[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).
The purine bases have a 9âmembered doubleâring system with four nitrogens and five carbons. Although both purine and pyrimidine rings have one 6âmembered component with two nitrogens and four carbons, the purines and pyrimidnes are not related metabolically. Distinct pathways for purine biosynthesis and degradation and for pyrimidine biosynthesis and degradation, exist in all organisms.