試題詳解

41. Which of the following statements is     correct     of the biosynthetic pathways for purine and pyrimidine nucleotides?

(1) The amino acid aspartate is directly involved in the purine biosynthetic pathway.

(2) 5-Phosphoribosyl-1-pyrophosphate (PRPP) is a synthetic precursor for UMP.

(3) Orotic acid is an essential precursor for purine nucleotides. 

(4) Inosinate is the precursor for the synthesis of pyrimidine nucleotides.

(5) The carbamoyl phosphate required in pyrimidine biosynthesis is made in the cytosol by carbamoyl phosphate synthetase II.
(A) 1 and 4.
(B) 1, 2, and 3.
(C) 4 and 5.
(D) 1, 2, and 5.
(E) 2 only.