Krebs Cycle also known as the tricarboxylic acid cycle (TCA),was first recognized in 1937 by the German biochemist named, Hans Adolph Krebs. The Krebs cycle produces carbon dioxide and a compound rich in energy, Adenosine triphosphate (ATP). This chemical provides cells with the energy required for the synthesis of proteins from amino acids and the replication of deoxyribonucleic acid (DNA). Krebs cycle, energy in the form of ATP is usually derived from the breakdown of glucose A. Release of two moles of CO2 and regeneration of one mole of OAA for oxidation of one acetyl CoA; most of the CO2 from the body metabolism produce this way. B. Generation of 1 molecules of ATP via oxidation phosphorylation. C. Production of one equivalent of high-energy phosphate as guanosine triphosphate(GTP) A. Intermediates also serve as substrate for biosynthetic pathways and thus need to be replenished B. Anaplerotic reaction provides OAA or other cycle intermediates. 1. Pyruvate carboxylase in the liver and kidney Pyruvate + ATP+ HCO3 OAA + ADP +P 2. Phosphoenolpyruvate (PEP) carboxykinase in the heart and skeletal muscle Phosphoenolpyruvate + CO2 +GDP OAA +GTP 3. Malic enzyme in many tissue Pyruvate + HCO3 + NAD(P) Malate + NAD(P) 4. Glutamate dehydrogenase in the liver Glutamate+ NAD(P) + H2O a-ketoglutarate + NAD(P)+NH4 A. Accetyl CoA condense with OAA to form citrate A. Enzyme: citrate synthase. B. ATP, an allosteric inhibitor, increases the Km for accetyl CoA, one of the substrates. B. Isocitrate is oxidize to a-ketoglutarate. A. Enzyme: iscocitrate dehydrogenase. B. ADP in an allosteric activator, and ATP and NADH are inhibitor C. a-ketoglutarate is coverted to succinyl CoA A. Enzyme: a – ketoglutarate dehydrogenase B. Succinyl CoA and NADH are inhibitor e n d .