Question

Which of the following is true of the metabolism of purine and pyrimidine nucleotides?

	A.	Pyrimidine nucleotide biosynthesis is tightly regulated in the cell, whereas purine nucleotide biosynthesis is not.
	B.	These metabolic pathways occur only in humans, but not in plants and bacteria
	C.	Degradation of GTP to uric acid would require the use of (at least) a nucleotidase, a nucleosidase, and xanthine oxidase
	D.	Purine nucleotide degradation leads to the formation of ammonia and H2O, whereas pyrimidine nucleotide degradation leads to the formation of allopurinol
	E.	Energy input is required for the synthesis of purine nucleotides but not for the synthesis of pyrimidine nucleotides.

Answer 1

Answer- C. Degradation of GTP to uric acid would require the use of (at least) a nucleotidase, a nucleosidase, and xanthine oxidase

Explanation- during degradation of GTP, 5'- nucleotidase require that converts GMP into guanosine, then nucleosidase converts guanosine to guanine, then guanine deaminase converts guanine into xanthine and in last step xanthine oxidase converts xanthine into uric acid.

False statements are-

A. Pyrimidine nucleotide biosynthesis is tightly regulated in the cell, whereas purine nucleotide biosynthesis is not- purine nucleotide biosynthesis is tightly regulated at several steps by feedback mechanisms by AMP, GMP and ADP and pyrimidine nucleotide biosynthesis is tightly regulated by feedback mechanism by CTP. So that purine and pyrimidine nucleotide biosynthesis both are regulated tightly.

B. These metabolic pathways occur only in humans, but not in plants and bacteria- purines and pyrimidines are required for DNA and RNA synthesis, so that these metabolic pathways occurs in all organisms including humans, plants, bacteria etc.

D. Purine nucleotide degradation leads to the formation of ammonia and H2O, whereas pyrimidine nucleotide degradation leads to the formation of allopurinol - purine nucleotide degradation leads to the formation of NH3, H2O2, and uric acid, whereas pyrimidine nucleotide degradation leads to the formation of NH4+ and methylmalonyl -semialdehyde.

E. Energy input is required for the synthesis of purine nucleotides but not for the synthesis of pyrimidine nucleotides- purine and pyrimidine synthesis are synthetic pathways that is anabolic pathways and anabolic pathways require input of energy.