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Strings of nucleotides are bonded to form spiraling backbones and assembled into chains of bases or base-pairs selected from the five primary, or canonical, nucleobases. RNA usually forms a chain of single bases, whereas DNA forms a chain of base pairs. The bases found in RNA and DNA are: adenine, cytosine, guanine, thymine, and uracil. Thymine ...
DNA and RNA also contain other (non-primary) bases that have been modified after the nucleic acid chain has been formed. In DNA, the most common modified base is 5-methylcytosine (m 5 C). In RNA, there are many modified bases, including those contained in the nucleosides pseudouridine (Ψ), dihydrouridine (D), inosine (I), and 7-methylguanosine ...
A section of DNA. The bases lie horizontally between the two spiraling strands [15] (animated version). The DNA double helix is stabilized primarily by two forces: hydrogen bonds between nucleotides and base-stacking interactions among aromatic nucleobases. [16] The four bases found in DNA are adenine (A), cytosine (C), guanine (G) and thymine (T).
In an aqueous solution, the average persistence length has been found to be of around 50 nm (or 150 base pairs). [43] More broadly, it has been observed to be between 45 and 60 nm [44] or 132–176 base pairs (the diameter of DNA is 2 nm) [45] This can vary significantly due to variations in temperature, aqueous solution conditions and DNA ...
The nucleobases are important in base pairing of strands to form higher-level secondary and tertiary structures such as the famed double helix. The possible letters are A , C , G , and T , representing the four nucleotide bases of a DNA strand – adenine , cytosine , guanine , thymine – covalently linked to a phosphodiester backbone.
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. [2]
The degree of unwinding varies depending on the intercalator; for example, ethidium cation (the ionic form of ethidium bromide found in aqueous solution) unwinds DNA by about 26°, whereas proflavine unwinds it by about 17°. This unwinding causes the base pairs to separate, or "rise", creating an opening of about 0.34 nm (3.4 Å).
Ten years after James Watson and Francis Crick published their model of the DNA double helix, [2] Karst Hoogsteen reported [3] a crystal structure of a complex in which analogues of A and T formed a base pair that had a different geometry from that described by Watson and Crick. Similarly, an alternative base-pairing geometry can occur for G ...