Final answer:
The energy cost for adding a molecule of glucose to a growing glycogen chain from a blood glucose molecule is 1 ATP and 1 UTP, as G1P is activated to UDP-glucose and then transferred to the glycogen chain.
Step-by-step explanation:
The energy cost of adding a molecule of glucose to a growing glycogen chain is 1 ATP and 1 UTP. The process starts with the glucose imported from the blood being phosphorylated to glucose-6-phosphate (G6P), which then isoforms to glucose-1-phosphate (G1P). G1P is activated to UDP-glucose at a cost of 1 UTP, followed by the transfer of the glucose moiety to the glycogen chain, with UDP produced in the process. This transfer is catalyzed by the enzyme glycogen synthase and does not require ATP directly. Nevertheless, to form UDP-glucose, UTP and glucose-1-phosphate react, which indirectly involves ATP, as UTP is energetically equivalent to ATP. Therefore, the overall process consumes 1 UTP and involves an ATP → ADP + Pi via nucleoside-diphosphate kinase, which converts an ATP to UTP.