| Base Pair (bp) | Two nucleotides that are in different nucleic acid chains and whose bases pair by hydrogen bonding. In DNA, the nucleotide bases are adenine (A) that always pairs with thymine (T) and guanine (G) which pairs with cytosine (C). In RNA molecules, adenine (A) joins the uracil (U). Two strands of DNA are held together in the shape of a double helix by the bonds between these pairs. |