XDNA

xDNA is a modified form of DNA with 8 nucleobases: the four natural bases A, C, G, and T, and four artificial modifications of these made longer by the addition of an extra benzene ring: xA, xC, xG, and xT. [cite journal | last = Lynch | first = Stephen R. | coauthors = Haibo Liu, Jianmin Gao, and Eric T. Kool | year = 2006 | month = October | title = Toward a Designed, Functioning Genetic System with Expanded-Size Base Pairs: Solution Structure of the Eight-Base xDNA Double Helix | journal = Journal of the American Chemical Society | volume = 128 | issue = 45 | pages = 14704–14711 | doi = 10.1021/ja065606n ] A pairs with xT, C pairs with xG, G pairs with xC, and T pairs with xA, so the distance between the two halves of the double helix is consistently greater. The double helix is thus wider and has a longer pitch.

Experiments with xDNA are expected to provide new insight into the behavior of natural DNA. Also, the extended bases xA, xC, xG, and xT are fluorescent, and single strands composed of only extended bases can recognize and bind to single strands of natural DNA, which could make them useful tools for studying biological systems. The same research group also constructed widened DNA, called yDNA.

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