query: Who discovered the structure of DNA?

title: Non-helical models of DNA structure

text: the top of this article, or there could be an equal number of right-handed and left-handed twists, as in the Rodley structure below. The abbreviation "TN", to be used to refer to any DNA structure whose strands are topologically non-linked, has been proposed. The double-helix model of DNA structure was first published in the journal "Nature" by James D. Watson and Francis Crick in 1953 with further details in 1954.) Their work was based upon the crucial X-ray diffraction image of DNA - labeled as "Photo 51" - from Rosalind Franklin in 1952, followed by her more highly clarified DNA

title: Non-helical models of DNA structure

text: Natural Science, 7, (5), 85-100, 2018. The discovery of topoisomerases, enzymes that can change the linking number of circular nucleic acids and thus "unwind" the replicating bacterial chromosome, was largely seen by the mainstream scientific community to satisfy the topological objection to the Watson–Crick helical structure. The later X-ray crystallography data for the nucleosome, which showed a helical DNA structure wrapped around the protein nucleosome core particle, was considered to provide further affirmation for the existence of the helical structure "in vivo". Non-double-helical models are not currently accepted by the mainstream scientific community. Enzymes capable of unwinding and rewinding DNA

title: Non-helical models of DNA structure

text: The SBS structure was hypothetical, and was not based primarily upon physical evidence. It was created to provide a theoretical solution to the angular momentum problem in DNA replication, which Rodley believed to be otherwise unsolvable. The SBS structure is a modification of the original Watson-Crick structure where, instead of one fully right-handed helical twist every 10 base pairs, there is only a "half"-twist of 5 base pairs’ length, followed immediately by a half-twist in the "opposite" direction (that is, a left-handed half-twist, also of 5 base pairs’ length). This alternating pattern of right- and left-handed half-twists is repeated throughout

title: Non-helical models of DNA structure

text: image with Raymond Gosling, Maurice Wilkins, Alexander Stokes, and Herbert Wilson, as well as base-pairing chemical and biochemical information by Erwin Chargaff. Wilkins and colleagues also reported on X-ray patterns of the state of "in vivo" B-DNA in partially oriented salmon sperm heads. Crick, Wilkins, and Watson each received one-third of the 1962 Nobel Prize in Physiology or Medicine for their contributions to this discovery. Franklin, whose breakthrough X-ray diffraction data was used to formulate the DNA structure, died in 1958, and thus was ineligible to be nominated for a Nobel Prize. In 1963, John Cairns published autoradiographs of the

title: Non-helical models of DNA structure

text: as evidence that the strands were plectonemically wound together ("i.e.," topologically linked). The publication of the Rodley structure produced a small but significant ripple of interest in the molecular biological community. However, the level of interest was sufficiently high so that Crick - by that time one of the world’s most influential scientists - publicly suggested that the SBS structure (whose existence he doubted) should be laid to rest by intentionally creating it. Then, he reasoned, its properties could be ascertained, and then shown to be abnormal with respect to the known properties of native DNA. An investigation by Stettler

title: Non-helical models of DNA structure

text: have about 400,000 helical twists in the Watson–Crick model, each of which would have to be removed in as little as 20 minutes, if the strands are to separate during cell replication. This leads to the apparent need of the chromosome - or at least some part of it - to be spinning at speeds up to 6900–9000 rpm throughout the life of the bacterial cell. In 1976, Gordon Rodley and his co-workers published the first non-helical DNA structure, which they named the "side-by-side" (SBS) structure. A similar model was published a few months later by Sasisekharan and his associates.

title: Eukaryotic chromosome structure

text: fold and pack the fine thread of DNA into a more compact structure. The nucleosome consists of a DNA double helix bound to an octamer of core histones (2 dimers of H2A and H2B, and an H3/H4 tetramer). About 147 base pairs of DNA coil around 1 octamer, and ~20 base pairs are sequestered by the addition of the linker histone (H1), and various length of "linker" DNA (~0-100 bp) separate the nucleosomes. The double helix was discovered in 1953 by James Watson and Francis Crick. Other researchers made very important, but unconnected findings about the composition of DNA. But

title: Non-helical models of DNA structure

text: "et al". followed closely on the heels of the Crick suggestion. They isolated the intact circular single strands of a circular duplex viral chromosome and then re-annealed them, giving a product they declared to be a "base-paired circular duplex with no net helical twist". If so, this would in fact be the Rodley "side-by-side" structure. They introduced a new terminology for this product, calling it "Form V" (extending the nomenclature of Forms I–IV used in sedimentation studies of DNA), and then went on to demonstrate that its electrophoretic mobility was clearly different from that of the native chromosome. The results

title: DNA Tower

text: The glass is held in place by a steel armature that is painted blue. The base support of the sculpture is surrounded and protected by a 5' tall circular cherry wood base that is 5'5" in diameter. "DNA Tower" was commissioned to commemorate both the 100th anniversary of the IU School of Medicine (founded 1903) and the 50th anniversary of the discovery of the structure of the DNA molecule (discovered 1953) by 1950 IU alumnus James D. Watson and his colleague Francis Crick. The glass pieces and painted steel armature were fabricated in Chihuly's Seattle studios. On September 23, 2003,

title: DNA

text: archaea) store their DNA only in the cytoplasm. Within eukaryotic chromosomes, chromatin proteins, such as histones, compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. DNA was first isolated by Friedrich Miescher in 1869. Its molecular structure was first identified by James Watson and Francis Crick at the Cavendish Laboratory within the University of Cambridge in 1953, whose model-building efforts were guided by X-ray diffraction data acquired by Raymond Gosling, who was a post-graduate student of Rosalind Franklin. DNA is used by researchers as a

title: Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid

text: interests in particular. Crick, Watson, and Maurice Wilkins who won the Nobel Prize for Medicine in recognition of their discovery of the DNA double helix. It is not always the case that the structure of a molecule is easy to relate to its function. What makes the structure of DNA so obviously related to its function was described modestly at the end of the article: "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material". The "specific pairing" is a key feature of the Watson and Crick

title: Logology (science of science)

text: Linus Pauling discovered the chemical structure of protein and proposed a completely wrong structure for DNA, which carries hereditary information from parent to offspring. Pauling guessed a wrong structure for DNA because he assumed that a pattern that worked for protein would also work for DNA. He overlooked the gross chemical differences between protein and DNA. Francis Crick and James Watson paid attention to the differences and found the correct structure for DNA that Pauling had missed a year earlier. Astronomer Fred Hoyle discovered the process by which the heavier elements essential to life are created by nuclear reactions in

title: Molecular models of DNA

text: simulations that are very important to understand how DNA functions "in vivo". From the very early stages of structural studies of DNA by X-ray diffraction and biochemical means, molecular models such as the Watson-Crick nucleic acid double helix model were successfully employed to solve the 'puzzle' of DNA structure, and also find how the latter relates to its key functions in living cells. The first high quality X-ray diffraction patterns of A-DNA were reported by Rosalind Franklin and Raymond Gosling in 1953. Rosalind Franklin made the critical observation that DNA exists in two distinct forms, A and B, and produced

