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Selenocysteine

Selenocysteine is the 21st proteinogenic amino acid. Selenocysteine exists in all three domains of life, but not in every lineage, as a building block of selenoproteins. Selenocysteine is a cysteine analogue with a selenium-containing selenol group in place of the sulfur-containing thiol group. Selenocysteine is present in several enzymes. Selenocysteine was discovered by biochemist Thressa Stadtman at the National Institutes of Health. Selenocysteine has a structure similar to that of cysteine, but with an atom of selenium taking the place of the usual sulfur, forming a selenol group, deprotonated at physiological pH. (Like other natural proteinogenic amino acids and selenocysteine have L chirality in the older D/L notation based on homology to D- and L-glyceraldehyde. In the newer R/S system of designating chirality, based on the atomic numbers of atoms near the asymmetric carbon, they have R chirality, because of the presence of sulfur or selenium as a second neighbor to the asymmetric carbon.

Proteins which contain one or more selenocysteine residues are called selenoproteins. Most selenoproteins contain a single selenocysteine residue. Selenoproteins which depend on selenocysteine's catalytic activity are called selenoenzymes. Selenoenzymes have been found to employ catalytic triad structures that influence the nucleophilicity of the active site selenocysteine. Selenocysteine has both a lower reduction potential than cysteine; these properties make it suitable in proteins that are involved in antioxidant activity. Although it is found in the three domains of life, it is not universal in all organisms. Unlike other amino acids present in biological proteins, selenocysteine is not coded for directly in the genetic code. Instead, it is encoded in a special way by a UGA codon, a stop codon; such a mechanism is called translational recoding and its efficiency depends on the selenoprotein being synthesized and on translation initiation factors. When cells are grown in the absence of selenium, translation of selenoproteins terminates at the UGA codon, resulting in a truncated, nonfunctional enzyme.

The UGA codon is made to encode selenocysteine by the presence of a selenocysteine insertion sequence in the mRNA. The SECIS element is defined by characteristic nucleotide sequences and secondary structure base-pairing patterns. In bacteria, the SECIS element is located following the UGA codon within the reading frame for the selenoprotein. In Archaea and in eukaryotes, the SECIS element is in the 3′ untranslated region of the mRNA and can direct multiple UGA codons to encode selenocysteine residues. Again unlike the other amino acids, no free pool of selenocysteine exists in the cell, its high reactivity would cause damage to cells. Instead, cells store selenium in the less reactive oxidized form, selenocystine, or in methylated form, selenomethionine. Selenocysteine synthesis occurs on a specialized tRNA, which functions to incorporate it into nascent polypeptides; the primary and secondary structure of selenocysteine-specific tRNA, tRNASec, differ from those of standard tRNAs in several respects, most notably in having an 8-base-pair or 10-base-pair acceptor stem, a long variable region arm, substitutions at several well-conserved base positions.

The selenocysteine tRNAs are charged with serine by seryl-tRNA ligase, but the resulting Ser-tRNASec is not used for translation because it is not recognised by the normal translation elongation factor. Rather, the tRNA-bound seryl residue is converted to a selenocysteine residue by the pyridoxal phosphate-containing enzyme selenocysteine synthase. In eukaryotes and archaea, two enzymes are required to convert tRNA-bound seryl residue into tRNA selenocysteinyl residue: PSTK and selenocysteine synthase; the resulting Sec-tRNASec is bound to an alternative translational elongation factor, which delivers it in a targeted manner to the ribosomes translating mRNAs for selenoproteins. The specificity of this delivery mechanism is brought about by the presence of an extra protein domain or an extra subunit which bind to the corresponding RNA secondary structures formed by the SECIS elements in selenoprotein mRNAs. Selenocysteine is decomposed by the enzyme selenocysteine lyase into selenide; as of 2016, fifty-four human proteins are known to contain selenocysteine.

