Biochemistry and Molecular Biology - Belyasova N.A. 2002

Metabolism. Processes Leading to Energy Storage
Tricarboxylic Acid Cycle
TCA Cycle Balance

Figure 11.6 shows that each turn of The Tricarboxylic Acid Cycle is accompanied by The entry of two carbon atoms (as an acetyl-CoA molecule) and the release of two carbon atoms (as two CO2 molecules). In the CO2 molecule, carbon reaches its highest oxidation state.

Carbon oxidation is accompanied by the removal of four pairs of hydrogen atoms from the TCA cycle intermediates. This is accompanied by the reduction of 3 NAD+ molecules and 1 FAD molecule, yielding 3 NADH molecules and 1 FADH2 molecule. Regeneration of the oxidized forms of reducing equivalent carriers occurs in the Respiratory Chain, where molecular oxygen serves as the terminal electron acceptor. Therefore, the TCA cycle Functions only under aerobic conditions, even though molecular oxygen does not directly participate in the Reactions of the cycle.

Each turn of the TCA cycle ensures energy conservation via substrate-level phosphorylation: one ATP (or GTP) molecule is synthesized.

Overall Stoichiometry of the TCA cycle:

Class="center">Acetyl-CoA + 3NAD+ + FAD + ADP + Pi + 2H2O →

→ 2CO2 + 3NADH + FADH2 + ATP + 2H+ + CoA



Last update: 06/08/2026

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