text: from 1953 to 1965. Francis Crick played an integral role in both the theory and analysis of the experiments that led to an improved understanding of the genetic code. Other advances in molecular biology stemming from the discovery of the DNA double helix eventually led to ways to sequence genes. James Watson directed the Human Genome Project at the National Institutes of Health. The ability to sequence and manipulate DNA is now central to the biotechnology industry and modern medicine. The austere beauty of the structure and the practical implications of the DNA double helix combined to make "Molecular structure

title: DNA

text: of DNA. An alternative analysis was then proposed by Wilkins "et al.", in 1953, for the "in vivo" B-DNA X-ray diffraction-scattering patterns of highly hydrated DNA fibers in terms of squares of Bessel functions. In the same journal, James Watson and Francis Crick presented their molecular modeling analysis of the DNA X-ray diffraction patterns to suggest that the structure was a double-helix. Although the "B-DNA form" is most common under the conditions found in cells, it is not a well-defined conformation but a family of related DNA conformations that occur at the high hydration levels present in living cells. Their

title: Nucleic acid tertiary structure

text: new RNA and DNA molecules are structurally characterized. The double helix is the dominant tertiary structure for biological DNA, and is also a possible structure for RNA. Three DNA conformations are believed to be found in nature, A-DNA, B-DNA, and Z-DNA. The "B" form described by James D. Watson and Francis Crick is believed to predominate in cells. James D. Watson and Francis Crick described this structure as a double helix with a radius of 10 Å and pitch of 34 Å, making one complete turn about its axis every 10 bp of sequence. The double helix makes one complete

title: Non-helical models of DNA structure

text: helical DNA duplex, if covalently closed into a circular structure, are topologically linked, and thus cannot be separated without breaking one or both strands. This sort of structure is referred to as "plectonemic". In circular DNA replication, these twists must be removed for the daughter strands to separate. In contrast, the strands of a non-helical DNA duplex would be topologically non-linked, and can be separated without strand breakage. This sort of structure is referred to as "paranemic". Note that the term "non-helical" refers to "net" helicity - there can be no helical twist at all, as in the figure at

title: Non-helical models of DNA structure

text: of this investigation were not accepted by some authors, who agreed that it was established satisfactorily that "Form V" is different from native DNA, but did not establish that "Form V" has the SBS structure. While the strands of native circular DNA are known not to be separable under common denaturing conditions, in 1996, following his earlier theoretical studies in 1969, Tai Te Wu reported having found conditions under which fully intact single strands of two different circular duplex plasmids could be separated. Wu believed that, because these plasmids have D-loops with DNA–RNA duplexes from RNA transcription only on their

title: Rosalind Franklin and DNA

text: Rosalind Franklin and DNA Rosalind Franklin and DNA is a biography of an English chemist Rosalind Franklin (1920–1958) written by her American friend Anne Sayre in 1975. Franklin was a physical chemist who made pivotal research in the discovery of the structure of DNA, known as "the most important discovery" in biology. DNA itself had become "life's most famous molecule". While working at the King's College London in 1951, she discovered two types of DNA called A-DNA and B-DNA. Her X-ray images of DNA indicated helical structure. Her X-ray image of B-DNA (called Photo 51) taken in 1952 became the

title: A-DNA

text: A-DNA A-DNA is one of the possible double helical structures which DNA can adopt. A-DNA is thought to be one of three biologically active double helical structures along with B-DNA and Z-DNA. It is a right-handed double helix fairly similar to the more common B-DNA form, but with a shorter, more compact helical structure whose base pairs are not perpendicular to the helix-axis as in B-DNA. It was discovered by Rosalind Franklin, who also named the A and B forms. She showed that DNA is driven into the A form when under dehydrating conditions. Such conditions are commonly used to

title: Non-helical models of DNA structure

text: helical twists, namely topoisomerases and gyrases, are essential for life, and necessary for DNA replication in various "in vitro" synthesis systems. Non-helical models of DNA structure In the history of molecular biology, non-helical or "side-by-side" models of DNA were proposed in the 1970s as a challenge to the standard double-helical model. The non-helical models attempted to solve problems relating to the topology of circular DNA chromosomes during replication. These theories were briefly considered seriously as a minority viewpoint, but they were later largely rejected due to X-ray crystallography of DNA duplexes and later the nucleosome core particle, as well as

title: Theta structure

text: Theta structure A Theta structure is an intermediate structure formed during the replication of a circular DNA molecule (prokaryote DNA). Two replication forks can proceed independently around the DNA ring and when viewed from above the structure resembles the Greek letter "theta" (θ). Originally discovered by John Cairns, it led to the understanding that (in this case) bidirectional DNA replication could take place. Proof of the bidirectional nature came from providing replicating cells with a pulse of tritiated thymidine, quenching rapidly and then autoradiographing. Results showed that the radioactive thymidine was incorporated into both forks of the theta structure, not

title: Non-helical models of DNA structure

text: Non-helical models of DNA structure In the history of molecular biology, non-helical or "side-by-side" models of DNA were proposed in the 1970s as a challenge to the standard double-helical model. The non-helical models attempted to solve problems relating to the topology of circular DNA chromosomes during replication. These theories were briefly considered seriously as a minority viewpoint, but they were later largely rejected due to X-ray crystallography of DNA duplexes and later the nucleosome core particle, as well as the discovery of topoisomerases, and these non-double-helical models are not currently accepted by the mainstream scientific community. The strands of a

title: Solenoid (DNA)

text: than nucleosomes, whilst prokaryotes package their DNA through supercoiling. Solenoid (DNA) The solenoid structure of chromatin is a model for the structure of the 30 nm fibre. It is a secondary chromatin structure which helps to package eukaryotic DNA into the nucleus. Chromatin was first discovered by Walther Flemming by using aniline dyes to stain it. In 1974, it was first proposed by Roger Kornberg that chromatin was based on a repeating unit of a histone octamer and around 200 base pairs of DNA. The solenoid model was first proposed by John Finch and Aaron Klug in 1976. They used

title: Theta structure

text: just one, indicating synthesis at both forks in opposite directions around the loop. Theta structure A Theta structure is an intermediate structure formed during the replication of a circular DNA molecule (prokaryote DNA). Two replication forks can proceed independently around the DNA ring and when viewed from above the structure resembles the Greek letter "theta" (θ). Originally discovered by John Cairns, it led to the understanding that (in this case) bidirectional DNA replication could take place. Proof of the bidirectional nature came from providing replicating cells with a pulse of tritiated thymidine, quenching rapidly and then autoradiographing. Results showed that

title: Non-helical models of DNA structure

text: thymus DNA (a heterogeneous collection of linear fragments) is merely boiled, the strands separate, and when slowly cooled, they re-anneal. In contrast, when the circular chromosomes of such organisms as the replicative form (RF) of the bacteriophage φX174, or the mammalian virus polyoma, are boiled, nothing at all happens to the native structure - they are completely resistant to thermal denaturation. Without a doubt, the single most skepticism-inspiring aspect of non-helical DNA theory was the failure of the strands of circular chromosomes to separate under conditions where the strands of linear DNA would readily do so. This was generally regarded

