g The ring is built onto ribose-5-phosphate of PRPP for its de-novo nucleotide biosynthesis, while the ring structure of the bases are synthesized separately and then coupled to ribose-5-phosphate via the C-N glycosidic bond.

The purine ring is built onto ribose-5-phosphate of PRPP for its de-novo nucleotide biosynthesis, while the ring structure of the pyrimidine bases are synthesized separately and then coupled to ribose-5-phosphate via the C-N glycosidic bond.

Explanation:

Purines are produced as bases attached to the ribose 5-phosphate (pentose sugar). The adenine and guanine nucleotides derive from inosine monophosphate (IMP), which is synthesized on an existing ribose-phosphate. Thus, purine bases are built on a ribose sugar that is directly attached to the pyrimidine ring. On the other hand, pyrimidines are produced from the carbamoyl phosphate precursor. In this case, the ribose-5-phosphate pentose sugar is attached after the pyrimidine ring is made.

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