base pair
(bays payr)
Two nitrogen-containing bases (or nucleotides) that pair together to form the structure of DNA. The four bases in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T). These bases form specific pairs (A with T, and G with C). Base pair may also refer to the actual number of base pairs, such as 8 base pairs, in a sequence of nucleotides.
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![DNA base pair; drawing shows double-stranded DNA with bonds between two pairs of nitrogen-containing bases [adenine (A) and thymine (T), and cytosine (C) and guanine (G)].](https://nci-media.cancer.gov/pdq/media/images/686274-571.jpg)
Enlarge this image in new windowDNA base pair. Under normal circumstances, the nitrogen-containing bases adenine (A) and thymine (T) pair together, and cytosine (C) and guanine (G) pair together. The binding of these base pairs forms the structure of DNA.