In biosynthesis the base is assembled first and then attached to ribose.

In pyrimidine biosynthesis, the base is assembled first and then attached to ribose. Pyrimidine is a heterocyclic aromatic organic compound which contains two nitrogen atoms at positions 1 and 3 of the six-member ring.Pyrimidine biosynthesis is a biological process which results in the formation of a pyrimidine nucleotide. In pyrimidine biosynthesis, pyrimidines (the base) are synthesized from carbamoyl phosphate and aspartate. Ribose-5-phosphate is then attached to yield pyrimidine nucleotides. Pyrimidine biosynthesis takes place both in the body and through organic synthesis.

C. gemstones they are the only non metallic mineral from the list.