Which component of the Citric Acid Cycle directly contributes electrons to the electron transport chain?

In the Citric Acid Cycle, both NADH and FADH2 serve as crucial electron carriers that directly contribute electrons to the electron transport chain. During the cycle, NAD+ is reduced to NADH at multiple steps, specifically during the conversion of isocitrate to α-ketoglutarate and during the conversion of malate to oxaloacetate. Similarly, FAD is reduced to FADH2 when succinate is converted to fumarate.

Once produced, NADH and FADH2 are then utilized in the electron transport chain, where they donate electrons, leading to the generation of ATP through oxidative phosphorylation. The NADH contributes more energy than FADH2 because it enters the electron transport chain at a higher energy level, thus producing more ATP per molecule.

Succinyl-CoA, on the other hand, does not directly contribute electrons; it plays a different role in the cycle, participating in the conversion to succinate, which ultimately leads to the production of FADH2. Hence, the answer identifies the correct components essential for the electron transport process, affirming the integral role both NADH and FADH2 play.