The tricarboxylic acid cycle (Krebs cycle, citric acid cycle) is a focal end point for the oxidation of carbohydrate, fat and amino acids via acetyl coenzyme A. Pyruvate is converted to acetyl coenzyme A by the pyruvate dehydrogenase complex. The reactions of the TCA cycle generate carbon dioxide, reduced NAD, reduced FAD and GTP* There are negative and positive controls for the TCA cycle *Guanosine triphosphate (GTP) is a guanine nucleotide containing three phosphate groups esterified to the sugar moiety. GTP functions as a carrier of phosphates and pyrophosphates involved in channeling chemical energy into specific biosynthetic pathways.