Question

In the biosynthesis of nucleotides, pyrimidines are assembled starting with ribose-5-phosphate while ribose-5-phosphate is added after synthesis of the nitrogenous base for purines.

Answer 1

The biosynthesis of pyrimidine nucleotides starts with the formation of the pyrimidine ring followed by its attachment to ribose-5-phosphate, leading to uridylate (UMP), then to CMP and TMP. On the other hand, purine nucleotides are synthesized with the purine ring and ribose phosphate concurrently, resulting in nucleotides like adenylate.

Step-by-step explanation:

Biosynthesis of Nucleotides:

The biosynthesis of pyrimidine nucleotides involves the formation of a pyrimidine ring prior to its attachment to ribose-5-phosphate. Initially, carbamoyl phosphate and aspartate combine to form carbamoyl aspartate. Subsequent enzymatic reactions lead to the formation of dihydroorotate, orotic acid, and eventually orotidylic acid, which is decarboxylated to form uridylate (UMP). UMP is the precursor for other pyrimidine nucleotides such as cytidine monophosphate (CMP) and thymidine monophosphate (TMP).

In contrast, the biosynthesis of purine nucleotides is characterized by the assembly of the purine ring concurrently with its attachment to ribose-5-phosphate derived from the HMP pathway. Precursors such as aspartate, glutamine, and glycine contribute atoms to the purine ring, ultimately forming nucleotides like adenylate, which contains adenine.