In biochemistry, the linkage of two base (purine or pyrimidine) molecules that join the complementary strands of
DNA. Adenine forms a base pair with thymine (or uracil in
RNA) and cytosine pairs with guanine in a double-stranded
nucleic acid molecule.
One base lies on one strand of the DNA double helix and one on the other, so that the base pairs link the two strands like the rungs of a ladder. In DNA, there are four bases: adenine and guanine (purines) and cytosine and thymine (pyrimidines). Adenine always pairs with thymine and cytosine with guanine.
The sizes of genes and genomes are commonly cited in base pairs, for example the human genome consists of around 3 billion base pairs.
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