Which base pairs with adenine in Watson–Crick DNA base pairing? Adenine pairs with thymine.
In DNA, adenine, abbreviated A, forms a complementary base pair with thymine, abbreviated T. The pair is held together by two hydrogen bonds and fits the regular geometry of the double helix. The other standard DNA pairing is guanine with cytosine.
This rule is a consequence of molecular shape and hydrogen-bonding patterns. Adenine is a purine, while thymine is a pyrimidine; pairing one larger base with one smaller base helps maintain a consistent width across the helix. The complementary arrangement also lets each DNA strand serve as a template during replication.
Uracil is the common mix-up. It pairs with adenine in RNA, where uracil generally takes the place of thymine. In DNA, however, thymine is the canonical partner. A–T pairs contain two hydrogen bonds, whereas G–C pairs contain three, though overall DNA stability also depends strongly on base-stacking interactions.