Selenocysteine derivatives γ-glutamyl-Se-methylselenocysteine and Se-methylselenocysteine occur in plants of the genera Allium and Brassica. Biotechnological applications of selenocysteine include use of 73Se-labeled Sec in positron emission tomography studies and 75Se-labeled Sec in specific radiolabeling, facilitation of phase determination by multiwavelength anomalous diffraction in X-ray crystallography of proteins by introducing Sec alone, or Sec together with selenomethionine, incorporation of the stable 77Se isotope, which has a nuclear spin of 1/2 and can be used for high-resolution NMR, among others. Pyrrolysine, another amino acid not in the basic set of 20. Selenomethionine, another selenium-containing amino acid, randomly substitute

Shane Casey

Shane Casey is an Irish sportsperson. He plays hurling with the Waterford senior inter-county team. Casey has played with this local club, Dunhill since underage and presently plays with the club in the Waterford Intermediate Hurling Championship and the Waterford Intermediate Football Championship. At underage, Casey played with the amalgamation club Dunhill/Fenor. At inter-county level, Casey plays with Waterford. Casey made his championship debut on 26 July 2009 having been named in the team to face Galway in the 2009 All-Ireland quarter-final. Casey presently plays with the Waterford under-21 team. Casey will feature in the team to face Clare in the Munster Under-21 Hurling Final on 29 July 2009. Waterford GAA website Dunhill GAA Club website

7204 Ondřejov

7204 Ondřejov, provisional designation 1995 GH, is a stony asteroid from the middle region of the asteroid belt 6 kilometers in diameter. It was discovered on 3 April 1995, by Czech astronomer Petr Pravec at Ondřejov Observatory near Prague, Czech Republic; this asteroid was the observatory's first numbered minor planet discovery. It was named for the Czech village of its discovering observatory. Ondřejov orbits the Sun in the central main-belt at a distance of 2.3–3.0 AU once every 4 years and 4 months. Its orbit has an inclination of 5 ° with respect to the ecliptic, it was first identified as 1980 WM3 at Palomar Observatory in 1980, extending the body's observation arc by 15 years prior to its official discovery observation at Ondrejov. In December 2011, a rotational lightcurve of Ondřejov was obtained from photometric observations taken at the Palomar Transient Factory in California, it showed a rotation period of 5.2334 hours with a brightness variation of 0.55 magnitude. According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, the asteroid measures 5.9 kilometers in diameter and its surface has an albedo of 0.18, while the Collaborative Asteroid Lightcurve Link assumes a lower albedo of 0.10 and calculates a diameter of 6.3 kilometers with an absolute magnitude of 14.14.

This minor planet was named for both, the Czech village of Ondřejov, its discovering Ondřejov Observatory, founded in 1898. Ondřejov is the Czech Republic's oldest astronomical observatory still in use. In 1953, the observatory was integrated into the Astronomical Institute and is now owned by the Academy of Sciences of the Czech Republic. Ondřejov is located about 35 kilometers southeast of Prague; the approved naming citation was published by the Minor Planet Center on 22 February 1997. Asteroid Lightcurve Database, query form Dictionary of Minor Planet Names, Google books Asteroids and comets rotation curves, CdR – Observatoire de Genève, Raoul Behrend Discovery Circumstances: Numbered Minor Planets - – Minor Planet Center 7204 Ondřejov at AstDyS-2, Asteroids—Dynamic Site Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info 7204 Ondřejov at the JPL Small-Body Database Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters

McClain County, Oklahoma

McClain County is a county located in south central Oklahoma. As of the 2010 census, the population was 34,506, its county seat is Purcell. The county was named for an Oklahoma constitutional convention attendee. McClain County is part of the Oklahoma City, OK Metropolitan Statistical Area; the Chickasaw tribe began moving into this area in 1837, when the land had been assigned to the Choctaws by the U. S. government. In 1855, the area became part of the Chickasaw Nation, after the two tribes separated; the present McClain County became part of Pontotoc County, Chickasaw Nation and remained such until Oklahoma attained statehood. Few Chickasaws lived here because of hostilities with western tribes. Major Richard Mason established Camp Holmes in 1835, near the present city of Lexington, while negotiating a treaty between the western tribes and the newly arrived Choctaws. Federal troops abandoned the camp in August 1835. Auguste Pierre Chouteau built a trading post at the Camp Holmes site, but it closed after Chouteau died in 1838.

