Britannica Sources used in this answer

What happens during the tricarboxylic acid cycle in mitochondria?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Fluorescent confocal image of HeLa cells with green microtubules outlining cell shapes, red mitochondria, and blue nuclei. — mitochondrion Mitochondria (red) are found throughout the cytoplasm of almost all eukaryotic cells (cell nucleus is shown in blue; cytoskeleton is shown in yellow).

The tricarboxylic acid (TCA) cycle, also known as the citric acid cycle, is the second stage of cellular respiration and occurs within the matrix of the mitochondrion.

During this cycle, acetyl coenzyme A (acetyl CoA)—derived from the breakdown of sugars, fats, and amino acids—is converted into carbon dioxide and energy. The process involves eight enzymatic steps that ultimately regenerate oxaloacetate, allowing the cycle to repeat.1

Key outcomes of the cycle include:
* Energy Production: One molecule of ATP is produced directly per turn.1
* Electron Donation: Most energy is captured by reducing NAD+ to NADH and FAD to FADH2.12
* Oxidation: These electron carriers subsequently transfer their energy to the electron transport chain, where it is used to generate further ATP through oxidative phosphorylation.12

By processing these metabolic fragments, the mitochondrion efficiently harvests energy while releasing carbon dioxide as a byproduct.12