the choices: of the bonds chosen to break cycles, of the starting atom used for the depth-first traversal, of the order in which branches are listed when encountered. Atoms are represented by the standard abbreviation of the chemical elements, in square brackets, such as for gold. Brackets may be omitted in the common case of atoms which: are in the "organic subset" of B, C, N, O, P, S, F, Cl, Br, or I, have no formal charge, have the number of hydrogens attached implied by the SMILES valence model, are the normal isotopes, are not chiral centers.
All other elements must be enclosed in brackets, have charges and hydrogens shown explicitly. For instance, the SMILES for water may be written as either O or. Hydrogen may be written as a separate atom; when brackets are used, the symbol H is added if the atom in brackets is bonded to one or more hydrogen, followed by the number of hydrogen atoms if greater than 1 by the sign + for a positive charge or by - for a negative charge. For example, for ammonium. If there is more than one charge, it is written as digit.
The avocado is a tree, long thought to have originated in South Central Mexico, classified as a member of the flowering plant family Lauraceae. The fruit of the plant called an avocado, is botanically a large berry containing a single large seed. Avocados are commercially valuable and are cultivated in tropical and Mediterranean climates throughout the world, they have a fleshy body that may be pear-shaped, egg-shaped, or spherical. Commercially, they ripen after harvesting. Avocado trees are self-pollinating and are propagated through grafting to maintain a predictable quality and quantity of the fruit. Persea americana is a tree. Panicles of flowers with deciduous bracts arise from the axils of leaves; the flowers are inconspicuous, 5 -- 10 mm wide. The species is variable because of selection pressure by humans to produce larger, fleshier fruits with a thinner exocarp; the avocado fruit is a climacteric, single-seeded berry, due to the imperceptible endocarp covering the seed, rather than a drupe.
The pear-shaped fruit is 7–20 cm long, weighs between 100 and 1,000 g, has a large central seed, 5–6.4 cm long. Persea americana, or the avocado originated in the Tehuacan Valley in the state of Puebla, although fossil evidence suggests similar species were much more widespread millions of years ago. However, there is evidence for three possible separate domestications of the avocado, resulting in the recognized Mexican and West Indian landraces; the Mexican and Guatemalan landraces originated in the highlands of those countries, while the West Indian landrace is a lowland variety that ranges from Guatemala, Costa Rica, Ecuador to Peru, achieving a wide range through human agency before the arrival of the Europeans. The three separate landraces were most to have intermingled in pre-Columbian America and were described in the Florentine Codex; the earliest residents were living in temporary camps in an ancient wetland eating avocados, mollusks, sharks and sea lions. The oldest discovery of an avocado pit comes from Coxcatlan Cave, dating from around 9,000 to 10,000 years ago.
Other caves in the Tehuacan Valley from around the same time period show early evidence for the presence of avocado. There is evidence for avocado use at Norte Chico civilization sites in Peru by at least 3,200 years ago and at Caballo Muerto in Peru from around 3,800 to 4,500 years ago; the native, undomesticated variety is known as a criollo, is small, with dark black skin, contains a large seed. It coevolved with extinct megafauna; the avocado tree has a long history of cultivation in Central and South America beginning as early as 5,000 BC. A water jar shaped like an avocado, dating to AD 900, was discovered in the pre-Incan city of Chan Chan; the earliest known written account of the avocado in Europe is that of Martín Fernández de Enciso in 1519 in his book, Suma De Geographia Que Trata De Todas Las Partidas Y Provincias Del Mundo. The first detailed account that unequivocally describes the avocado was given by Gonzalo Fernández de Oviedo y Valdés in his work Sumario de la natural historia de las Indias in 1526.
The first written record in English of the use of the word'avocado' was by Hans Sloane, who coined the term in 1669, in a 1696 index of Jamaican plants. The plant was introduced to Spain in 1601, Indonesia around 1750, Mauritius in 1780, Brazil in 1809, the United States mainland in 1825, South Africa and Australia in the late 19th century, Israel in 1908. In the United States, the avocado was introduced to Florida and Hawaii in 1833 and in California in 1856. Before 1915, the avocado was referred to in California as ahuacate and in Florida as alligator pear. In 1915, the California Avocado Association introduced the then-innovative term avocado to refer to the plant; the word "avocado" comes from the Spanish aguacate, which in turn comes from the Nahuatl word āhuacatl, which goes back to the proto-Aztecan *pa:wa which meant "avocado". Sometimes the Nahuatl word was used with the meaning "testicle" because of the likeness between the fruit and the body part; the modern English name comes from an English rendering of the Spanish aguacate as avogato.
The earliest known written use in English is attested from 1697 as "avogato pear", a term, corrupted as "alligator pear". Because the word avogato sounded like "advocate", several languages reinterpreted it to have that meaning. French uses avocat, which means lawyer, "advocate" — forms of the word appear in several Germanic languages, such as the German Advogato-Birne, the old Danish advokat-pære and the Dutch advocaatpeer. In other Central American and Caribbean Spanish-speaking countries, it is known by the Mexican name, while South American Spanish-speaking countries use a Quechua-derived word, palta. In Portuguese, it is abacate; the fruit is sometimes called an avocado alligator pear. The Nahuatl āhuacatl can be compounded with other words, as in ahuacamolli, meaning avocado soup or sauce, from which the Spanish word guacamole derives. In the United Kingdom, the term avocado pear is still sometimes misused as applied when avocados first became available in the 1960s. Originating as a diminutive in Australian English, a clipped form, has since become a common colloquialism in South Africa and the United Kingdom.
It is known as "butter