Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can grow as long as 50 micrometres and are dynamic; the outer diameter of a microtubule is between 23 and 27 nm while the inner diameter is between 11 and 15 nm. They are formed by the polymerization of a dimer of two globular proteins and beta tubulin into protofilaments that can associate laterally to form a hollow tube, the microtubule; the most common form of a microtubule consists of 13 protofilaments in the tubular arrangement. Microtubules are important in a number of cellular processes, they are involved in maintaining the structure of the cell and, together with microfilaments and intermediate filaments, they form the cytoskeleton. They make up the internal structure of cilia and flagella, they provide platforms for intracellular transport and are involved in a variety of cellular processes, including the movement of secretory vesicles and intracellular macromolecular assemblies.
They are involved in cell division and are the major constituents of mitotic spindles, which are used to pull eukaryotic chromosomes apart. Microtubules are nucleated and organized by microtubule organizing centers, such as the centrosome found in the center of many animal cells or the basal bodies found in cilia and flagella, or the spindle pole bodies found in most fungi. There are many proteins that bind to microtubules, including the motor proteins kinesin and dynein, microtubule-severing proteins like katanin, other proteins important for regulating microtubule dynamics. An actin-like protein has been found in a gram-positive bacterium Bacillus thuringiensis, which forms a microtubule-like structure called a nanotubule, involved in plasmid segregation. Other bacterial microtubules have a ring of five protofilaments. Tubulin and microtubule-mediated processes, like cell locomotion, were seen by early microscopists, like Leeuwenhoek. However, the fibrous nature of flagella and other structures were discovered two centuries with improved light microscopes, confirmed in the 20th century with the electron microscope and biochemical studies.
Microtubule in vitro assays for motor proteins such as dynein and kinesin are researched by fluorescently tagging a microtubule and fixing either the microtubule or motor proteins to a microscope slide visualizing the slide with video-enhanced microscopy to record the travel of the microtubule motor proteins. This allows the movement of the motor proteins along the microtubule or the microtubule moving across the motor proteins; some microtubule processes can be determined by kymograph. In eukaryotes, microtubules are long, hollow cylinders made up of polymerised α- and β-tubulin dimers; the inner space of the hollow microtubule cylinders is referred to as the lumen. The α and β-tubulin subunits are 50% identical at the amino acid level, each have a molecular weight of 50 kDa; these α/β-tubulin dimers polymerize end-to-end into linear protofilaments that associate laterally to form a single microtubule, which can be extended by the addition of more α/β-tubulin dimers. Microtubules are formed by the parallel association of thirteen protofilaments, although microtubules composed of fewer or more protofilaments have been observed in various species as well as in vitro.
Microtubules have a distinct polarity, critical for their biological function. Tubulin polymerizes end to end, with the β-subunits of one tubulin dimer contacting the α-subunits of the next dimer. Therefore, in a protofilament, one end will have the α-subunits exposed while the other end will have the β-subunits exposed; these ends are designated ends, respectively. The protofilaments bundle parallel to one another with the same polarity, so, in a microtubule, there is one end, the end, with only β-subunits exposed, while the other end, the end, has only α-subunits exposed. While microtubule elongation can occur at both the and ends, it is more rapid at the end; the lateral association of the protofilaments generates a pseudo-helical structure, with one turn of the helix containing 13 tubulin dimers, each from a different protofilament. In the most common "13-3" architecture, the 13th tubulin dimer interacts with the next tubulin dimer with a vertical offset of 3 tubulin monomers due to the helicity of the turn.
There are other alternative architectures, such as 11-3, 12-3, 14-3, 15-4, or 16-4, that have been detected at a much lower occurrence. Microtubules can morph into other forms such as helical filaments, which are observed in protist organisms like foraminifera. There are two distinct types of interactions that can occur between the subunits of lateral protofilaments within the microtubule called the A-type and B-type lattices. In the A-type lattice, the lateral associations of protofilaments occur between adjacent α and β-tubulin subunits. In the B-type lattice, the α and β-tubulin subunits from one protofilament interact with the α and β-tubulin subunits from an adjacent protofilament, respectively. Experimental studies have shown that the B-type lattice is the primary arrangement within microtubules. However, in most microtubules there is a seam in which tubulin subunits interact α-β; some species of Prosthecobacter contain microtubules. The structure of these bacterial microtubules is similar to that of eukaryotic microtubules, consisting of a hollow tube of protofilaments assembled from heterodimers of bacterial tubulin A and bacterial tubulin B
"Labels or Love" is a song by American singer-songwriter Fergie from the soundtrack for the motion picture Sex and the City. The song samples parts of the Sex and the City theme song; the song was released in Brazil on May 4, 2008 after an exclusive premiere on Jovem Pan FM, one of the major radio stations in Brazil. The song was sent to US and Australian radios on June 3, 2008; the song debuted at number 28 on the Australian ARIA Singles Chart, in its second week ascended into the top 20 and has peaked at number 15. In the UK, the single peaked only at number 56; the song was nominated for the People's Choice Awards for "Favorite Song From a Soundtrack", but lost to Mamma Mia! by Meryl Streep. A music video for the single was never issued owing to the song's poor performance; the song's instrumental serves as the opening theme for South Korean cosmetic surgery series "Let Me In". Australian CD Single"Labels or Love" - 3:52 "Labels or Love" - 4:18Australian Maxi Single"Labels or Love" - 3:52 "Labels or Love" - 4:03 "Sex & The City" - 1:30 Lyrics of this song at MetroLyrics
Jacques Decour, real name Daniel Decourdemanche, was a French writer and resistant, killed by the Nazis. Jacques Decour studied at the Lycée Carnot in the Lycée Pasteur in Neuilly-sur-Seine, he began his studies in law, after a few years changed his orientation and studied German literature and obtained his degree in this topic. In 1932, he was named professor of French in Prussia at a school in Magdeburg. There, he wrote his first book, which described the risks of nationalism and the "inadmissible myth of race"; this book caused scandal in France, public opinion refused to take account of the menacing signs coming from Germany. He moved to a school in Reims and joined the French young Communist movement, he moved to Tours and joined the Communist Party. In 1937, he became professor of German in Paris at the lycée Rollin. Due to demobilisation, he joined the resistance and created the magazines L'université libre in 1940 and La Pensée libre in 1941 which became the most important publications in occupied France.
In 1941, Decour became responsible for the Comité national des écrivains which published a new magazine the Lettres françaises but never got to see it, due to his arrest by the French police on 17 February 1942. Taken by the Germans, he was killed on 30 May 1942, one week after Georges Solomon. In the prison where he was waiting for his execution, he wrote a letter saying goodbye to those he loved. Resigned to his forthcoming death, he expressed the confidence of his youth, hoped that his sacrifice would not have been in vain. "Fondation de la Résistance | Actualités". Fondationresistance.com. Retrieved 18 May 2016. List of publications Le lycée Jacques-Decour during the Occupation