The tricarboxylic acid (TCA) cycle, also known as the citric acid or Krebs cycle, is a fundamental metabolic pathway that oxidizes acetyl-CoA to generate energy-rich molecules essential for ATP synthesis. These molecules—NADH, FADH2, and GTP—drive the electron transport chain and oxidative phosphorylation, producing the bulk of cellular energy.

This article clarifies the exact combination of energy-rich molecules produced during one turn of the TCA cycle.

Products of One Turn of the TCA Cycle

For each molecule of acetyl-CoA entering the TCA cycle, the following are produced:

• 3 NADH molecules: Generated during the oxidation steps converting isocitrate to α-ketoglutarate, α-ketoglutarate to succinyl-CoA, and malate to oxaloacetate.

• 1 FADH2 molecule: Produced during the oxidation of succinate to fumarate.

• 1 GTP molecule: Formed via substrate-level phosphorylation during the conversion of succinyl-CoA to succinate.

• 2 CO2 molecules: Released as waste during decarboxylation steps.

These reduced coenzymes (NADH and FADH2) transfer electrons to the electron transport chain, driving ATP synthesis.

Evaluating the Given Options

Summary Table

Conclusion

The TCA cycle produces 1 GTP, 3 NADH, and 1 FADH2 per molecule of acetyl-CoA metabolized. This combination is essential for the generation of ATP through oxidative phosphorylation.

Correct answer: (3) 1 GTP, 3 NADH and 1 FADH2