General purpose of this lecture is to presentation on Citric Acid Cycle. This lecture briefly explain on Pyruvate Dehydrogenase Complex (PDC) and its control, Reactions of TCA cycle or CAC and Amphibolic nature of TCA cycle. Here also analysis Regulation of TCA cycle. Finally discuss whereas pyruvate dehydrogenase and TCA cycle reactions take place in mitochondria where oxygen is utilized to generate ATP by oxydative phosphorylation. Another observation is Consumption of oxygen (respiration) depends on the rate of PDC and TCA reactions.