1.
Neurotoxin
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Neurotoxins are toxins that are poisonous or destructive to nerve tissue. Neurotoxins are a class of exogenous chemical neurological insults that can adversely affect function in both developing and mature nervous tissue. The term can also be used to classify endogenous compounds, which, though neurotoxins are often neurologically destructive, their ability to specifically target neural components is important in the study of nervous systems. Common examples of neurotoxins include lead, ethanol, manganese glutamate, nitric oxide, botulinum toxin, tetanus toxin, some substances such as nitric oxide and glutamate are in fact essential for proper function of the body and only exert neurotoxic effects at excessive concentrations. Neurotoxins inhibit neuron control over ion concentrations across the cell membrane, local pathology of neurotoxin exposure often includes neuron excitotoxicity or apoptosis but can also include glial cell damage. Macroscopic manifestations of neurotoxin exposure can include widespread central nervous system such as intellectual disability, persistent memory impairments, epilepsy. Additionally, neurotoxin-mediated peripheral nervous system such as neuropathy or myopathy is common. Support has been shown for a number of treatments aimed at attenuating neurotoxin-mediated injury, such as antioxidant, exposure to neurotoxins in society is not new, as civilizations have been exposed to neurologically destructive compounds for thousands of years. In part, neurotoxins have been part of history because of the fragile and susceptible nature of the nervous system. The nervous tissue found in the brain, spinal cord, as with any highly complex system, however, even small perturbations to its environment can lead to significant functional disruptions. As a result, the system has a number of mechanisms designed to protect it from internal and external assaults. The blood-brain barrier is one example of protection which prevents toxins. As the brain requires nutrient entry and waste removal, it is perfused by blood flow, blood can carry a number of ingested toxins, however, which would induce significant neuron death if they reach nervous tissue. This barrier creates a hydrophobic layer around the capillaries in the brain. In addition to the BBB, the choroid plexus provides a layer of protection against toxin absorption in the brain, by being hydrophobic and small, or inhibiting astrocyte function, some compounds including certain neurotoxins are able to penetrate into the brain and induce significant damage. Additionally, in vitro systems have increased in use as they provide significant improvements over the common in vivo systems of the past. Examples of improvements include tractable, uniform environments, and the elimination of contaminating effects of systemic metabolism, due to the significant inaccuracies associated with this process, however, it has been slow in gaining widespread support. Though methods of determining neurotoxicity still require significant development, the identification of deleterious compounds, neurotoxins, however, by their very design can be very useful in the field of neuroscience
2.
Asa Gray
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Asa Gray is considered the most important American botanist of the 19th century. His Darwiniana was considered an important explanation of how religion and science were not necessarily mutually exclusive, Gray made several trips to Europe to collaborate with leading European scientists of the era, as well as trips to the southern and western United States. He also built a network of specimen collectors. A prolific writer, he was instrumental in unifying the taxonomic knowledge of the plants of North America, Gray was the sole author of the first five editions of the book and co-author of the sixth, with botanical illustrations by Isaac Sprague. Further editions have been published, and it remains a standard in the field, Gray was born in Sauquoit, New York, on November 18,1810, to Moses Gray, then a tanner, and Roxanna Howard Gray. Born in the back of his fathers tannery, Gray was the eldest of their eight children and his parents married on July 30,1809. Gray was an avid reader even in his youth and he completed Clinton Grammar School from about 1823 to 1825, in those years reading many books from the nearby library at Hamilton College. In 1825 he enrolled at Fairfield Academy, switching to its Fairfield Medical College, also known as the Medical College of the Western District of Fairfield and it was during this time that Gray began to mount botanical specimens. On a trip to New York City, he attempted to meet with John Torrey to get assistance in identifying specimens, Torrey was so impressed with Grays specimens that he began a correspondence with him. Gray graduated and became an M. D. in February 1831, even though he was not yet 21 years of age and it was around this time that he began making explorations in New York and New Jersey. By autumn 1831 he had given up his medical practice to devote more time to botany. In 1832 he was hired to teach chemistry, mineralogy, and botany at Bartletts High School in Utica, New York, Gray first met Torrey in person in September 1832, and they went on an expedition to New Jersey. After completing his assignment in Utica on August 1,1833. By this time, Gray was corresponding and trading specimens with botanists not just in America, but also in Asia, Europe, Gray held a temporary teaching position in 1834 at Hamilton College. He had an apartment in their new building in Manhattan, Torreys attempt to get Gray a job at Princeton University was unsuccessful, as were other attempts to find him a position in science. Despite Gray no longer being his assistant, Torrey and Gray became lifelong friends, Torreys wife, Eliza Torrey, had a profound impact upon Gray in his manners, tastes, habits, and religious life. In October 1836 Gray was selected to be one of the botanists on the United States Exploring Expedition, also known as the Wilkes Expedition, which was supposed to last three years. Gray began getting paid well for his work preparing and planning for this expedition, however, the expedition was fraught with politics, bickering, turmoil, inefficiency, and delays
3.
