base pair

2 nucleotides in DNA or RNA paired by hydrogen bonds. The common bairs pairs are purine-pyrimidine pairs, including: adenine - thymine or A - T (DNA) adenine - uracil or A - U (RNA) guanine - cytosine or G - C (DNA, RNA) It is the selectivity of these base pairs that allows sequences of them to store biological information in DNA & be transcribed in the form of RNA.

References

Alperts et al Molecular Biology of the Cell, Garland Publishing, New York, NY 1989