Biochemistry and Molecular Biology - Belyasova, N. A. 2002

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

Fig. 11.6 illustrates that each turn of The Tricarboxylic Acid Cycle involves The entry of two carbon atoms (as an acetyl-CoA molecule) and the release of two carbon atoms (as two molecules of CO2). Carbon reaches its highest oxidation state in the CO2 molecule.

The oxidation of carbon is accompanied by the removal of four pairs of hydrogen atoms from the TCA cycle intermediates. This results in the reduction of 3 molecules of NAD+ and 1 molecule of FAD, yielding 3 molecules of NADH and 1 molecule of FADH2. The regeneration of the oxidized forms of these reducing equivalent carriers takes place in the Respiratory Chain, where molecular oxygen serves as the terminal electron acceptor. Consequently, the TCA cycle Functions exclusively under aerobic conditions, even though molecular oxygen is not directly consumed in the cycle's reactions.

Each turn of the TCA cycle provides energy storage via substrate-level phosphorylation, resulting in the synthesis of one ATP (or GTP) molecule.

The overall Stoichiometry of the TCA cycle is:

Class="center">Ацетил-СоА + 3NAD+ + FAD + ADP + Pi + 2H2O →

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



Last update: 06/08/2026

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