Rhododendron
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It is the national flower of Nepal. Most species have flowers which bloom from late winter through to early summer. Azaleas make up two subgenera of Rhododendron and they are distinguished from true rhododendrons by having only five anthers per flower. Rhododendron is a genus characterised by shrubs and small to large trees, the smallest species growing to 10–100 cm tall, the leaves are spirally arranged, leaf size can range from 1–2 cm to over 50 cm, exceptionally 100 cm in R. sinogrande. They may be evergreen or deciduous. In some species, the undersides of the leaves are covered with scales or hairs, Some of the best known species are noted for their many clusters of large flowers. There are alpine species with flowers and small leaves. Species in this genus may be part of the complex in oak-heath forests in eastern North America. They have frequently been divided based on the presence or absence of scales on the leaf surface. These scales, unique to subgenus Rhododendron, are modified hairs consisting of a scale attached by a stalk. The Rhododendron genus is the largest of the genera in the Ericaceae family, with 1,024 species, though estimates vary from 850-1000 depending on the authority used, consequently, the taxonomy has been historically complex. He listed five species under Rhododendron, at that time he considered the then known six species of Azalea that he had described earlier in 1735 in his Systema Naturae as a separate genus. Linnaeus six species of Azalea were Azalea indica, A. pontica, A. lutea, A. viscosa, A. lapponica and A. procumbens, which he distinguished from Rhododendron by having five stamens, as opposed to ten. As new species of what are now considered Rhododendron were discovered, for instance Rhodora for Rhododendron canadense, Vireya and Hymenanthes for Rhododendron metternichii, now R. degronianum. Of these Tsutsutsi, Pentanthera, Pogonanthum, Ponticum and Rhodora are still used, the sections being Lepipherum, Booram. Soon, as species became available in the nineteenth century so did a better understanding of the characteristics necessary for the major divisions. Chief amongst these were Maximoviczs Rhododendreae Asiae Orientali and Planchon, maximovicz used flower bud position and its relationship with leaf buds to create eight Sections. Bentham and Hooker used a scheme, but called the divisions Series
4.
