What key molecule exits the cycle and feeds into the electron transport chain?

The key molecules that exit the citric acid cycle and feed into the electron transport chain are NADH and FADH2. During the citric acid cycle, several reactions occur that result in the reduction of NAD+ to NADH and FAD to FADH2. These reduced cofactors play a crucial role in cellular respiration, as they carry high-energy electrons to the electron transport chain located in the inner mitochondrial membrane.

NADH and FADH2 donate their electrons to complex I and complex II of the electron transport chain, respectively. This transfer of electrons is essential for the generation of a proton gradient across the mitochondrial membrane, which ultimately drives the synthesis of ATP through oxidative phosphorylation. Therefore, NADH and FADH2 are not only products of the citric acid cycle but also vital for energy production in the form of ATP through their involvement in the electron transport chain.