Tricarboxylic Acid Cycle

Abstract

Tricarboxylic acid (TCA) cycle, also known as citric acid cycle and Krebs’ cycle, is the final step in complete oxidation of glucose under aerobic conditions. During aerobic respiration, pyruvate is oxidized to acetyl CoA by the action of the pyruvate dehydrogenase enzyme complex. The acetyl CoA thus generated enters the citric acid cycle. Tricarboxylic acid cycle starts with the condensation of acetyl CoA and oxaloacetate to form citrate and proceeds in a cyclic manner generating reductant, GTP and re-generating oxaloacetate. For complete oxidation of glucose, two rounds of TCA cycle are required. Various intermediates of the TCA cycle which act as precursors for various biosynthetic pathways such as synthesis of amino acids, heme, fats and lipids are discussed. Various reactions required for replenishing oxaloacetate for continuity of the TCA cycle are described. At the end, regulation of the TCA cycle is also discussed.