Honey
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Honey /ˈhʌni/ is a sugary food substance produced and stored by certain social hymenopteran insects. It is produced from the secretions of plants or insects, such as floral nectar or aphid honeydew, through regurgitation, enzymatic activity. The variety of honey produced by bees is the most well-known, due to its worldwide commercial production. Honey gets its sweetness from the monosaccharides fructose and glucose, and has about the relative sweetness as granulated sugar. It has attractive properties for baking and a distinctive flavor that leads some people to prefer it to sugar. Most microorganisms do not grow in honey, so sealed honey does not spoil, however, honey sometimes contains dormant endospores of the bacterium Clostridium botulinum, which can be dangerous to babies, as it may result in botulism. People who have an immune system should not eat honey because of the risk of bacterial or fungal infection. Although some evidence indicates honey may be effective in treating diseases and other conditions, such as wounds and burns. Providing 64 calories in a serving of one tablespoon equivalent to 1272 kj per 100 g. Honey is generally safe, but may have various, potential adverse effects or interactions with excessive consumption, existing disease conditions, or drugs. Honey use and production have a long and varied history as an ancient activity, depicted in Valencia, in cold weather or when other food sources are scarce, adult and larval bees use stored honey as food. By contriving for bee swarms to nest in man-made hives, people have been able to semidomesticate the insects, Bee digestive enzymes - invertase, amylase, and diastase - and gastric acid hydrolyze sucrose to a mixture of glucose and fructose. The bees work together as a group with the regurgitation and digestion for as long as 20 minutes until the product reaches storage quality. It is then placed in honeycomb cells left unsealed while still high in content and natural yeasts. The bees then cap the cells with wax to seal them, as removed from the hive by a beekeeper, honey has a long shelf life and will not ferment if properly sealed. Another source of honey is from a number of species, such as the wasps Brachygastra lecheguana and Brachygastra mellifica. These species are known to feed on nectar and produce honey, Honey is collected from wild bee colonies, or from domesticated beehives. The honey is stored in honeycombs, wild bee nests are sometimes located by following a honeyguide bird
5.
Pollen
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Pollen is a fine to coarse powdery substance comprising pollen grains which are male microgametophytes of seed plants, which produce male gametes. If pollen lands on a compatible pistil or female cone, it germinates, individual pollen grains are small enough to require magnification to see detail. The study of pollen is called palynology and is useful in paleoecology, paleontology, archaeology. Pollen in plants is used for transferring haploid male genetic material from the anther of a flower to the stigma of another in cross-pollination. In a case of self-pollination, this takes place from the anther of a flower to the stigma of the same flower. Pollen itself is not the male gamete, each pollen grain contains vegetative cells and a generative cell. In flowering plants the vegetative tube cell produces the pollen tube, pollen is produced in the microsporangia in the male cone of a conifer or other gymnosperm or in the anthers of an angiosperm flower. Pollen grains come in a variety of shapes, sizes. Pollen grains of pines, firs, and spruces are winged, the smallest pollen grain, that of the forget-me-not, is around 6 µm in diameter. Wind-borne pollen grains can be as large as about 90–100 µm, in angiosperms, during flower development the anther is composed of a mass of cells that appear undifferentiated, except for a partially differentiated dermis. As the flower develops, four groups of cells form within the anther. The fertile sporogenous cells are surrounded by layers of cells that grow into the wall of the pollen sac. Some of the cells grow into nutritive cells that supply nutrition for the microspores that form by meiotic division from the sporogenous cells, in a process called microsporogenesis, four haploid microspores are produced from each diploid sporogenous cell, after meiotic division. After the formation of the four microspores, which are contained by callose walls, the exine is what is preserved in the fossil record. Two basic types of microsporogenesis are recognised, simultaneous and successive, in simultaneous microsporogenesis meiotic steps I and II are completed prior to cytokinesis, whereas in successive microsporogenesis cytokinesis follows. While there may be a continuum with intermediate forms, the type of microsporogenesis has systematic significance, the predominant form amongst the monocots is successive, but there are important exceptions. During microgametogenesis, the unicellular microspores undergo mitosis and develop into mature microgametophytes containing the gametes, in some flowering plants, germination of the pollen grain may begin even before it leaves the microsporangium, with the generative cell forming the two sperm cells. Except in the case of submerged aquatic plants, the mature pollen grain has a double wall
6.
