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The nucleic acid notation currently in use was first formalized by the International Union of Pure and Applied Chemistry (IUPAC) in 1970. [1] This universally accepted notation uses the Roman characters G, C, A, and T, to represent the four nucleotides commonly found in deoxyribonucleic acids (DNA).
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 ...
The A form occurs under non-physiological conditions in partly dehydrated samples of DNA, while in the cell it may be produced in hybrid pairings of DNA and RNA strands, and in enzyme-DNA complexes. [ 54 ] [ 55 ] Segments of DNA where the bases have been chemically modified by methylation may undergo a larger change in conformation and adopt ...
From this position, the ligand diffuses along the surface of the DNA and may slide into the hydrophobic environment found between two base pairs that may transiently "open" to form an intercalation site, allowing the ethidium to move away from the hydrophilic (aqueous) environment surrounding the DNA and into the intercalation site. The base ...
In one study, the characteristic C3'-endo pucker is found on the first three sugars of the DNA strand, while the last three sugars have a C2'-endo pucker, like B-DNA. [2] These intermediates can form in aqueous solutions when the cytosine bases are methylated or brominated, altering the conformation.
Calcium oxide is also a separate mineral species (with the unit formula CaO), named 'Lime'. [30] [31] It has an isometric crystal system, and can form a solid solution series with monteponite. The crystal is brittle, pyrometamorphic, and is unstable in moist air, quickly turning into portlandite (Ca(OH) 2). [32]
2,6-Di-tert-butylpyridine, a weak non-nucleophilic base [2] pK a = 3.58; Phosphazene bases, such as t-Bu-P 4 [3] Non-nucleophilic bases of high strength are usually anions. For these species, the pK a s of the conjugate acids are around 35–40. Lithium diisopropylamide (LDA), pK a = 36
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.