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Seleucus III Ceraunus

Seleucus III Soter, called Seleucus Ceraunus, was a ruler of the Hellenistic Seleucid Kingdom, the eldest son of Seleucus II Callinicus and Laodice II. His birth name was Alexander and he was named after his great uncle the Seleucid official Alexander. Alexander changed his name to Seleucus. After a brief reign of three years, during which he unsuccessfully continued his father's war in Asia Minor against Attalus I of Pergamon of Pergamum, Seleucus was assassinated in Anatolia by members of his army, his official byname Soter means "Saviour", while his nickname Ceraunus means "Thunderbolt"

Glycan

Not to be confused with glucan. The terms glycan and polysaccharide are defined by IUPAC as synonyms meaning "compounds consisting of a large number of monosaccharides linked glycosidically". However, in practice the term glycan may be used to refer to the carbohydrate portion of a glycoconjugate, such as a glycoprotein, glycolipid, or a proteoglycan if the carbohydrate is only an oligosaccharide. Glycans consist of O-glycosidic linkages of monosaccharides. For example, cellulose is a glycan composed of β-1,4-linked D-glucose, chitin is a glycan composed of β-1,4-linked N-acetyl-D-glucosamine. Glycans can be homo- or heteropolymers of monosaccharide residues, can be linear or branched. Glycans can be found attached to proteins as in proteoglycans. In general, they are found on the exterior surface of cells. O- and N-linked glycans are common in eukaryotes but may be found, although less in prokaryotes. N-Linked glycans are attached in the endoplasmic reticulum to the nitrogen in the side chain of asparagine in the sequon.

The sequon is an Asn-X-Ser or Asn-X-Thr sequence, where X is any amino acid except proline and the glycan may be composed of N-acetylgalactosamine, neuraminic acid, N-acetylglucosamine, fucose and other monosaccharides. In eukaryotes, N-linked glycans are derived from a core 14-sugar unit assembled in the cytoplasm and endoplasmic reticulum. First, two N-acetyl glucosamine residues are attached to dolichol monophosphate, a lipid, on the external side of the endoplasmic reticulum membrane. Five mannose residues are added to this structure. At this point, the finished core glycan is flipped across the endoplasmic reticulum membrane, so that it is now located within the reticular lumen. Assembly continues within the endoplasmic reticulum, with the addition of four more mannose residues. Three glucose residues are added to this structure. Following full assembly, the glycan is transferred en bloc by the glycosyltransferase oligosaccharyltransferase to a nascent peptide chain, within the reticular lumen.

This core structure of N-linked glycans, consists of 14 residues. Image: https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=glyco.figgrp.469 Dark squares are N-acetylglucosamine. Once transferred to the nascent peptide chain, N-linked glycans, in general, undergo extensive processing reactions, whereby the three glucose residues are removed, as well as several mannose residues, depending on the N-linked glycan in question; the removal of the glucose residues is dependent on proper protein folding. These processing reactions occur in the Golgi apparatus. Modification reactions may involve the addition of a phosphate or acetyl group onto the sugars, or the addition of new sugars, such as neuraminic acid. Processing and modification of N-linked glycans within the Golgi does not follow a linear pathway; as a result, many different variations of N-linked glycan structure are possible, depending on enzyme activity in the Golgi. N-linked glycans are important in proper protein folding in eukaryotic cells.

Chaperone proteins in the endoplasmic reticulum, such as calnexin and calreticulin, bind to the three glucose residues present on the core N-linked glycan. These chaperone proteins serve to aid in the folding of the protein that the glycan is attached to. Following proper folding, the three glucose residues are removed, the glycan moves on to further processing reactions. If the protein fails to fold properly, the three glucose residues are reattached, allowing the protein to re-associate with the chaperones; this cycle may repeat several times. If a protein fails to properly fold, it is excreted from the endoplasmic reticulum and degraded by cytoplasmic proteases. N-linked glycans contribute to protein folding by steric effects. For example, cysteine residues in the peptide may be temporarily blocked from forming disulfide bonds with other cysteine residues, due to the size of a nearby glycan. Therefore, the presence of a N-linked glycan allows the cell to control which cysteine residues will form disulfide bonds.

N-linked glycans play an important role in cell-cell interactions. For example, tumour cells make N-linked glycans; these are recognized by the CD337 receptor on Natural Killer cells as a sign that the cell in question is cancerous. Within the immune system the N-linked glycans on an immune cell's surface will help dictate that migration pattern of the cell, e.g. immune cells that migrate to the skin have specific glycosylations that favor homing to that site. The glycosylation patterns on the various immunoglobulins including IgE, IgM, IgD, IgE, IgA, IgG bestow them with unique effector functions by altering their affinities for Fc and other immune receptors. Glycans may be involved in "self" and "non self" discrimination, which may be relevant to the pathophysiology of various autoimmune diseases; the targeting of degradative lysosomal enzymes is accomplished by N-linked glycans. The modification of an N-linked glycan with a mannose-6-phosphate residue serves as a signal that the protein to which this glycan is attached should be moved to the lysosome.

This recognition and trafficking of lysosomal enzymes by the presence of mannose-6-phosphate is accomplished by two proteins: CI-MPR and CD-MPR. In eukaryotes, O-linked glycans are assembled one sugar at a time on a serine or threonine residue of a peptide chain in the Golgi apparatus. Unlik

Giant Canada goose

The giant Canada goose is the largest subspecies of Canada goose, weighing in at 5 kg. It is found in central North America; these geese were at one point considered extinct, but were rediscovered. The giant Canada goose is mistaken for the Moffitt's Canada goose. However, giant geese have both a larger bill to body size ratio. Another good identifier includes the black on the neck, which starts much farther up the neck than any other subspecies; the giant goose's white cheek patch is large, reaching the lower bill. Unlike other variants, the underbelly is pale. A less reliable identifier is the white forehead and eyebrows, which don't always occur and Moffitt's geese less have; the giant Canada goose is classified with the Moffitt's Canada goose, forming a singular subspecies. It is alongside the dusky Canada goose, the closest relative to the Hawaiian goose. In the 1950s, the giant Canada goose was declared extinct; however a small population in Rochester, Minnesota was rediscovered by biologists in 1962.

In recent years, the subspecies' numbers have been increasing and can be found in parks and other urban areas. It is thought that introduced populations of Canada geese in Europe are derived from B. c. maxima in addition to the nominate subspecies canadensis. Giant Canada goose Giant Canada Goose, Branta canadensis maxima, in Arizona Distinguishing Cackling and Canada Goose