[too rz duh fawrs, -fohrs; French toor duh fawrs] /ËtÊÉrz dÉ ËfÉrs, -ËfoÊrs; French tur dÉ ËfÉrs/ (Show IPA) 1. an exceptional achievement by an artist, author, or the like, that is unlikely to be equaled by that person or anyone else; stroke of genius: Herman Melville's Moby Dick was a tour de force. 2. a particularly adroit maneuver or technique in handling a difficult situation:
edit Nucleobases. Purines make up two of the four nucleobases in DNA and RNA: adenine and guanine. Pyramidines make up the other bases in DNA and RNA: cytosine, thymine (in DNA) and uracil (in RNA).
There are two kinds of nitrogen-containing bases-purines and pyrimidines. Purines consist of a six-membered and a five-membered nitrogen-containing ring, fused together. Pyridmidines have only a six-membered nitrogen-containing ring.denine and guanine are found in both DNA and RNA. Hypoxanthine and xanthine are not incorporated into the nucleic acids as they are being synthesized but are important intermediates in the synthesis and degradation of the purine nucleotides.