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Tetranucleotide Hypothesis
The tetranucleotide hypothesis of Phoebus Levene proposed that DNA was composed of repeating sequences of four nucleotides. It was very influential for three decades, and was developed by Levene at least into the 1910, and the diagram at the right illustrates the view of Levene and Tipson. In 1940, at the time of Levene's death, Bass wrote in his obituary As a result of Levene’s work we have an exact concept of the structures of these huge molecules, probably the most complex biological materials whose architectural picture has been reconstructed. In that form there is an implication that the four bases are present in equal amounts in DNA, and small variations in the experimental values were assumed to be the result of experimental error. However, Erwin Chargaff showed that the four frequencies were not equal, with variations consistent between different studies. Specifically, according to his rules Rule or ruling may refer to: Human activity * The exercise of politic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetranucleotide Unit
Nucleotides are organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules within all life-forms on Earth. Nucleotides are obtained in the diet and are also synthesized from common nutrients by the liver. Nucleotides are composed of three subunit molecules: a nucleobase, a five-carbon sugar (ribose or deoxyribose), and a phosphate group consisting of one to three phosphates. The four nucleobases in DNA are guanine, adenine, cytosine, and thymine; in RNA, uracil is used in place of thymine. Nucleotides also play a central role in metabolism at a fundamental, cellular level. They provide chemical energy—in the form of the nucleoside triphosphates, adenosine triphosphate (ATP), guanosine triphosphate (GTP), cytidine triphosphate (CTP), and uridine triphosphate (UTP)—throughout the cell for t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phoebus Levene
Phoebus Aaron Theodore Levene (25 February 1869 – 6 September 1940) was a Russian-born American biochemist who studied the structure and function of nucleic acids. He characterized the different forms of nucleic acid, DNA from RNA, and found that DNA contained adenine, guanine, thymine, cytosine, deoxyribose, and a phosphate group. He was born into a Litvak (Lithuanian Jewish) family as ''Fishel Aronovich Levin'' in the town of Žagarė in Lithuania, then part of the Russian Empire, but grew up in St. Petersburg. There he studied medicine at the Imperial Military Medical Academy (M.D., 1891) and developed an interest in biochemistry. In 1893, because of anti-Semitic pogroms, he and his family emigrated to the United States and he practiced medicine in New York City. Levene enrolled at Columbia University and in his spare time conducted biochemical research, publishing papers on the chemical structure of sugars. In 1896 he was appointed as an Associate in the Pathologic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromosome
A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most important of these proteins are the histones. Aided by chaperone proteins, the histones bind to and condense the DNA molecule to maintain its integrity. These eukaryotic chromosomes display a complex three-dimensional structure that has a significant role in transcriptional regulation. Normally, chromosomes are visible under a light microscope only during the metaphase of cell division, where all chromosomes are aligned in the center of the cell in their condensed form. Before this stage occurs, each chromosome is duplicated ( S phase), and the two copies are joined by a centromere—resulting in either an X-shaped structure if the centromere is located equatorially, or a two-armed structure if the centromere is located distally; the jo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Erwin Chargaff
Erwin Chargaff (11 August 1905 – 20 June 2002) was an Austro-Hungarian-born American biochemist, writer, and professor of biochemistry at Columbia University medical school. A Bucovinian Jew who immigrated to the United States during the Nazi Germany, Nazi regime, he penned a well-reviewed autobiography, ''Heraclitean Fire: Sketches from a Life Before Nature''. Through careful experimentation, Chargaff discovered two rules, called Chargaff's rules, which helped lead to the discovery of the double helix structure of DNA. Early life Chargaff was born on 11 August 1905 to a Jewish family in Czernowitz, Duchy of Bukovina, Austria-Hungary, which is now Chernivtsi, Ukraine. At the outbreak of World War I, his family moved to Vienna, where he attended the Maximiliansgymnasium (now the Gymnasium Wasagasse). He then went on to the TU Wien, Vienna College of Technology (''Technische Hochschule Wien'') where he met his future wife Vera Broido. From 1924 to 1928, Chargaff studied chemist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chargaff's Rules
Chargaff's rules (given by Erwin Chargaff) state that in the DNA of any species and any organism, the amount of guanine should be equal to the amount of cytosine and the amount of adenine should be equal to the amount of thymine. Further, a 1:1 stoichiometric ratio of purine and pyrimidine bases (i.e., A+G=T+C) should exist. This pattern is found in both strands of the DNA. They were discovered by Austrian-born chemist Erwin Chargaff in the late 1940s. Definitions First parity rule The first rule holds that a double-stranded DNA molecule, ''globally'' has percentage base pair equality: A% = T% and G% = C%. The rigorous validation of the rule constitutes the basis of Watson–Crick base pairs in the DNA double helix model. Second parity rule The second rule holds that both Α% ≈ Τ% and G% ≈ C% are valid for each of the two DNA strands. This describes only a global feature of the base composition in a single DNA strand. Research The second parity rule was discovered ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Biochemistry
Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, and metabolism. Over the last decades of the 20th century, biochemistry has become successful at explaining living processes through these three disciplines. Almost all List of life sciences, areas of the life sciences are being uncovered and developed through biochemical methodology and research.#Voet, Voet (2005), p. 3. Biochemistry focuses on understanding the chemical basis that allows biomolecule, biological molecules to give rise to the processes that occur within living Cell (biology), cells and between cells,#Karp, Karp (2009), p. 2. in turn relating greatly to the understanding of tissue (biology), tissues and organ (anatomy), organs as well as organism structure and function.#Miller, Miller (2012). p. 62. Biochemistry is closely ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecular Biology
Molecular biology is a branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, biomolecular synthesis, modification, mechanisms, and interactions. Though cells and other microscopic structures had been observed in living organisms as early as the 18th century, a detailed understanding of the mechanisms and interactions governing their behavior did not emerge until the 20th century, when technologies used in physics and chemistry had advanced sufficiently to permit their application in the biological sciences. The term 'molecular biology' was first used in 1945 by the English physicist William Astbury, who described it as an approach focused on discerning the underpinnings of biological phenomena—i.e. uncovering the physical and chemical structures and properties of biological molecules, as well as their interactions with other molecules and how these interactions explain observ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
History Of Genetics
The history of genetics dates from the classical era with contributions by Pythagoras, Hippocrates, Aristotle, Epicurus, and others. Modern genetics began with the work of the Augustinian friar Gregor Johann Mendel. Experiments on Plant Hybridisation, His works on pea plants, published in 1866, provided the initial evidence that, on its rediscovery in 1900's, helped to establish the theory of Mendelian inheritance. In ancient Greece, Hippocrates suggested that all organs of the body of a parent gave off invisible "seeds", miniaturised components that were transmitted during sexual intercourse and combined in the mother's womb to form a baby. In the early modern period, William Harvey's book ''On Animal Generation'' contradicted Aristotle's biology, Aristotle's theories of genetics and embryology. The 1900 rediscovery of Mendel's work by Hugo de Vries, Carl Correns and Erich von Tschermak led to rapid advances in genetics. By 1915 the basic principles of Mendelian genetics had b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleic Acids
Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). If the sugar is ribose, the polymer is RNA; if the sugar is deoxyribose, a variant of ribose, the polymer is DNA. Nucleic acids are chemical compounds that are found in nature. They carry information in cells and make up genetic material. These acids are very common in all living things, where they create, encode, and store information in every living cell of every life-form on Earth. In turn, they send and express that information inside and outside the cell nucleus. From the inner workings of the cell to the young of a living thing, they contain and provide information via the nucleic acid sequence. This gives the RNA and DNA their unmistakable 'ladder-step' order of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protein Structure
Protein structure is the three-dimensional arrangement of atoms in an amino acid-chain molecule. Proteins are polymers specifically polypeptides formed from sequences of amino acids, which are the monomers of the polymer. A single amino acid monomer may also be called a ''residue'', which indicates a repeating unit of a polymer. Proteins form by amino acids undergoing condensation reactions, in which the amino acids lose one water molecule per reaction in order to attach to one another with a peptide bond. By convention, a chain under 30 amino acids is often identified as a peptide, rather than a protein. To be able to perform their biological function, proteins fold into one or more specific spatial conformations driven by a number of non-covalent interactions, such as hydrogen bonding, ionic interactions, Van der Waals forces, and hydrophobic packing. To understand the functions of proteins at a molecular level, it is often necessary to determine their three-dimensiona ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Obsolete Scientific Theories
This list includes well-known general theories in science and pre-scientific natural philosophy and natural history that have since been superseded by other scientific theories. Many discarded explanations were once supported by a scientific consensus, but replaced after more empirical information became available that identified flaws and prompted new theories which better explain the available data. Pre-modern explanations originated before the scientific method, with varying degrees of empirical support. Some scientific theories are discarded in their entirety, such as the replacement of the phlogiston theory by energy and thermodynamics. Some theories known to be incomplete or in some ways incorrect are still used. For example, Newtonian classical mechanics is accurate enough for practical calculations at everyday distances and velocities, and it is still taught in schools. The more complicated relativistic mechanics must be used for long distances and velocities nearing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
