During which step of the Citric Acid Cycle is FADH2 produced?

FADH2 is produced during the conversion of succinate to fumarate in the Citric Acid Cycle. This step involves the enzyme succinate dehydrogenase, which catalyzes the oxidation of succinate. During this process, succinate loses two hydrogen atoms, which are transferred to FAD, reducing it to FADH2. This reaction is significant because FADH2 acts as an electron carrier, contributing to the electron transport chain where it eventually helps in the production of ATP.

The other steps mentioned in the options focus on different metabolic conversions within the cycle, but they do not produce FADH2. The conversion of isocitrate to alpha-ketoglutarate produces NADH, as does the conversion of alpha-ketoglutarate to succinyl-CoA. The step of converting fumarate to malate also does not produce FADH2; instead, it involves the reduction of fumarate to malate without FAD being involved. Therefore, the step where succinate converts to fumarate is unique in that it is the only one listed that results in the formation of FADH2.