This animation shows the reactions of the citric acid cycle, which splits off carbon atoms and generates energy-rich reduced forms of cofactor molecules. It is the first of three animations about cellular respiration. These animations bring to life the molecular engines inside mitochondria that generate ATP, the main source of chemically stored energy used throughout the body.
 
The citric acid cycle is a key component of cellular respiration. The citric acid cycle gains two carbon atoms from glycolysis, and those atoms are split off one by one to be released as carbon dioxide. The reactions release chemical energy, which is captured as energy-rich reduced forms of cofactors. These cofactors provide the chemical energy for the electron transport chain (shown in the second animation), which is the next stage of cellular respiration. The citric acid cycle also produces many intermediate molecules that are precursors to important biological molecules.
 
The animation is appropriate for teaching advanced high school or college-level students the in-depth mechanisms of the citric acid cycle. For more general audiences, the animation can be used as an example of molecular machines and enzymes in action. Depending on students’ background, it may be helpful to pause the animation at various points to discuss different reactions or molecules. 

All three cellular respiration animations are also available in a YouTube playlist.

An audio descriptive version of the film is available via our media player.