In molecular biology, two nucleotides on opposite complementary DNA or RNA strands that're connected via hydrogen bonds are called a base pair (often abbreviated bp). In the canonical Watson-Crick base pairing, adenine (A) forms a base pair with thymine (T), as does guanine (G) with cytosine (C) in DNA. In RNA, thymine's replaced by uracil (U). Non-Watson-Crick base pairing with alternate hydrogen bonding patterns also occur, especially in RNA; common such patterns are Hoogsteen base pairs.Pairi… (More on Kilobase)