Nectar
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Common nectar-consuming pollinators include mosquitoes, hoverflies, wasps, bees, butterflies and moths, hummingbirds, and bats. M. scutellata and the honey bee. Nectar is an important item, the sugar source for honey. It is also useful in agriculture and horticulture because the adult stages of some predatory insects feed on nectar, for example, the social wasp species Apoica flavissima relies on nectar as a primary food source. In turn, these wasps then hunt agricultural pest insects as food for their young, for example, thread-waisted wasps are known for hunting caterpillars that are destructive to crops. Caterpillars however, do eventually become butterflies and moths, which are important pollinators. Nectar secretion increases as the flower is visited by pollinators, after pollination, the nectar is frequently reabsorbed into the plant. Nectar is derived from Greek nektar, the drink of the gods. The current meaning, sweet liquid in flowers, is first recorded in AD1600, floral nectaries are generally located at the base of the perianth, so pollinators are made to brush the flowers reproductive structures, the stamen and pistil, while accessing the nectar. A septal nectary is nectar-producing tissue that is found in the wall of a plant ovary, septal nectaries function as a way of attracting pollinators. Plants that rely on insects, birds, or bats for pollination often have septal nectaries, aside from attracting pollinators, septal nectaries have also been known to attract plant protectors. Some plants, like Ruellia radicans, have nectaries that continue to secrete nectar even after the petals have been shed and this attracts ants which will in turn protect the developing fruits of the plant from seed predators and herbivores in exchange for nectar. Extrafloral nectaries are nectar-secreting plant glands that develop outside of flowers and are not involved in pollination and they are highly diverse in form, location, size, and mechanism. They have been described in virtually all above-ground plant parts—including leaves, petioles, stipules, cotyledons, fruits and they range from single-celled trichomes to complex cup-like structures that may or may not be vascularized. In contrast to floral nectaries, nectar produced outside the flower generally have a defensive function, the nectar attracts predatory insects which will eat both the nectar and any plant-eating insects around, thus functioning as bodyguards. Foraging predatory insects show a preference for plants with extrafloral nectaries, particularly species of ants and wasps. Among passion flowers, for example, extrafloral nectaries prevent herbivores by attracting ants, in many carnivorous plants, extrafloral nectaries are also used to attract insect prey. Extrafloral nectaries were originally believed to simply be excretory in nature and their defensive functions were first recognized by the Italian botanist Federico Delpino in his important monograph Funzione mirmecofila nel regno vegetale
7.
Nepal
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Nepal, officially the Federal Democratic Republic of Nepal, is a landlocked central Himalayan country in South Asia. Nepal is divided into 7 provinces and 75 districts and 744 local units including 4 metropolises,13 sub-metropolises,246 municipal councils and 481 village and it has a population of 26.4 million and is the 93rd largest country by area. Bordering China in the north and India in the south, east, Nepal does not border Bangladesh, which is located within only 27 km of its southeastern tip. It neither borders Bhutan due to the Indian state of Sikkim being located in between, Nepal has a diverse geography, including fertile plains, subalpine forested hills, and eight of the worlds ten tallest mountains, including Mount Everest, the highest point on Earth. Kathmandu is the capital and largest city. It is a nation with Nepali as the official language. The territory of Nepal has a history since the Neolithic age. The name Nepal is first recorded in texts from the Vedic Age, the era which founded Hinduism, in the middle of the first millennium BCE, Gautama Buddha, the founder of Buddhism, was born in southern Nepal. Parts of northern Nepal were intertwined with the culture of Tibet, the Kathmandu Valley in central Nepal became known as Nepal proper because of its complex urban civilization. It was the seat of the prosperous Newar confederacy known as Nepal Mandala, the Himalayan branch of the ancient Silk Road was dominated by the valleys traders. The cosmopolitan region developed distinct traditional art and architecture, by the 18th century, the Gorkha Kingdom achieved the unification of Nepal. The Shah dynasty established the Kingdom of Nepal and later formed an alliance with the British Empire, the country was never colonized but served as a buffer state between Imperial China and Colonial India. In the 20th century, Nepal ended its isolation and forged ties with regional powers. Parliamentary democracy was introduced in 1951, but was suspended by Nepalese monarchs in 1960 and 2005. The Nepalese Civil War resulted in the proclamation of a republic in 2008, modern Nepal is a federal secular parliamentary republic. Nepal is a nation, ranking 144th on the Human Development Index in 2016. The country struggles with the transition from a monarchy to a republic and it also suffers from high levels of hunger and poverty. Despite these challenges, Nepal is making progress, with the government declaring its commitment to elevate the nation from least developed country status by 2022
8.
