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Deoxyribonucleic acid ( ; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses. DNA and ribonucleic acid (RNA) are nucleic acids. Alongside proteins, lipids and complex carbohydrates (polysaccharides), nucleic acids are one of the four major types of macromolecules that are essential for all known forms of life. The two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases (cytosine [C], guanine [G], adenine [A] or thymine [T]), a sugar called deoxyribose, and a phosphate group. The nucleotides are joined to one another in a chain by covalent bonds (known as the phosphodiester linkage) between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules (A with T and C with G), with hydrogen bonds to make double-stranded DNA. The complementary nitrogenous bases are divided into two groups, the single-ringed pyrimidines and the double-ringed purines. In DNA, the pyrimidines are thymine and cytosine; the purines are adenine and guanine. Both strands of double-stranded DNA store the same biological information. This information is replicated when the two strands separate. A large part of DNA (more than 98% for humans) is non-coding, meaning that these sections do not serve as patterns for protein sequences. The two strands of DNA run in opposite directions to each other and are thus antiparallel. Attached to each sugar is one of four types of nucleobases (or bases). It is the sequence of these four nucleobases along the backbone that encodes genetic information. RNA strands are created using DNA strands as a template in a process called transcription, where DNA bases are exchanged for their corresponding bases except in the case of thymine (T), for which RNA substitutes uracil (U). Under the genetic code, these RNA strands specify the sequence of amino acids within proteins in a process called translation. Within eukaryotic cells, DNA is organized into long structures called chromosomes. Before typical cell division, these chromosomes are duplicated in the process of DNA replication, providing a complete set of chromosomes for each daughter cell. Eukaryotic organisms (animals, plants, fungi and protists) store most of their DNA inside the cell nucleus as nuclear DNA, and some in the mitochondria as mitochondrial DNA or in chloroplasts as chloroplast DNA. In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm, in circular chromosomes. Within eukaryotic chromosomes, chromatin proteins, such as histones, compact and organize DNA. These compacting structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. Properties DNA is a long polymer made from repeating units called nucleotides. The structure of DNA is dynamic along its length, being capable of coiling into tight loops and other shapes. In all species it is composed of two helical chains, bound to each other by hydrogen bonds. Both chains are coiled around the same axis, and have the same pitch of 34 ångströms (3.4 nm). The pair of chains have a radius of 10 Å (1.0 nm). According to another study, when measured in a different solution, the DNA chain measured 22–26 Å (2.2–2.6 nm) wide, and one nucleotide unit measured 3.3 Å (0.33 nm) long. The buoyant density of most DNA is 1.7g/cm3. DNA does not usually exist as a single strand, but instead as a pair of strands that are held tightly together. These two long strands coil around each other, in the shape of a double helix. The nucleotide contains both a segment of the backbone of the molecule (which holds the chain together) and a nucleobase (which interacts with the other DNA strand in the helix). A nucleobase linked to a sugar is called a nucleoside, and a base linked to a sugar and to one or more phosphate groups is called a nucleotide. A biopolymer comprising multiple linked nucleotides (as in DNA) is called a polynucleotide. The backbone of the DNA strand is made from alternating phosphate and sugar groups. The sugar in DNA is 2-deoxyribose, which is a pentose (five-carbon) sugar. The sugars are joined by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings. These are known as the 3′-end (three prime end), and 5′-end (five prime end) carbons, the prime symbol being used to distinguish these carbon atoms from those of the base to which the deoxyribose forms a glycosidic bond. Therefore, any DNA strand normally has one end at which there is a phosphate group attached to the 5′ carbon of a ribose (the 5′ phosphoryl) and another end at which there is a free hydroxyl group attached to the 3′ carbon of a ribose (the 3′ hydroxyl). The orientation of the 3′ and 5′ carbons along the sugar-phosphate backbone confers directionality (sometimes called polarity) to each DNA strand. In a nucleic acid double helix, the direction of the nucleotides in one strand is opposite to their direction in the other strand: the strands are antiparallel. The asymmetric ends of DNA strands are said to have a directionality of five prime end (5′ ), and three prime end (3′), with the 5′ end having a terminal phosphate group and the 3′ end a terminal hydroxyl group. One major difference between DNA and RNA is the sugar, with the 2-deoxyribose in DNA being replaced by the related pentose sugar ribose in RNA. The DNA double helix is stabilized primarily by two forces: hydrogen bonds between nucleotides and base-stacking interactions among aromatic nucleobases. The four bases found in DNA are adenine (A), cytosine (C), guanine (G) and thymine (T). These four bases are attached to the sugar-phosphate to form the complete nucleotide, as shown for adenosine monophosphate. Adenine pairs with thymine and guanine pairs with cytosine, forming A-T and G-C base pairs. Nucleobase classification The nucleobases are classified into two types: the purines, A and G, which are fused five- and six-membered heterocyclic compounds, and the pyrimidines, the six-membered rings C and T. A fifth pyrimidine nucleobase, uracil (U), usually takes the place of thymine in RNA and differs from thymine by lacking a methyl group on its ring. In addition to RNA and DNA, many artificial nucleic acid analogues have been created to study the properties of nucleic acids, or for use in biotechnology. Non-canonical bases Modified bases occur in DNA. The first of these recognized was 5-methylcytosine, which was found in the genome of Mycobacterium tuberculosis in 1925. The reason for the pres.... Discover the Varios popular books. Find the top 100 most popular Varios books.
