25. The synthesis of purine and pyrimidine nucleotides differ in that:
(A) ATP is required in the synthesis of purines but not in the synthesis of pyrimidines.
(B) purine biosynthesis starts with the formation of PRPP, whereas pyrimidines incorporate the PRPP near the end of the pathway.
(C) purine formation requires a THF derivative, whereas pyrimidine formation does not.
(D) pyrimidine biosynthesis is tightly regulated in the cell, whereas purine biosynthesis is not.
(E) pyrimidines go through many steps, adding a single carbon or nitrogen each time, whereas the basic skeleton for purines is formed by two main precursors.