Correct option is A
The statement (A) is incorrect because the biosynthesis of purine and pyrimidine nucleotides involves different processes. While both pathways start with ribose-5-phosphate, the biosynthesis of purines and pyrimidines follows different routes. In purine biosynthesis, the ribose ring is built by attaching nitrogenous bases step by step. However, in pyrimidine biosynthesis, the base is synthesized first and then attached to ribose-5-phosphate.
Important Key Points:
Purine synthesis: Begins with ribose-5-phosphate, and a purine ring is built onto it.
Pyrimidine synthesis: The pyrimidine base is built first, and then ribose-5-phosphate is added.
Statement (A) suggests both processes follow the same route, which is inaccurate.
Knowledge Booster:
Option B: The first purine nucleotide biosynthesized by the de novo pathway is inosinic acid or IMP, which is correct.
Option C: The first pyrimidine nucleotide biosynthesized by the de novo pathway is orotidilic acid (or orotidine monophosphate), which is also correct.
Option D: Thymidylate (TMP) is synthesized from deoxy-UMP by the enzyme thymidylate synthetase. so this is also correct.