title: Non-helical models of DNA structure

text: the length of the chromosome which, topologically speaking, would have no net twists. Such a chromosome does not need to either spin or unwind during replication. Rodley in later published work makes it clear that it was not the intention of his team that the model utilized alternating half turns of opposite helical sense, but lengths of DNA having alternating helical senses deployed in the available space along the DNA molecule that would not exactly be half turns. One key observation in support of a double-helical structure is that the individual single strands of small circular viral and plasmid DNA

title: Solenoid (DNA)

text: Solenoid (DNA) The solenoid structure of chromatin is a model for the structure of the 30 nm fibre. It is a secondary chromatin structure which helps to package eukaryotic DNA into the nucleus. Chromatin was first discovered by Walther Flemming by using aniline dyes to stain it. In 1974, it was first proposed by Roger Kornberg that chromatin was based on a repeating unit of a histone octamer and around 200 base pairs of DNA. The solenoid model was first proposed by John Finch and Aaron Klug in 1976. They used electron microscopy images and X-ray diffraction patterns to determine

title: Z-DNA

text: Z-DNA Z-DNA is one of the many possible double helical structures of DNA. It is a left-handed double helical structure in which the helix winds to the left in a zigzag pattern (instead of to the right, like the more common B-DNA form). Z-DNA is thought to be one of three biologically active double-helical structures along with A- and B-DNA. Left-handed DNA was first discovered by Robert Wells and colleagues, during their studies of a repeating polymer of inosine–cytosine. They observed a "reverse" circular dichroism spectrum for such DNAs, and interpreted this (correctly) to mean that the strands wrapped around

title: Z-DNA

text: cells are caused by non-homologous end-joining repair, which is known to be prone to error. The toxic effect of ethidium bromide (EtBr) on trypanosomas is caused by shift of their kinetoplastid DNA to Z-form. The shift is caused by intercalation of EtBr and subsequent loosening of DNA structure that leads to unwinding of DNA, shift to Z-form and inhibition of DNA replication. The first domain to bind Z-DNA with high affinity was discovered in ADAR1 using an approach developed by Alan Herbert. Crystallographic and NMR studies confirmed the biochemical findings that this domain bound Z-DNA in a non-sequence-specific manner. Related

title: Z-DNA

text: domains were identified in a number of other proteins through sequence homology. The identification of the Zα domain provided a tool for other crystallographic studies that lead to the characterization of Z-RNA and the B–Z junction. Biological studies suggested that the Z-DNA binding domain of ADAR1 may localize this enzyme that modifies the sequence of the newly formed RNA to sites of active transcription. As Z-DNA has been researched more thoroughly, it has been discovered that the structure of Z-DNA can bind to Z-DNA binding proteins through london dispersion and hydrogen bonding. One example of a Z-DNA binding protein is

title: DNA ligase

text: of DNA ligase can impede adjuvant cancer forms. Furthermore, it has been shown that DNA ligase can be broadly divided into two categories namely, ATP dependent and NAD+ dependent. Previous research has shown that although NAD-dependent DNA ligases have been discovered in sporadic cellular or viral niches outside the bacterial domain of life, there is no instance in which a NAD-dependent ligase is present in a eukaryal organism. The narrow phylogenetic distribution, unique substrate specificity, and distinctive domain structure of NAD+ depandant compared with ATP-dependent human DNA ligases recommend the NAD ligases as targets for the development of new antibacterial

title: DNA ligase

text: foil, DNA ligase can provide the enzymatic assistance that is required to make DNA lattice structure from DNA over hangs. The first DNA ligase was purified and characterized in 1967 by the Gellert, Lehman, Richardson, and Hurwitz laboratories. It was first purified and characterized by Weiss and Richardson using a six-step chromatographic-fractionation process beginning with elimination of cell debris and addition of streptomycin, followed by several Diethylaminoethyl (DEAE)-cellulose column washes and a final phosphocellulose fractionation. The final extract contained 10% of the activity initially recorded in the "E. coli "media; along the process it was discovered that ATP and Mg++

title: Non-helical models of DNA structure

text: sense side, and since DNA–RNA interactions are stronger than DNA–DNA interactions, the sense and anti-sense strands would thus have different electrophoretic mobilities. He employed a very low voltage, so that the electrophoresis required 48 hours to go to completion. DNA sequencing then indicated that each of the two bands were enriched in one of the two strands of the chromosome. Separately, the Stetter "et al". experiment was revisited in 2009 by Youcheng Xu, who noted that brief re-annealing times ("i.e." 20–30 minutes) resulted in anomalous structures which did not co-migrate with routinely prepared DNA topoisomers, while prolonged re-annealing times (in

title: DNA unwinding element

text: DNA unwinding element A DNA unwinding element (DUE or DNAUE) is the initiation site for the opening of the double helix structure of the DNA at the origin of replication for DNA synthesis. It is A-T rich and denatures easily due to its low helical stability, which allows the single-strand region to be recognized by origin recognition complex. DUEs are found in both prokaryotic and eukaryotic organisms, but were first discovered in yeast and bacteria origins, by Huang Kowalski. The DNA unwinding allows for access of replication machinery to the newly single strands. In eukaryotes, DUEs are the binding site

title: DNA nanotechnology

text: thirty years after he had set out to achieve it. New abilities continued to be discovered for designed DNA structures throughout the 2000s. The first DNA nanomachine—a motif that changes its structure in response to an input—was demonstrated in 1999 by Seeman. An improved system, which was the first nucleic acid device to make use of toehold-mediated strand displacement, was demonstrated by Bernard Yurke the following year. The next advance was to translate this into mechanical motion, and in 2004 and 2005, several DNA walker systems were demonstrated by the groups of Seeman, Niles Pierce, Andrew Turberfield, and Chengde Mao.

text: consequences of biological information from DNA to proteins. The discovery of the DNA double helix made clear that genes are functionally defined parts of DNA molecules, and that there must be a way for cells to translate the information in DNA to specific amino acids, which are used in order to make proteins. Linus Pauling was a chemist who was very influential in developing an understanding of the structure of biological molecules. In 1951, Pauling published the structure of the alpha helix, a fundamentally important structural component of proteins. In early 1953, Pauling published a triple helix model of DNA,

title: I-motif DNA

text: genomes, suggesting that C-rich tracts have a biological function. Furthermore, many proteins and ligands fundamental to gene expression recognize C-rich oligonucleotides, such as Poly-C-binding protein (PCBP) and heterogeneous nuclear ribonucleoprotein K (HNRPK). Until recently it was not clear whether I-motifs naturally existed in DNA due to their low stability at physiological pH; i-motifs were discovered in vivo in human DNA in 2018. Human telomeric DNA (hTelo) can form an i-motif secondary structure in vitro. Zeraati et. al. confirmed the presence of i-motif hTelo in human DNA using a fluorescent marker called iMab. Furthermore, i-motif hTelo was found within regulatory regions

