The citric acid cycle, also known as the Krebs cycle or tricarboxylic acid (TCA) cycle, is a central metabolic pathway that completes the oxidation of glucose derivatives to produce energy-rich molecules. Understanding the exact yield of products per cycle and per glucose molecule is essential for grasping cellular energy production.

This article details the typical products formed during the citric acid cycle and clarifies the quantities generated per glucose molecule.

Citric Acid Cycle Overview

• The cycle takes place in the mitochondrial matrix.

• Each acetyl-CoA molecule entering the cycle produces specific amounts of reduced coenzymes and high-energy molecules.

• Since one glucose molecule produces two molecules of pyruvate during glycolysis, and each pyruvate yields one acetyl-CoA, the cycle turns twice per glucose.

Products per One Turn of the Citric Acid Cycle

For one acetyl-CoA molecule (one turn of the cycle), the products are:

• 1 GTP (or ATP)

• 3 NADH

• 1 FADH₂

• 2 CO₂ molecules (released as waste)

Products per One Molecule of Glucose

Since one glucose yields two acetyl-CoA molecules, the total products per glucose are:

• 2 GTP (or ATP)

• 6 NADH

• 2 FADH₂

• 4 CO₂ molecules

These reduced coenzymes (NADH and FADH₂) feed electrons into the electron transport chain, driving the production of the majority of ATP during oxidative phosphorylation.

Evaluating the Given Options

Option (1) correctly states the products for one turn of the cycle (one acetyl-CoA), which is the standard way to describe the citric acid cycle yield.

Conclusion

The citric acid cycle produces 1 GTP, 3 NADH, 1 FADH₂, and 2 CO₂ molecules per acetyl-CoA molecule oxidized. Since each glucose yields two acetyl-CoA molecules, these amounts double per glucose molecule.

Correct answer: (1) 1 GTP, 3 NADH, 1 FADH2, 2 CO2