Turkey
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Turkey, officially the Republic of Turkey, is a transcontinental country in Eurasia, mainly in Anatolia in Western Asia, with a smaller portion on the Balkan peninsula in Southeast Europe. Turkey is a democratic, secular, unitary, parliamentary republic with a cultural heritage. The country is encircled by seas on three sides, the Aegean Sea is to the west, the Black Sea to the north, and the Mediterranean Sea to the south. The Bosphorus, the Sea of Marmara, and the Dardanelles, Ankara is the capital while Istanbul is the countrys largest city and main cultural and commercial centre. Approximately 70-80% of the countrys citizens identify themselves as ethnic Turks, other ethnic groups include legally recognised and unrecognised minorities. Kurds are the largest ethnic minority group, making up approximately 20% of the population, the area of Turkey has been inhabited since the Paleolithic by various ancient Anatolian civilisations, as well as Assyrians, Greeks, Thracians, Phrygians, Urartians and Armenians. After Alexander the Greats conquest, the area was Hellenized, a process continued under the Roman Empire. The Seljuk Sultanate of Rûm ruled Anatolia until the Mongol invasion in 1243, the empire reached the peak of its power in the 16th century, especially during the reign of Suleiman the Magnificent. During the war, the Ottoman government committed genocides against its Armenian, Assyrian, following the war, the conglomeration of territories and peoples that formerly comprised the Ottoman Empire was partitioned into several new states. Turkey is a member of the UN, an early member of NATO. Turkeys growing economy and diplomatic initiatives have led to its recognition as a regional power while her location has given it geopolitical, the name of Turkey is based on the ethnonym Türk. The first recorded use of the term Türk or Türük as an autonym is contained in the Old Turkic inscriptions of the Göktürks of Central Asia, the English name Turkey first appeared in the late 14th century and is derived from Medieval Latin Turchia. Similarly, the medieval Khazar Empire, a Turkic state on the shores of the Black. The medieval Arabs referred to the Mamluk Sultanate as al-Dawla al-Turkiyya, the Ottoman Empire was sometimes referred to as Turkey or the Turkish Empire among its European contemporaries. The Anatolian peninsula, comprising most of modern Turkey, is one of the oldest permanently settled regions in the world, various ancient Anatolian populations have lived in Anatolia, from at least the Neolithic period until the Hellenistic period. Many of these peoples spoke the Anatolian languages, a branch of the larger Indo-European language family, in fact, given the antiquity of the Indo-European Hittite and Luwian languages, some scholars have proposed Anatolia as the hypothetical centre from which the Indo-European languages radiated. The European part of Turkey, called Eastern Thrace, has also been inhabited since at least forty years ago. It is the largest and best-preserved Neolithic site found to date, the settlement of Troy started in the Neolithic Age and continued into the Iron Age
9.
Kalmia
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Kalmia is a genus of about 8 species of evergreen shrubs from 0. 2–5 m tall, in the family Ericaceae. They are native to North America and Cuba and they grow in acidic soils, with different species in wet acid bog habitats and dry, sandy soils. Kalmia was named by Linnaeus to honour his friend the botanist Pehr Kalm, earlier Mark Catesby saw it during his travels in Carolina, and after his return to England in 1726, imported seeds. The leaves are 2–12 cm long and simple lanceolate, the flowers are white, pink or purple, in corymbs of 10-50, reminiscent of Rhododendron flowers but flatter, with a star-like calyx of five conjoined petals, each flower is 1–3 cm diameter. The fruit is a capsule, which splits to release the numerous small seeds. The foliage is toxic if eaten, with sheep being particularly prone to poisoning, other names for Kalmia, particularly Kalmia angustifolia, are sheep-laurel, lamb-kill, calf-kill, kill-kid, and sheep-poison, which may be written with or without the hyphen. Kid here refers to a goat, not a human child. It has also been called spoonwood because Kalm was told by Dutch settlers of North America that Native Americans made spoons from the wood, given its toxicity, this may be folklore rather than scientific fact. Kalmias are popular garden shrubs, grown for their decorative flowers and they should not be planted where they are accessible to livestock due to the toxicity. Kalmia species are used as food plants by the larvae of some species including Coleophora kalmiella which feeds exclusively on Kalmia. Kalmia angustifolia L. - Sheep-laurel, Lambkill Kalmia buxifolia Gift & Kron - Sandmyrtle Kalmia carolina Small - Carolina Mountain-laurel Kalmia cuneata Michx, - Whitewicky Kalmia ericoides Wright - Cuban Kalmia Kalmia hirsuta Walt. - Hairy Mountain-laurel Kalmia latifolia L. - Mountain-laurel, Lambkill Kalmia microphylla A, - Bog Kalmia, Bog-laurel Kalmia procumbens Gift & Kron - Alpine azalea The related Kalmiopsis is a rare shrub native to the Siskiyou Mountains of southwest Oregon. Jaynes, Richard A.1997, Kalmia, mountain laurel and related species, Timber Press, Portland, Oregon, info about Kalmia latifolia European Kalmia Society A German hybridizer
10.