title: Z-DNA

text: one another in a left-handed fashion. The relationship between Z-DNA and the more familiar B-DNA was indicated by the work of Pohl and Jovin, who showed that the ultraviolet circular dichroism of poly(dG-dC) was nearly inverted in 4 M sodium chloride solution. The suspicion that this was the result of a conversion from B-DNA to Z-DNA was confirmed by examining the Raman spectra of these solutions and the Z-DNA crystals. Subsequently, a crystal structure of "Z-DNA" was published which turned out to be the first single-crystal X-ray structure of a DNA fragment (a self-complementary DNA hexamer d(CG)). It was resolved

title: Molecular models of DNA

text: its structure, are a significant problem for cells. Every process which binds or reads DNA is able to use or modify the mechanical properties of DNA for purposes of recognition, packaging and modification. The extreme length (a chromosome may contain a 10 cm long DNA strand), relative rigidity and helical structure of DNA has led to the evolution of histones and of enzymes such as topoisomerases and helicases to manage a cell's DNA. The properties of DNA are closely related to its molecular structure and sequence, particularly the weakness of the hydrogen bonds and electronic interactions that hold strands of

title: Molecular models of DNA

text: in principle obtainable through 2D-FT NMR spectroscopy and relaxation studies of polynucleotide solutions or specifically labeled DNA, as for example with deuterium labels. In an interesting twist of roles, the DNA molecule was proposed to be used for quantum computing via DNA. Both DNA nanostructures and DNA computing biochips have been built. The chemical structure of DNA is insufficient to understand the complexity of the 3D structures of DNA. In contrast, animated molecular models allow one to visually explore the three-dimensional (3D) structure of DNA. The DNA model shown (far right) is a space-filling, or CPK, model of the DNA

title: Non-helical models of DNA structure

text: are inseparable under the usual types of denaturation conditions, supporting a plectonemic, "i.e.," twisted structure whose strands are topologically locked together. While human and bacterial chromosomes are far too large to isolate intact, but rather break into innumerable small fragments when extracted from their respective cells, there exist many species of small viral and plasmid chromosomes which because of their small sizes are stable in solution, and remain intact even with vigorous handling. Early studies quickly revealed that the strands of duplex circular chromosomes "do not separate" when subjected to conditions which readily denature linear DNA. For example, if calf

title: Non-helical models of DNA structure

text: "E. coli" chromosome, showing that it was a single circular molecule that is replicated at a moving locus - the "replication fork" - at which both new DNA strands are being synthesized. Cairns, at that time, recognized a topological problem in that the helical twists between the daughter strands would have to be removed if the strands are to separate during cell replication. He proposed that the twists were unwound by means of a hypothetical "swivel" around which the chromosome would be free to rotate as necessary for the un-winding and re-winding operations. However, such a structure would have to

title: DNA oxidation

text: level of oxidative stress that a cell endures is reflected by the quantity of reactive oxygen species (ROS). ROS are generated from normal oxygen metabolism in cells and are recognized as a list of active molecules, such as O, O, HO and, •OH . A nucleic acid can be oxidized by ROS through a Fenton reaction. To date, around 20 oxidative lesions have been discovered in DNA. RNAs are likely to be more sensitive to ROS for the following reasons: i) the basically single-stranded structure exposes more sites to ROS; ii) compared with nuclear DNA, RNAs are less compartmentalized; iii)

title: DNA-SCARS

text: discovered by Judith Campisi and colleagues, who first described them in 2011, although most of their characteristics were previously known. DNA-SCARS DNA-SCARS (short for DNA segments with chromatin alterations reinforcing senescence) are nuclear substructures with persistent DNA damage and DNA damage response proteins found in senescent cells. DNA-SCARS are associated with PML nuclear bodies and the accumulation of activated ATM, ATR, CHK2 and p53 proteins. DNA-SCARS lack most of the characteristics of transient, reversible DNA damage foci, such as single-stranded DNA, active DNA synthesis, and DNA repair proteins RPA and RAD51. Telomere dysfunction-induced foci (TIF) are generally associated with DNA-SCARS.

title: DNA

text: functions of DNA depend on interactions with proteins. These protein interactions can be non-specific, or the protein can bind specifically to a single DNA sequence. Enzymes can also bind to DNA and of these, the polymerases that copy the DNA base sequence in transcription and DNA replication are particularly important. Structural proteins that bind DNA are well-understood examples of non-specific DNA-protein interactions. Within chromosomes, DNA is held in complexes with structural proteins. These proteins organize the DNA into a compact structure called chromatin. In eukaryotes, this structure involves DNA binding to a complex of small basic proteins called histones, while

title: Kileak: The DNA Imperative

text: found in the South Base that a creature named "Kileak" is the first lifeform to have appeared on Earth, and the progenitor of all life on the planet. Kim found Kileak's DNA from an unknown pyramidal structure in the excavation pit, and used it to genetically engineer a race of mutant creatures. In other recordings, Byflos confronted Dr. Kim over his use of Kileak's DNA, and hid an "erosion gun" in his office for anyone who can stop Kim. As Dr. Kim plans to use an intercontinental ballistic missile (ICBM) to spread the mutant DNA all over the planet, Coda

title: DNA database

text: to be possible. While other siblings (including fraternal twins) share about 50% of their DNA, monozygotic twins share virtually 99.99%. Beyond these more recently discovered twinning-event mutation disparities, since 2008 it has been known that people who are identical twins also each have their own set of copy number variants, which can be thought of as the number of copies they each personally exhibit for certain sections of DNA. DNA database A DNA database or DNA databank is a database of DNA profiles which can be used in the analysis of genetic diseases, genetic fingerprinting for criminology, or genetic genealogy.

title: Eukaryotic DNA replication

text: leading-strand synthesis... DNA polymerases require additional factors to support DNA replication. DNA polymerases have a semiclosed 'hand' structure, which allows the polymerase to load onto the DNA and begin translocating. This structure permits DNA polymerase to hold the single-stranded DNA template, incorporate dNTPs at the active site, and release the newly formed double-stranded DNA. However, the structure of DNA polymerases does not allow a continuous stable interaction with the template DNA. To strengthen the interaction between the polymerase and the template DNA, DNA sliding clamps associate with the polymerase to promote the processivity of the replicative polymerase. In eukaryotes, the

title: Z-DNA

text: cations (all at physiological temperature, 37 °C, and pH 7.3–7.4). Z-DNA can form a junction with B-DNA (called a "B-to-Z junction box") in a structure which involves the extrusion of a base pair. The Z-DNA conformation has been difficult to study because it does not exist as a stable feature of the double helix. Instead, it is a transient structure that is occasionally induced by biological activity and then quickly disappears. It is possible to predict the likelihood of a DNA sequence forming a Z-DNA structure. An algorithm for predicting the propensity of DNA to flip from the B-form to

