Final answer:
AMP inhibits the first step of purine synthesis to prevent excess adenine nucleotide formation, and GMP also inhibits the same step to control guanine nucleotide synthesis.
Step-by-step explanation:
AMP and GMP are nucleotides that participate in feedback inhibition of purine synthesis. During the regulated pathway, AMP inhibits the first step which is the conversion of ribose-5-phosphate to PRPP, preventing excess adenine nucleotide formation. GMP inhibits the same first step, ensuring balanced guanine nucleotide synthesis. Both act to maintain nucleotide homeostasis by avoiding overproduction, as the committed step in the pathway determines the irreversible continuation towards the final purine nucleotide product.