Base pair

Two bases which form a “rung of the DNA ladder”. A DNA nucleotide is made of a molecule of sugar, a molecule of phosphoric acid, and a molecule called a base. The bases are the “letters” that spell out the genetic code. In DNA, the code letters are A, T, C, and G, which stand respectively for the chemicals adenine, thymine, cytosine, and guanine. In base pairing, adenine always pairs with thymine, and guanine, with cytosine.