Biochemistry) A nitrogenous molecule, either a PYRIMIDINE or a PURINE, that combines with a pentose sugar and phosphoric acid to form a nucleotide, the fundamental unit of nucleic acids.

• 2碱基：一种含氮的分子，嘌呤碱或者是嘧啶碱，它们和戊糖还有磷酸一起构成核苷酸，核苷酸是核酸的基本结构单位。