title: Recombinant DNA

text: two strands. Recombinant DNA is possible because DNA molecules from all organisms share the same chemical structure, and differ only in the nucleotide sequence within that identical overall structure. Recombinant DNA molecules are sometimes called chimeric DNA, because they can be made of material from two different species, like the mythical chimera. R-DNA technology uses palindromic sequences and leads to the production of sticky and blunt ends. The DNA sequences used in the construction of recombinant DNA molecules can originate from any species. For example, plant DNA may be joined to bacterial DNA, or human DNA may be joined with

title: Molecular models of DNA

text: DNA nanostructures designed for DNA computing and other dynamic applications of DNA nanotechnology. The image at right is of self-assembled DNA nanostructures. The DNA "tile" structure in this image consists of four branched junctions oriented at 90° angles. Each tile consists of nine DNA oligonucleotides as shown; such tiles serve as the primary "building block" for the assembly of the DNA nanogrids shown in the AFM micrograph. Quadruplex DNA may be involved in certain cancers. Images of quadruplex DNA are in the gallery below. Molecular models of DNA Molecular models of DNA structures are representations of the molecular geometry and

title: Crosslinking of DNA

text: and protein is a requirement to fully understand the biochemical processes. The structure of DNA-protein complexes can be mapped by photocrosslinking, which is the photoinduced formation of a covalent bond between two macromolecules or between two different parts of one macromolecule. The methodology involves covalently linking a DNA-binding motif of the target sequence-specific DNA-binding protein with a photoactivatable crosslinking agent capable of reacting with DNA nucleotides when exposed to UV. This method provides information on the interaction between the DNA and protein in the crosslink. DNA repair pathways can result in the formation of tumor cells. Cancer treatments have been

title: Nuclear DNA

text: the bases are held together by hydrogen bonds. Nuclear DNA and mitochondrial DNA differ in many ways, starting with location and structure. Nuclear DNA is located within the nucleus of eukaryote cells and usually has two copies per cell while mitochondrial DNA is located in the mitochondria and contains 100-1,000 copies per cell. The structure of nuclear DNA chromosomes is linear with open ends and includes 46 chromosomes containing 3 billion nucleotides. Mitochondrial DNA chromosomes usually have closed, circular structures, and contain for example 16,569 nucleotides in human. Nuclear DNA is diploid, ordinarily inheriting the DNA from two parents, while

title: DNA

text: according to the nucleotide they have read. DNA was first isolated by the Swiss physician Friedrich Miescher who, in 1869, discovered a microscopic substance in the pus of discarded surgical bandages. As it resided in the nuclei of cells, he called it "nuclein". In 1878, Albrecht Kossel isolated the non-protein component of "nuclein", nucleic acid, and later isolated its five primary nucleobases. In 1909, Phoebus Levene identified the base, sugar, and phosphate nucleotide unit of the RNA (then named "yeast nucleic acid"). In 1929, Levene identified deoxyribose sugar in "thymus nucleic acid" (DNA). Levene suggested that DNA consisted of a

title: Poverty Discovered

text: estate of James Beached at public auction. The Poverty Discovered plantation house was built c. 1760. It is log construction with brick and stone construction additions with left-centered doors. Outbuildings include a log framed structure. In the 1930s a porch was enclosed for a kitchen. William J Bryson owned the house in the 1970s and substantial renovations occurred in 1989. The building is registered by the county as HO-117, with an abbreviated history. In 1966, the Rouse Company added "Poverty Discovered" to the list of local historical names to call their new land development project. The Property is now run

title: Crosslinking of DNA

text: chemical and physical agents, including transition metals, ionizing radiation, and endogenous aldehydes, in addition to chemotherapeutic agents. Similar to DNA crosslinking, DNA-protein crosslinks are lesions in cells that are frequently damaged by UV radiation. The UV’s effect can lead to reactive interactions and cause DNA and the proteins that are in contact with it to crosslink. These crosslinks are very bulky and complex lesions. They primarily occur in areas of the chromosomes that are undergoing DNA replication and interfere with cellular processes. The advancement in structure-identification methods has progressed, and the addition in the ability to measure interactions between DNA

title: Non-coding DNA

text: amount of coding DNA, rather, it is due to a difference in the amount of non-coding DNA. In 2013, a new "record" for the most efficient eukaryotic genome was discovered with "Utricularia gibba", a bladderwort plant that has only 3% noncoding DNA and 97% of coding DNA. Parts of the noncoding DNA were being deleted by the plant and this suggested that noncoding DNA may not be as critical for plants, even though noncoding DNA is useful for humans. Other studies on plants have discovered crucial functions in portions of noncoding DNA that were previously thought to be negligible and

title: Z-DNA

text: in relation to each other as they exchange electrons, while tagged onto a DNA molecule. The distances between the fluorophores could be used to quantitatively calculate the changes in proximity of the dyes and conformational changes in the DNA. A Z-DNA high affinity binding protein, hZαADAR1, was used at varying concentrations to induce the transformation from B-DNA to Z-DNA. The smFRET assays revealed a B* transition state, which formed as the binding of hZαADAR1 accumulated on the B-DNA structure and stabilized it. This step occurs to avoid high junction energy, in which the B-DNA structure is allowed to undergo a

title: DNA-binding domain

text: minor groove of DNA, or at the sugar-phosphate DNA backbone (see the structure of DNA). Each specific type of DNA recognition is tailored to the protein's function. For example, the DNA-cutting enzyme DNAse I cuts DNA almost randomly and so must bind to DNA in a non-sequence-specific manner. But, even so, DNAse I recognizes a certain 3-D DNA structure, yielding a somewhat specific DNA cleavage pattern that can be useful for studying DNA recognition by a technique called DNA footprinting. Many DNA-binding domains must recognize specific DNA sequences, such as DBDs of transcription factors that activate specific genes, or those

title: DNA

text: by how the DNA is packaged in chromosomes, in a structure called chromatin. Base modifications can be involved in packaging, with regions that have low or no gene expression usually containing high levels of methylation of cytosine bases. DNA packaging and its influence on gene expression can also occur by covalent modifications of the histone protein core around which DNA is wrapped in the chromatin structure or else by remodeling carried out by chromatin remodeling complexes (see Chromatin remodeling). There is, further, crosstalk between DNA methylation and histone modification, so they can coordinately affect chromatin and gene expression. For one

title: DNA nanotechnology

text: being pumped out and apoptosis of the cancer cells was achieved.The tetrahedron without DOX was loaded into cells to test its biocompatibility, and the structure showed no cytotoxicity itself. Applications for DNA nanotechnology in nanomedicine also focus on mimicking the structure and function of naturally occurring membrane proteins with designed DNA nanostructures. In 2012, Langecker "et al." introduced a pore-shaped DNA origami structure that can self-insert into lipid membranes via hydrophobic cholesterol modifications and induce ionic currents across the membrane. This first demonstration of a synthetic DNA ion channel was followed by a variety of pore-inducing designs ranging from a

title: DNA polymerase

text: at which it can add the first nucleotide. Primers consist of RNA or DNA bases (or both). In DNA replication, the first two bases are always RNA, and are synthesized by another enzyme called primase. Helicase and topoisomerase II are required to unwind DNA from a double-strand structure to a single-strand structure to facilitate replication of each strand consistent with the semiconservative model of DNA replication. It is important to note that the directionality of the newly forming strand (the daughter strand) is opposite to the direction in which DNA polymerase moves along the template strand. Since DNA polymerase requires

