[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).
To answer your question, the sides, or the backbone of the DNA is made up of alternating phosphate and deoxyribose residues. On the carbon labeled #1 on the deoxyribose sugar, you have the base added to it. These bases form the rungs of the DNA molecule. Adenine, Thymine, Cytosine and Guanine are the four possible bases. There are two different types of bases, purines and pyrimidines. They refer to the basic structure, or backbone if you will, of the bases.