The biosynthesis of both AMP and GMP requires the hydrolysis of several high-energy bonds. To produce IMP from D-ribose 5-phosphate requires the hydrolysis of five high-energy bonds (one PPi and five ATP). To convert IMP to AMP requires the hydrolysis of one more high-energy bond (from GTP). And to convert IMP to GMP requires the hydrolysis of two high-energy bonds — one ATP and one PPi. Anaerobic organisms, such as the bacteria responsible for tetanus or botulism, must oxidize four glucose molecules at two ATP per glucose to meet the energy requirement. An aerobic organism, like you, for example, needs to oxidize only one glucose molecule at 36 or 38 ATP per glucose. The preceding processes require a substantial amount of energy. Sometimes this energy requirement may be lessened by metabolic processes known as the salvage pathways. In the salvage pathways, nitrogen bases are recycled instead of synthesized. The nitrogen bases are then converted to nucleotides.