title: DNA

text: the central set of four bases coming from either a single strand folded around the bases, or several different parallel strands, each contributing one base to the central structure. In addition to these stacked structures, telomeres also form large loop structures called telomere loops, or T-loops. Here, the single-stranded DNA curls around in a long circle stabilized by telomere-binding proteins. At the very end of the T-loop, the single-stranded telomere DNA is held onto a region of double-stranded DNA by the telomere strand disrupting the double-helical DNA and base pairing to one of the two strands. This triple-stranded structure is

title: Solenoid (DNA)

text: it is small enough to fit into the nucleus. This is a big task as the nucleus of a mammalian cell has a diameter of approximately 6 µm, whilst the DNA in one human cell would stretch to just over 2 metres long if it were unwound. The "beads on a string" structure can compact DNA to 7 times smaller. The solenoid structure can increase this to be 40 times smaller. When DNA is compacted into the solenoid structure it is not transcriptionally active. It is the secondary chromatin structure that is important for this transcriptional repression as "in vivo"

title: Z-DNA

text: conformational change to the Z-DNA structure without a major, disruptive change in energy. This result coincides with the computational results of Lee et. al. proving the mechanism to be step-wise and its purpose being that it provides a lower energy barrier for the conformational change from the B-DNA to Z-DNA configuration. Contrary to the previous notion, the binding proteins do not actually stabilize the Z-DNA conformation after it is formed, but instead they actually promote the formation of the Z-DNA directly from the B* conformation, which is formed by the B-DNA structure being bound by high affinity proteins. While it

title: DNA machine

text: key advantage in the construction of DNA machines. An example of a DNA machine was reported by Bernard Yurke and co-workers at Lucent Technologies in the year 2000, who constructed molecular tweezers out of DNA. The DNA tweezers contain three strands: A, B and C. Strand A latches onto half of strand B and half of strand C, and so it joins them all together. Strand A acts as a hinge so that the two "arms" — AB and AC — can move. The structure floats with its arms open wide. They can be pulled shut by adding a fourth

title: Biomolecular structure

text: of Bessel functions and DNA molecular models, is still routinely used to analyze A-DNA and Z-DNA X-ray diffraction patterns. Biomolecular structure prediction is the prediction of the three-dimensional structure of a protein from its amino acid sequence, or of a nucleic acid from its nucleobase (base) sequence. In other words, it is the prediction of secondary and tertiary structure from its primary structure. Structure prediction is the inverse of biomolecular design, as in rational design, protein design, nucleic acid design, and biomolecular engineering. Protein structure prediction is one of the most important goals pursued by bioinformatics and theoretical chemistry. Protein

title: Satellite DNA

text: of alternating purines and pyrimidines shown to adopt a left-handed Z-DNA helical structure in equilibrium with a stem-loop structure under superhelical stress. A fragment containing the domain was excised and subcloned in order to examine structural properties of the alternating purine and pyrimidine motif independently of the four compositionally-biased repetitive divergent domains within RU. The palindromic sequence CGCACGTGCG:CGCACGTGCG, flanked by extended palindromic Z-DNA sequences over a 35 bp domain, adopted a Z-DNA structure with a symmetrical arrangement in equilibrium with a stem-loop structure centered on the palindrome containing the CGCAC:GTGCG motif. In all RU variants examined, tandem repeats of the

title: Z-DNA

text: an A-RNA double helix into a left-handed helix. The transition from A-RNA to Z-RNA, however, was already described in 1984. Z-DNA is quite different from the right-handed forms. In fact, Z-DNA is often compared against B-DNA in order to illustrate the major differences. The Z-DNA helix is left-handed and has a structure that repeats every other base pair. The major and minor grooves, unlike A- and B-DNA, show little difference in width. Formation of this structure is generally unfavourable, although certain conditions can promote it; such as alternating purine–pyrimidine sequence (especially poly(dGC)), negative DNA supercoiling or high salt and some

title: DNA repair

text: regular helical structure by introducing non-native chemical bonds or bulky adducts that do not fit in the standard double helix. Unlike proteins and RNA, DNA usually lacks tertiary structure and therefore damage or disturbance does not occur at that level. DNA is, however, supercoiled and wound around "packaging" proteins called histones (in eukaryotes), and both superstructures are vulnerable to the effects of DNA damage. DNA damage can be subdivided into two main types: The replication of damaged DNA before cell division can lead to the incorporation of wrong bases opposite damaged ones. Daughter cells that inherit these wrong bases carry

title: DNA damage theory of aging

text: phenotype. DNA damage theory of aging The DNA damage theory of aging proposes that aging is a consequence of unrepaired accumulation of naturally occurring DNA damages. Damage in this context is a DNA alteration that has an abnormal structure. Although both mitochondrial and nuclear DNA damage can contribute to aging, nuclear DNA is the main subject of this analysis. Nuclear DNA damage can contribute to aging either indirectly (by increasing apoptosis or cellular senescence) or directly (by increasing cell dysfunction). Several review articles have shown that deficient DNA repair, allowing greater accumulation of DNA damages, causes premature aging; and that

title: DNA damage theory of aging

text: DNA damage theory of aging The DNA damage theory of aging proposes that aging is a consequence of unrepaired accumulation of naturally occurring DNA damages. Damage in this context is a DNA alteration that has an abnormal structure. Although both mitochondrial and nuclear DNA damage can contribute to aging, nuclear DNA is the main subject of this analysis. Nuclear DNA damage can contribute to aging either indirectly (by increasing apoptosis or cellular senescence) or directly (by increasing cell dysfunction). Several review articles have shown that deficient DNA repair, allowing greater accumulation of DNA damages, causes premature aging; and that increased

title: DNA glycosylase

text: of UDG is to remove mutations in DNA, more specifically removing uracil. These proteins have a 3-layer alpha/beta/alpha structure. The polypeptide topology of UDG is that of a classic alpha/beta protein. The structure consists primarily of a central, four-stranded, all parallel beta sheet surrounded on either side by a total of eight alpha helices and is termed a parallel doubly wound beta sheet. Uracil-DNA glycosylases are DNA repair enzymes that excise uracil residues from DNA by cleaving the N-glycosydic bond, initiating the base excision repair pathway. Uracil in DNA can arise either through the deamination of cytosine to form mutagenic

title: Molecular models of DNA

text: in ice is on the millisecond time scale. The proton exchange rates in DNA and attached proteins may vary from picosecond to nanosecond, minutes or years, depending on the exact locations of the exchanged protons in the large biopolymers. A simple harmonic oscillator 'vibration' is only an oversimplified dynamic representation of the longitudinal vibrations of the DNA intertwined helices which were found to be anharmonic rather than harmonic as often assumed in quantum dynamic simulations of DNA. The structure of DNA shows a variety of forms, both double-stranded and single-stranded. The mechanical properties of DNA, which are directly related to

