11. Which of the following statements is correct regarding the biosynthesis of purine nucleotides? (A) Glycine, aspartate, and glutamine serve as nitrogen sources for the purine ring. (B) The concentration of 5-phosphoribosyl 1-pyrophosphate is the major factor regulating the rate of de novo purine nucleotide biosynthesis. (C) Lesch-Nyhan syndrome is caused by a defect in hypoxanthine-guanine phosphoribosyl transferase, an enzyme involved in purine salvage. (D) AMP and GMP inhibit hypoxanthine-guanine phosphoribosyl transferase, which converts hypoxanthine and guanine into IMP and GMP. (E) All of the above are correct.