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Estudios varios de Derecho notarial
Leonardo Bernardino Pérez GallardoEl derecho notarial cubano se ha erigido en una de las materias que más cambios ha tenido en los últimos tiempos. La atribución acumulada de competencias ha sido galopante en aras ...
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Una vida en varios poemas
Pablo Prone¿Creés que es posible revelar nuestros mayores secretos y sentimientos mediante las palabras?¿Te sentiste en algún momento identificado con un poema?En Una vida en varios poemas, e...
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Mercurio Volante con noticias importantes y curiosas sobre varios asuntos de fisica y medicina
Josef Ignacio BartolacheMercurio Volante es una correspondencia con noticias importantes sobre varios asuntos de Fisica Medicina.
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Escritos varios
José Gervasio Artigas ArnalComprendio de: Proclama de Mercedes (1811) Parte de la Batalla de Las Piedras de José Artigas a José Rondeau (1811) El discurso de Tres Cruces (1813) Reglamento Provisorio de la Pr...
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Estudios oratorios u observaciones criticas sobre oradores mas clasicos
Clemente MunguiaDiscursos de los más clásicos oradores, arengas y observaciones críticas, por Clemente Munguia. Morelia, 1841.
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Poemas Varios
Fausto Hernando Canto GarciaColección de 10 poemas sobre diversas situaciones personales del autor; desde la despedida de un familiar, hasta la ilusión de un nuevo amor, el lector facilmente se apropiará de e...
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Articulos varios
Gustavo Adolfo BécquerPequeño compendio de artículos varios del escritor Gustavo Adolfo Bécquer aparecidos en diferentes periódicos d ela época, permiten observar una faceta poco conocida de este escrit...
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De varios colores
Juan ValeraCon siglos de literatura, es inevitable que algunos pasen desapercibidos. Buscamos obras de dominio público y las restauramos para que no se pierdan en el mundo. ¿Quiénes somos? S...
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Con la Venia, Manual de oratoria para abogados
Óscar Fernández LeónEn un ordenamiento jurídico como el español, en cuyos procesos judiciales prevalece el principio de oralidad, el conocimiento, el aprendizaje y la puesta en práctica de las normas ...
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De varios colores
Juan ValeraBREVES HISTORIAS. GARUDA O LA CIGÜEÑA BLANCA. EL CAUTIVO DE DOÑA MENCÍA. EL MAESTRO RAIMUNDICO. CUENTOS JAPONESES. UN DRAMA TRÁGICO.
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De varios colores
Juan ValeraNo todas las flores son frescas y bonitas; también las hay mustias y feas. No se me culpe, pues, de presumido, si valiéndome de una figura retórica llamo flores de mi pobre y agost...
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Floresta de varios romances
Various AuthorsO romance de Dom Duardos, composto por Gil Vicente, foi recolhido no Cancionero de Romances como anonymo, e assim a historia dos amores de Bernardim Ribeiro. Na ...
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Historia del Opus Dei
José Luis González Gullón & John F. CoverdaleDesde hace un siglo, el Opus Dei irradia en el mundo un mensaje de encuentro con Dios en la vida corriente. No es poco lo que se ha escrito sobre esta institución y sobre su fundad...
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Cuentos Varios
Vicente Blasco IbáñezColección de relatos del autor Vicente Blasco Ibáñez. En ellos, el escritor realiza un certero análisis de la situación social y política de la España de su época, siempre vista de...
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Cuentos varios
Vicente Blasco IbáñezRecopilación de cuentos aparecidos en diferentes antologías.Al lectorCompasiónEl amor y la muerteLa vejezLa Madre TierraRosas y ruisenores
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Cuentos varios
Vicente Blasco IbáñezRecopilación de cuentos aparecidos en diferentes antologías. Al lector Compasión El amor y la muerte La vejez La Madre Tierra Rosas y ruiseñores
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Guerra civil de 1876 o guerra de las escuelas Autores varios
Ediciones LAVPLa guerra civil de 1876 también denominada como “La revolución conservadora de 1876” o “La guerra de los curas”, o “guerra de las escuelas” se inició en el Estado del Cauca en el m...
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Consulta que el C. Lic. Ignacio L. Vallarta y otros varios letrados dan al C. Fermin Gomez Farias
D. Jose Maria MendozaConsulta de Ignacio L. Vallarta en defensa de C. Manuel de la Pedreguera, con motivo del despojo de las Salinas de Cuyutlán, dictado por el prefecto de Colima D. José Maria Mendoza...
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De varios colores
Juan ValeraJuan Valera y Alcalá Galiano; Cabra, 1824 Madrid, 1905) Escritor y crítico español cuya obra se inscribe en una corriente esteticista opuesta al realismo naturalista. Político y d...
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Recopilacion de cuentos varios
Leopoldo AlasRecopilación de cuentos varios: El doctor Pértinax De la comisión Doctor Angelicus Medalla... de perro chico Un candidato Un repatriado Doble vía Cuesta abajo El oso mayor Tambor y...