The Citric Acid Cycle is also known as the Krebs cycle or Tricarboxylic Acid (TCA) Cycle. It is a series of chemical reactions that takes place in the cell that breaks down food molecules into carbon dioxide, water, and energy.
In order for food to enter the citric acid cycle, it must be broken into acetyl groups, (CH3CO). At the start of the citric acid cycle, an acetyl group combines with a four-carbon molecule called oxaloacetate to make a six-carbon compound, citric acid. During the cycle, the citric acid molecule is rearranged and stripped of two of its carbon atoms. Carbon dioxide and 4 electrons are released. At the end of the cycle, a molecule of oxaloacetate remains, which can combine with another acetyl group to being the cycle again.