title: I-motif DNA

text: of 0.2 ppm. I-motif DNA i-motif DNA is a type of deoxyribonucleic acid, discovered in 2018, that is found in the nuclei of human cells. An abbreviation of intercalated motif, the four-strand i-motif is unlike the iconic double helix DNA. I-motifs are four-stranded quadruplex structures formed by cytosine-rich DNA, similar to the G-quadruplex structures that guanine-rich DNA forms. C-rich DNA regions are common in gene regulation portions of the genome. Recently, i-motifs were discovered in human cells and were shown to play a role in cell reproduction. I-motifs have potential applications in nanotechnology and nanomedicine due to their unique pH

title: I-motif DNA

text: I-motif DNA i-motif DNA is a type of deoxyribonucleic acid, discovered in 2018, that is found in the nuclei of human cells. An abbreviation of intercalated motif, the four-strand i-motif is unlike the iconic double helix DNA. I-motifs are four-stranded quadruplex structures formed by cytosine-rich DNA, similar to the G-quadruplex structures that guanine-rich DNA forms. C-rich DNA regions are common in gene regulation portions of the genome. Recently, i-motifs were discovered in human cells and were shown to play a role in cell reproduction. I-motifs have potential applications in nanotechnology and nanomedicine due to their unique pH sensitivity and have

title: DNA replication

text: of the bubble, forming a replication fork with two prongs. In bacteria, which have a single origin of replication on their circular chromosome, this process creates a "theta structure" (resembling the Greek letter theta: θ). In contrast, eukaryotes have longer linear chromosomes and initiate replication at multiple origins within these. The replication fork is a structure that forms within the nucleus during DNA replication. It is created by helicases, which break the hydrogen bonds holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA. These two strands

title: Solenoid (DNA)

text: their model of the structure. This was the first model to be proposed for the structure of the 30 nm fibre. DNA in the nucleus is wrapped around nucleosomes, which are histone octamers formed of core histone proteins; two histone H2A-H2B dimers, two histone H3 proteins, and two histone H4 proteins. The primary chromatin structure, the least packed form, is the 11 nm, or “beads on a string” form, where DNA is wrapped around nucleosomes at relatively regular intervals, as Roger Kornberg proposed. Histone H1 protein binds to the site where DNA enters and exits the nucleosome, wrapping 147 base

title: Nucleic acid structure

text: units in the ribosome or spliceosome. Nucleic acid structure Nucleic acid structure refers to the structure of nucleic acids such as DNA and RNA. Chemically speaking, DNA and RNA are very similar. Nucleic acid structure is often divided into four different levels: primary, secondary, tertiary and quaternary. Primary structure consists of a linear sequence of nucleotides that are linked together by phosphodiester bonds. It is this linear sequence of nucleotides that make up the Primary structure of DNA or RNA. Nucleotides consist of 3 components: The nitrogen bases adenine and guanine are purine in structure and form a glycosidic bond

title: Nucleic acid structure

text: Nucleic acid structure Nucleic acid structure refers to the structure of nucleic acids such as DNA and RNA. Chemically speaking, DNA and RNA are very similar. Nucleic acid structure is often divided into four different levels: primary, secondary, tertiary and quaternary. Primary structure consists of a linear sequence of nucleotides that are linked together by phosphodiester bonds. It is this linear sequence of nucleotides that make up the Primary structure of DNA or RNA. Nucleotides consist of 3 components: The nitrogen bases adenine and guanine are purine in structure and form a glycosidic bond between their 9 nitrogen and the

title: DNA

text: related to the child. Normal DNA sequencing methods happen after birth, but there are new methods to test paternity while a mother is still pregnant. Deoxyribozymes, also called DNAzymes or catalytic DNA, are first discovered in 1994. They are mostly single stranded DNA sequences isolated from a large pool of random DNA sequences through a combinatorial approach called in vitro selection or systematic evolution of ligands by exponential enrichment (SELEX). DNAzymes catalyze variety of chemical reactions including RNA-DNA cleavage, RNA-DNA ligation, amino acids phosphorylation-dephosphorylation, carbon-carbon bond formation, and etc. DNAzymes can enhance catalytic rate of chemical reactions up to 100,000,000,000-fold

title: Molecular models of DNA

text: is carried by spool-like proteins named histones, around which DNA winds. It is the further compaction of this DNA-protein complex which produces the well known mitotic eukaryotic chromosomes. In the late 1970s, alternate non-helical models of DNA structure were briefly considered as a potential solution to problems in DNA replication in plasmids and chromatin. However, the models were set aside in favor of the double-helical model due to subsequent experimental advances such as X-ray crystallography of DNA duplexes, and later the nucleosome core particle, and the discovery of topoisomerases. Such non-double-helical models are not currently accepted by the mainstream scientific

title: DNA

text: grow, but, when a cell divides, it must replicate the DNA in its genome so that the two daughter cells have the same genetic information as their parent. The double-stranded structure of DNA provides a simple mechanism for DNA replication. Here, the two strands are separated and then each strand's complementary DNA sequence is recreated by an enzyme called DNA polymerase. This enzyme makes the complementary strand by finding the correct base through complementary base pairing and bonding it onto the original strand. As DNA polymerases can only extend a DNA strand in a 5′ to 3′ direction, different mechanisms

title: DNA damage (naturally occurring)

text: DNA damage (naturally occurring) DNA damage is distinctly different from mutation, although both are types of error in DNA. DNA damage is an abnormal chemical structure in DNA, while a mutation is a change in the sequence of standard base pairs. DNA damages cause changes in the structure of the genetic material and prevents the replication mechanism from functioning and performing properly. DNA damage and mutation have different biological consequences. While most DNA damages can undergo DNA repair, such repair is not 100% efficient. Un-repaired DNA damages accumulate in non-replicating cells, such as cells in the brains or muscles of

title: DNA polymerase

text: DNA replication process by which DNA polymerase copies the base sequence of a template DNA strand. Kornberg was later awarded the Nobel Prize in Physiology or Medicine in 1959 for this work. DNA polymerase II was also discovered by Thomas Kornberg (the son of Arthur Kornberg) and Malcolm E. Gefter in 1970 while further elucidating the role of Pol I in "E. coli" DNA replication. The main function of DNA polymerase is to synthesize DNA from deoxyribonucleotides, the building blocks of DNA. The DNA copies are created by the pairing of nucleotides to bases present on each strand of the

title: DNA

text: template as part of its structure. It synthesizes telomeres at the ends of chromosomes. Telomeres prevent fusion of the ends of neighboring chromosomes and protect chromosome ends from damage. Transcription is carried out by a DNA-dependent RNA polymerase that copies the sequence of a DNA strand into RNA. To begin transcribing a gene, the RNA polymerase binds to a sequence of DNA called a promoter and separates the DNA strands. It then copies the gene sequence into a messenger RNA transcript until it reaches a region of DNA called the terminator, where it halts and detaches from the DNA. As

