Krebs Cycle occurs in the matrix of the mitochondrion. Major purpose of this lecture is to present on Krebs Cycle. The Krebs Cycle is the central metabolic pathway in all aerobic organisms. Citric acid (6C) is gradually converted back to the 4-carbon compound – ready to start the cycle once more. The carbons removed are released as CO2 – enzymes controlling this process called decarboxylases. The hydrogens, which are removed, join with NAD to form NADH2 – enzymes controlling the release of hydrogen are called dehydrogenases.