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Diamond and graphite are two allotropes of carbon: pure forms of the same element that differ in crystalline structure.. Allotropy or allotropism (from Ancient Greek ἄλλος (allos) 'other' and τρόπος (tropos) 'manner, form') is the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of the elements.
Under torsional stress, a Z-DNA structure can form with opposite twist to B-form DNA, but this is rare within the cellular environment. [24] The discovery of topoisomerases and gyrases , enzymes that can change the linking number of circular nucleic acids and thus "unwind" and "rewind" the replicating bacterial chromosome, solved the ...
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, which subsequently turned out to be incorrect. [3] Both Crick, and particularly Watson, thought that they were racing against Pauling to discover the structure of DNA.
The DNA model shown (far right) is a space-filling, or CPK, model of the DNA 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 DNA structure at left (schematic shown) will self-assemble into the structure visualized by atomic force microscopy at right. DNA nanotechnology is the field that seeks to design nanoscale structures using the molecular recognition properties of DNA molecules.
The double-helix model of DNA structure was first published in the journal Nature by James Watson and Francis Crick in 1953, [6] (X,Y,Z coordinates in 1954 [7]) based on the work of Rosalind Franklin and her student Raymond Gosling, who took the crucial X-ray diffraction image of DNA labeled as "Photo 51", [8] [9] and Maurice Wilkins, Alexander Stokes, and Herbert Wilson, [10] and base-pairing ...
DNA is a macromolecule made up of nucleotide units, which are linked by covalent bonds and hydrogen bonds, in a repeating structure. DNA synthesis occurs when these nucleotide units are joined to form DNA; this can occur artificially (in vitro) or naturally (in vivo). Nucleotide units are made up of a nitrogenous base (cytosine, guanine ...
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.