Randolph Marcy is credited with bringing the California Road through this area in 1849. The U. S. Army built Camp Arbuckle in 1850 to protect the road, but the troops were withdrawn to what is now Garvin County, Oklahoma in the following year. Jesse Chisholm operated a trading post in this area around 1850. A group of Delaware Indians occupied the former camp known as Beaversville, but left before the outbreak of the Civil War. Montford T. Johnson, a rancher, moved to this area after the Civil War, he and Jesse Chisholm, who acted as the negotiator, obtained an agreement with the Chickasaw leaders to allow ranching on their land, provided no whites were employed. Thereafter, Johnson hired a Chickasaw freedman to operate it, he established other ranches and hired another freedman to run those. The Southern Kansas Railway built a line south from Kansas to present McClain County in 1886-7, the Gulf and Santa Fe Railway built a line north from Texas, meeting at and founding the town of Purcell. Eastern Oklahoma Railroad laid tracks in 1900-04 from Newkirk to Pauls Valley, passing through eastern McClain County.

In 1906 the Oklahoma Central Railway built a line that traversed McClain County from the southeast to the northwest. It ran through Byars and Purcell, established Washington and Blanchard. Purcell was a starting point for the Land Run of 1889, it was at the dividing line between Indian Territory, where alcohol could not be sold, Oklahoma Territory, where alcohol sale was legal. The town of Lexington, across the river from Purcell, had numerous saloons. In 1899, the Purcell Bridge Company built a toll bridge across the river, profiting from the alcohol trade. According to the U. S. Census Bureau, the county has a total area of 580 square miles, of which 571 square miles is land and 9.6 square miles is water. The county lies in the Red Bed Plains region of the Osage Plains; the western part of the county is hilly and covered with black jack oak trees, while the eastern part is level lowlands. The South Canadian River forms the northern border, The Washita River flows through the southwestern corner, is fed by several McClain County creeks.

Cleveland County Pottawatomie County Pontotoc County Garvin County Grady County As of the 2010 United States Census, there were 34,506 people, 12,891 households, 9,785 families residing in the county. The population density was 59.5 people per square mile. There were 13,996 housing units at an average density of 24 per square mile; the racial makeup of the county was 84.5% white, 0.7% black or African American, 6.4% Native American, 0.4% Asian, less than 0.1% Pacific Islander, 2.7% from other races, 5.3% from two or more races. Seven percent of the population were Latino of any race. There were 12,891 households, out of which 37.4% included children under the age of 18, 61.3% were married couples living together, 9.9% had a female householder with no husband present, 4.7% had a male householder with no wife present, 24.1% were non-families. Individuals living alone accounted for 20.1% of households and individuals 65 years of age or older living alone accounted for 8.1%. The average household size was 2.66 and the average family size was 3.06.

In the county, the population was spread out with 26.6% under the age of 18, 6.9% from 18 to 24, 25.7% from 25 to 44, 27.6% from 45 to 64, 13.2% who were 65 years of age or older. The median age was 38.2 years. For every 100 females, there were 98.5 males. For every 100 females age 18 and over, there were 95.4 males. The median income for a household in the county was $56,126, the median income for a family was $67,948. Males had a median income of $42,262 versus $32,821 for females; the per capita income for the county was $24,898. About 8% of families and 12% of the population were below the poverty line, including 11% of those under age 18 and 8% of those age 65 or over; the county economy has been based on agriculture and cattle raising. Each town had its own cotton gin early in the 1900s. Purcell had a flour mill. Otherwise, there was little industrial activity. Many county residents commute to work in the Oklahoma City area. Mid-America Area Vo-Tech opened in 1971 to provide vocational education to students.

Duke Energy North America built a power plant near Newcastle in 2001. The Chickasaw Nation operated a gaming casino at Newcastle. Pioneer Library System

Riiser-Larsen Ice Shelf

Riiser-Larsen Ice Shelf is an ice shelf about 250 miles long on the coast of Queen Maud Land, extending from Cape Norvegia in the north to Lyddan Island and Stancomb-Wills Glacier in the south. Parts of the ice shelf were sighted by William Speirs Bruce in 1904, Ernest Shackleton in 1915, Hjalmar Riiser-Larsen in 1930. Most of it was photographed from the air in 1951-52 by the Norwegian-British-Swedish Antarctic Expedition and delineated from these photos. Additional delineation of the southern and landward margins of the feature was accomplished from air photos taken, by USN Operation Deep Freeze from 1967 to 1969; the feature was named by Norway for Capt. Hjalmar Riiser-Larsen, who explored the area in the late 1920s and early 1930s. Cape Vestkapp Emperor penguins mass mourning after chicks die on Antarctic ice shelf This article incorporates public domain material from the United States Geological Survey document "Riiser-Larsen Ice Shelf"

