Most of the energy from glucose oxidation during glycolysis and the citric acid cycle is stored in the electron carriers NADH and FADH2, which are later used in oxidative phosphorylation to produce the majority of ATP.
The student asked what happened to most of the energy that the cell obtains from the oxidation of glucose since glycolysis and the citric acid cycle yield only a few molecules of ATP.
Most of the energy from the oxidation of glucose is not directly converted into ATP during these two processes. Instead, it is transferred to high-energy electron carriers, specifically NADH and FADH2.
During glycolysis, some ATP is produced while high-energy electrons are also transferred to molecules of NAD+ to produce NADH.
These molecules carry electrons to the electron transport chain for oxidative phosphorylation, where the bulk of ATP will be generated.
Within the citric acid cycle, each acetyl-CoA molecule produces 3 NADH molecules and 1 FADH2 molecule.
Hence, the two acetyl-CoA molecules derived from one glucose molecule ultimately result in 6 NADH and 2 FADH2 molecules.
The energy these carriers contain is then utilized during the final stage of cellular respiration, oxidative phosphorylation, to produce a substantial amount of ATP for the cell.