Black Sea
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The Black Sea is a body of water between Eastern Europe and Western Asia, bounded by Bulgaria, Georgia, Romania, Russia, Turkey, and Ukraine. It is supplied by a number of rivers, such as the Danube, Dnieper, Rioni, Southern Bug. The Black Sea has an area of 436,400 km2, a depth of 2,212 m. It is constrained by the Pontic Mountains to the south and by the Caucasus Mountains to the east, the longest east-west extent is about 1,175 km. The Black Sea has a water balance, that is, a net outflow of water 300 km3 per year through the Bosphorus. Mediterranean water flows into the Black Sea as part of a two-way hydrological exchange, the Black Sea drains into the Mediterranean Sea and then the Atlantic Ocean, via the Aegean Sea and various straits. The Bosphorus Strait connects it to the Sea of Marmara, and these waters separate Eastern Europe and Western Asia. The Black Sea is also connected to the Sea of Azov by the Strait of Kerch, the water level has varied significantly. Due to these variations in the level in the basin. At certain critical water levels it is possible for connections with surrounding water bodies to become established and it is through the most active of these connective routes, the Turkish Straits, that the Black Sea joins the world ocean. When this hydrological link is not present, the Black Sea is a basin, operating independently of the global ocean system. Currently the Black Sea water level is high, thus water is being exchanged with the Mediterranean. The Turkish Straits connect the Black Sea with the Aegean Sea, and comprise the Bosphorus, the Sea of Marmara, the International Hydrographic Organization defines the limits of the Black Sea as follows, On the Southwest. The Northeastern limit of the Sea of Marmara, a line joining Cape Takil and Cape Panaghia. Strabos Geographica reports that in antiquity, the Black Sea was often just called the Sea, for the most part, Graeco-Roman tradition refers to the Black Sea as the Hospitable sea, Εὔξεινος Πόντος Eúxeinos Póntos. This is a euphemism replacing an earlier Inhospitable Sea, Πόντος Ἄξεινος Póntos Áxeinos, strabo thinks that the Black Sea was called inhospitable before Greek colonization because it was difficult to navigate, and because its shores were inhabited by savage tribes. The name was changed to hospitable after the Milesians had colonized the southern shoreline and it is also possible that the epithet Áxeinos arose by popular etymology from a Scythian word axšaina- unlit, dark, the designation Black Sea may thus date from antiquity. A map of Asia dating to 1570, entitled Asiae Nova Descriptio, from Abraham Orteliuss Theatrum Orbis Terrarum, english-language writers of the 18th century often used the name Euxine Sea to refer to the Black Sea
11.