Emil Cohn

Emil Georg Cohn, was a German physicist. Cohn was born in Neustrelitz, Mecklenburg on 28 September 1854, he was the son of August Cohn, a lawyer, Charlotte Cohn. At the age of 17, Cohn began to study jurisprudence at the University of Leipzig. However, at the Ruprecht Karl University of Heidelberg and the University of Strasbourg he began to study physics. In Strasbourg, he graduated in 1879. From 1881 to 1884, he was an assistant of August Kundt at the physical institute. In 1884 he was admitted as a private lecturer. From 1884 to 1918, he was a faculty member of the University of Strasbourg and was nominated as an assistant professor on 27 September 1884, he dealt with experimental physics at first, turned to theoretical physics. In 1918 he was nominated as an extraordinary professor. After the end of World War I and the occupation of Alsace-Lorraine by France and his family were expelled from Strasbourg on the Christmas Eve of 1918. In April 1919, he was nominated as a professor at the University of Rostock.

From June 1920, he gave lectures about theoretical physics at the University of Freiburg. In 1935 he retired in Heidelberg where he lived until 1939, he resigned from the Deutsche Physikalische Gesellschaft together with other physicists like Richard Gans, Leo Graetz, George Jaffé, Walter Kaufmann, in protest at the despotism of the Nazi regime. Cohn was a baptized Protestant and was married with Marie Goldschmidt, with whom he had two daughters; because of his Jewish descent he found himself forced to emigrate to Switzerland because of the pressure under the Nazi regime. He lived in Hasliberg-Hohfluh at first, from 1942 in Ringgenberg, where he died at the age of 90. Cohn's younger brother, Carl Cohn was a successful overseas merchant from Hamburg, who worked from 1921 until 1929 as a senator in Hamburg. At the beginning of the 20th century, Cohn was one of the most respectable experts in the area of theoretical electrodynamics, he was unsatisfied with the Lorentzian theory of electrodynamics for moving bodies and proposed an independent theory.

His alternative theory, based on a modification of the Maxwell field-equations, was compatible to all relevant electrodynamic and optical experiments known at that time, including the Michelson-Morley experiment of 1887. Cohn's electrodynamics of moving bodies was based on the assumption that light travels within the Earth's atmosphere with a constant velocity - however, his theory suffered from internal failures. While the theory predicted the negative result of MMX within air, a positive result would be expected within vacuum. Another weak point stems from the fact, that his concept was formulated without the use of atoms and electrons. So after 1905 his theory was superseded by Albert Einstein's. Regarding his own theory, he used the Principle of Economy to eliminate the known concept of luminiferous aether and argued that one can call it vacuum, he maintained that one can use a frame of reference in which the fixed stars are at rest. As a heuristic concept this can be described as a material "aether", but in Cohn's opinion this would be only "metaphorical" and would not affect the consequences of his theory.

He incorporated the transformation equations x'=x-vt and t'=t-vx/c² introduced by Lorentz in 1895 into his theory, calling them the "Lorentzian Transformation". In 1905 this name was altered by Henri Poincaré into the used expression "Lorentz transformation". In 1904 he compared his theory with Lorentz's mature 1904 theory, employing physical interpretations of the Lorentz transformation that were similar to those used in Albert Einstein's special relativity in 1905. For instance, local time was described by him as a consequence of the assumption that light propagates in spherical waves with constant velocity in all directions. Everywhere, where the propagation of radiation is not the object of measurement, we define identical moments of time at different points of Earth's surface, by treating the propagation of light as timeless. In optics, however, we define these identical moments of time by assuming, that the propagation takes place in spherical waves for every resting and isotropic medium.

This means: the "time" which serves us for the representation of terrestrial processes, is the "local time" t ′, for which the equations I'b to IVb hold, – not the "general time" t. He illustrated the effects of length contraction and time dilation by using moving rods and clocks. X 0 y 0 z 0 are those measuring numbers being read at an "initially correct" measuring-rod, after it was introduced into the system and was accordingly deformed. T 0 are those time intervals indicated by an "initially ticking" clock, after it was inserted into the system and accordingly has changed its rate, he critically remarked that the distinction between "true time" and "local time" in Lorentz's theory is artificial, because it cannot be verified by experiment. However, Cohn himself believed that the validity of Lorentz's theory is limited to optical phenomena, whereas in his own theory it is possible that mechanical clocks might indicate the "true" time. In 1911, Cohn accepted