pyrimidine A basic, 6-membered heterocyclic compound. The principal pyrimidines (uracil, thymine, and cytosine) are important constituents of nucleic acids. Thiamine (vitamin B₁) is an important pyrimidine derivative, and other derivatives play major roles in carbohydrate and lipid metabolism.

pyrimidine An organic nitrogenous base (see formula), sparingly soluble in water, that gives rise to a group of biologically important derivatives, notably uracil, thymine, and cytosine, which occur in nucleotides and nucleic acids (DNA and RNA).

pyrimidine A basic, six-membered, heterocyclic compound; the principal pyrimidines (uracil, thymine, and cytosine) are important constituents of nucleic acids. Thiamine (vitamin B₁) is an important pyrimidine derivative, and other derivatives play major roles in carbohydrate and lipid metabolism.

pyrimidine A nitrogen base composed of a single, six-membered ring structure. The pyrimidine bases in the nucleotides of nucleic acids are cytosine and thymine in DNA and cytosine and uracil in RNA.

pyrimidine (pi-rim-i-deen) n. a nitrogen-containing compound with a ring molecular structure. The commonest pyrimidines are cytosine, thymine, and uracil, which form the nucleotides of nucleic acids.