title: DNA profiling

text: samples are degraded samples and DNA mixtures. In the real world DNA labs often have to deal with DNA samples that are less than ideal. DNA samples taken from crime scenes are often degraded, which means that the DNA has started to break down into smaller fragments . Victims of homicides might not be discovered right away, and in the case of a mass casualty event it could be hard to get DNA samples before the DNA has been exposed to degradation elements. Degradation or fragmentation of DNA at crime scenes can occur because of a number of reasons, with

title: Molecular models of DNA

text: double helix. Animated molecular models, such as the wire, or skeletal, type shown at the top of this article, allow one to visually explore the three-dimensional (3D) structure of DNA. Another type of DNA model is the space-filling, or CPK, model. The hydrogen bonding dynamics and proton exchange is very different by many orders of magnitude between the two systems of fully hydrated DNA and water molecules in ice. Thus, the DNA dynamics is complex, involving nanosecond and several tens of picosecond time scales, whereas that of liquid ice is on the picosecond time scale, and that of proton exchange

title: DNA

text: double-stranded sequence of a DNA helix is duplicated on each strand, which is vital in DNA replication. This reversible and specific interaction between complementary base pairs is critical for all the functions of DNA in living organisms. The two types of base pairs form different numbers of hydrogen bonds, AT forming two hydrogen bonds, and GC forming three hydrogen bonds (see figures, right). DNA with high GC-content is more stable than DNA with low GC-content. As noted above, most DNA molecules are actually two polymer strands, bound together in a helical fashion by noncovalent bonds; this double-stranded (dsDNA) structure is

title: I-motif DNA

text: Zeraati at Garven says the i-motif was dicovered for its appearing and disappearing within the cell and distinctive connections via cytosines rather than letters. The research team developed a precise new tool to find the i-motif – a fragment of an antibody molecule – that could specifically recognise and attach to i-motifs "with a very high affinity". G-quadruplex DNA structures exist in G-rich areas of DNA. The complementary cytosine-rich DNA strand can also form a four-stranded quadruplex structure called i-motif. The cytosine base pairs in the i-motif structure form an intercalated and anti-parallel tetramer structure. This structure is formed through

title: Nucleic acid quaternary structure

text: Nucleic acid quaternary structure Nucleic acid quaternary structure refers to the interactions between separate nucleic acid molecules, or between nucleic acid molecules and proteins. The concept is analogous to protein quaternary structure, but as the analogy is not perfect, the term is used to refer to a number of different concepts in nucleic acids and is less commonly encountered. DNA quaternary structure is used to refer to the binding of DNA to histones to form nucleosomes, and then their organisation into higher-order chromatin fibres. The quaternary structure of DNA strongly affects how accessible the DNA sequence is to the transcription

title: Molecular models of DNA

text: types, attached to deoxyribose and phosphate groups), its molecular structure "in vivo" undergoes dynamic configuration changes that involve dynamically attached water molecules and ions. Supercoiling, packing with histones in chromosome structures, and other such supramolecular aspects also involve "in vivo" DNA topology which is even more complex than DNA molecular geometry, thus turning molecular modeling of DNA into an especially challenging problem for both molecular biologists and biotechnologists. Like other large molecules and biopolymers, DNA often exists in multiple stable geometries (that is, it exhibits conformational isomerism) and configurational, quantum states which are close to each other in energy on

title: DNA replication

text: by unwinding the two strands of the DNA helix; topoisomerases (including DNA gyrase) achieve this by adding negative supercoils to the DNA helix. Bare single-stranded DNA tends to fold back on itself forming secondary structures; these structures can interfere with the movement of DNA polymerase. To prevent this, single-strand binding proteins bind to the DNA until a second strand is synthesized, preventing secondary structure formation. Clamp proteins form a sliding clamp around DNA, helping the DNA polymerase maintain contact with its template, thereby assisting with processivity. The inner face of the clamp enables DNA to be threaded through it. Once

title: Nuclear DNA

text: Nuclear DNA Nuclear DNA (nDNA), or nuclear deoxyribonucleic acid, is the DNA contained within each cell nucleus of a eukaryotic organism. Nuclear DNA encodes for the majority of the genome in eukaryotes, with mitochondrial DNA and plastid DNA coding for the rest. Nuclear DNA adheres to Mendelian inheritance, with information coming from two parents, one male and one female, rather than matrilineally (through the mother) as in mitochondrial DNA. Nuclear DNA is a nucleic acid, a polymeric biomolecule or biopolymer, found in the nucleus of eukaryotic organisms. Its structure is a double helix, with two strands wound around each other.

title: DNA

text: molecular tool to explore physical laws and theories, such as the ergodic theorem and the theory of elasticity. The unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro- and nano-fabrication. Among notable advances in this field are DNA origami and DNA-based hybrid materials. 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.

title: DNA-binding protein

text: such domains as the zinc finger, the helix-turn-helix, and the leucine zipper (among many others) that facilitate binding to nucleic acid. There are also more unusual examples such as transcription activator like effectors. Structural proteins that bind DNA are well-understood examples of non-specific DNA-protein interactions. Within chromosomes, DNA is held in complexes with structural proteins. These proteins organize the DNA into a compact structure called chromatin. In eukaryotes, this structure involves DNA binding to a complex of small basic proteins called histones. In prokaryotes, multiple types of proteins are involved. The histones form a disk-shaped complex called a nucleosome, which

title: A-DNA

text: and shallow. A-DNA is broader and apparently more compressed along its axis than B-DNA. Dehydration of DNA drives it into the A form, and this apparently protects DNA under conditions such as the extreme desiccation of bacteria. Protein binding can also strip solvent off of DNA and convert it to the A form, as revealed by the structure of a rod-shaped virus. It has been proposed that the motors that package double-stranded DNA in bacteriophages exploit the fact that A-DNA is shorter than B-DNA, and that conformational changes in the DNA itself are the source of the large forces generated

title: Poverty Discovered

text: Poverty Discovered Located Cooksville in Howard County, Maryland, United States, Poverty Discovered, "Summer Hill Farm" "Poverty Discovered" is named after the 1737 acre land tract Given to Joseph Hobbs by Lord Calvert in 1760. It was then owned by Captain Thomas Hobbs, who was involved in the burning of the Peggy Stwewart. He willed the property to his son, Kentucky General Assemblyman Joseph Hobbs Jr. The slave farm was situated on the road to Ellicott's Mills from Hood's Mill. By 1783, "Poverty Discovered" was subdivided and consisted of 400 acres. In November 3, 1793 Henry Howard sold the Poverty Discovered

title: DNA replication

text: strands by adding nucleotides that complement each (template) strand. DNA replication occurs during the S-stage of interphase. DNA replication (DNA amplification) can also be performed "in vitro" (artificially, outside a cell). DNA polymerases isolated from cells and artificial DNA primers can be used to initiate DNA synthesis at known sequences in a template DNA molecule. Polymerase chain reaction (PCR), ligase chain reaction (LCR), and transcription-mediated amplification (TMA) are examples. DNA exists as a double-stranded structure, with both strands coiled together to form the characteristic double-helix. Each single strand of DNA is a chain of four types of nucleotides. Nucleotides in