The primary electron carriers that function in the citric acid cycle are NAD+ (Nicotinamide adenine dinucleotide) and FAD (Flavin adenine dinucleotide).
During the cycle, NAD+ is reduced to NADH when it accepts electrons and a proton during the oxidation of isocitrate to alpha-ketoglutarate and again during the conversion of malate to oxaloacetate. Similarly, FAD is reduced to FADH2 when succinate is oxidized to fumarate.
These carriers play a crucial role in the electron transport chain, where the electrons they carry are ultimately used to generate ATP, the energy currency of the cell. By transferring electrons derived from the oxidation of carbohydrates, fats, and proteins, NADH and FADH2 link the citric acid cycle to cellular respiration, making them essential for energy production in aerobic organisms.