The citric acid cycle is the hub of the metabolism, a central wheel from which many spokes radiate. Also known as the tricarboxylic acid cycle (TCA) or Krebs cycle, it is the final common pathway for the oxidative degradation of fuel molecules and also the source of many biosynthetic precursors. As a degradative pathway, the cycle results stoichiometrically in the complete oxidation of an activated acetyl unit to CO2. With each turn of the cycle three NAD+ molecules and one FAD molecule are reduced which may subsequently donate their electrons to the electron transport system of the mitochondrial matrix, producing ATP. Additionally, with each turn of the cycle, one high energy phosphate bond is created by direct substrate level phosphorylation.
Conceptual Vocabulary for The Citric Acid Cycle