Nitrogen
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Nitrogen is a chemical element with symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772, although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about the same time, Rutherford is generally accorded the credit because his work was published first. Nitrogen is the lightest member of group 15 of the periodic table, the name comes from the Greek πνίγειν to choke, directly referencing nitrogens asphyxiating properties. It is an element in the universe, estimated at about seventh in total abundance in the Milky Way. At standard temperature and pressure, two atoms of the element bind to form dinitrogen, a colourless and odorless diatomic gas with the formula N2, dinitrogen forms about 78% of Earths atmosphere, making it the most abundant uncombined element. Nitrogen occurs in all organisms, primarily in amino acids, in the nucleic acids, the human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes movement of the element from the air, into the biosphere and organic compounds, many industrially important compounds, such as ammonia, nitric acid, organic nitrates, and cyanides, contain nitrogen. The extremely strong bond in elemental nitrogen, the second strongest bond in any diatomic molecule. Synthetically produced ammonia and nitrates are key industrial fertilisers, and fertiliser nitrates are key pollutants in the eutrophication of water systems. Apart from its use in fertilisers and energy-stores, nitrogen is a constituent of organic compounds as diverse as Kevlar used in high-strength fabric, Nitrogen is a constituent of every major pharmacological drug class, including antibiotics. Many notable nitrogen-containing drugs, such as the caffeine and morphine or the synthetic amphetamines. Nitrogen compounds have a long history, ammonium chloride having been known to Herodotus. They were well known by the Middle Ages, alchemists knew nitric acid as aqua fortis, as well as other nitrogen compounds such as ammonium salts and nitrate salts. The mixture of nitric and hydrochloric acids was known as aqua regia, celebrated for its ability to dissolve gold, the discovery of nitrogen is attributed to the Scottish physician Daniel Rutherford in 1772, who called it noxious air. Though he did not recognise it as a different chemical substance, he clearly distinguished it from Joseph Blacks fixed air. The fact that there was a component of air that does not support combustion was clear to Rutherford, Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as air or azote, from the Greek word άζωτικός. In an atmosphere of nitrogen, animals died and flames were extinguished
12.
Alpha helix
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This secondary structure is also sometimes called a classic Pauling–Corey–Branson α-helix. The name 3. 613-helix is also used for type of helix, denoting the average number of residues per helical turn. Among types of structure in proteins, the α-helix is the most regular. In the early 1930s, William Astbury showed that there were changes in the X-ray fiber diffraction of moist wool or hair fibers upon significant stretching. The data suggested that the unstretched fibers had a molecular structure with a characteristic repeat of ~5.1 ångströms. Astbury initially proposed a structure for the fibers. He later joined other researchers in proposing that, the protein molecules formed a helix the stretching caused the helix to uncoil. Hans Neurath was the first to show that Astburys models could not be correct in detail, neuraths paper and Astburys data inspired H. S. Taylor, Maurice Huggins and Bragg and collaborators to propose models of keratin that somewhat resemble the modern α-helix. The pivotal moment came in the spring of 1948, when Pauling caught a cold. Being bored, he drew a polypeptide chain of roughly correct dimensions on a strip of paper and folded it into a helix, after a few attempts, he produced a model with physically plausible hydrogen bonds. Pauling then worked with Corey and Branson to confirm his model before publication. The amino acids in an α-helix are arranged in a helical structure where each amino acid residue corresponds to a 100° turn in the helix. Dunitz describes how Paulings first article on the theme in fact shows a left-handed helix, short pieces of left-handed helix sometimes occur with a large content of achiral glycine amino acids, but are unfavorable for the other normal, biological L-amino acids. The pitch of the alpha-helix is 5.4 Å, which is the product of 1.5 and 3.6, the alpha-helices can be identified in protein structure using several computational methods, one of which being DSSP. Similar structures include the 310 helix and the π-helix, the subscripts refer to the number of atoms in the closed loop formed by the hydrogen bond. Residues in α-helices typically adopt backbone dihedral angles around, as shown in the image at right, in more general terms, they adopt dihedral angles such that the ψ dihedral angle of one residue and the φ dihedral angle of the next residue sum to roughly -105°. As a consequence, α-helical dihedral angles, in general, fall on a stripe on the Ramachandran diagram. For comparison, the sum of the angles for a 310 helix is roughly -75°
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