why tca cycle is called amphibolic pathway

The Citric acid cycle (aka Kreb's cycle and Tricarboxylic acid cycle-TCA cycle) is a sequence of reactions, of an amphibolic overall nature (both catatbolic and anabolic), occurring in mitochondrial matrix that oxidizes acetyl moieties of acetyl-CoA. It is the final common pathway for oxidation of carbohydrate, protein and lipids as glucose, fatty acids and amino acids are metabolized to acetyl-CoA or intemediates of the cycle. The cycle starts with anabolic condensation of acetyl-CoA (3C) and oxaloacetate(3C), to yield citric acid (6C), the tricarboxylic acid of the cycle. In the subsequent catabolic reactions two molecules of CO
are released (in the isocitrate dehydrogenase and a-ketoglutarate dehydrogenase complex steps) and oxaloacetate is regenerated, commencing another cycle.

The enzymes of the cycle are located in the mitochondrial matrix either free or bound to the inner mitochondrial membrane where the enzymes of the respiratory chain and oxidative phosphorylation are also found. The molecule citrate is a prochiral molecule, and in order to generate it, oxaloacetate must first bind to citrate synthase, followed by an incoming acetyl CoA. Cellular respiration Cellular respiration is a process in which cellular energy is generated through the oxidation of nutrient molecules, with oxygen as the ultimate electron acceptor.

Stages of cellular respiration There are two stages of cellular respiration. In stage I, pyruvate is converted to acetyl CoA with the help of pyruvate dehydrogenase complex by oxidative Decarboxylation. Coenzyme A activates acetyl group derived from pyruvate. In stage II, acetyl CoA enters the TCA cycle and gets oxidized through 8 steps, generating ATPs. The Citric acid cycle TCA cycle is a cyclic pathway and the subcellular site of the reaction is mitochondria in eukaryotes. Formation of citrate, then, isocitrate, oxidation of isocitrate, oxidation of ketoglutarate, conversion of succinyl CoA to succinate, oxidation of succinate, hydration of fumarate, oxidation of malate to oxaloacetate.

They are the 8 steps of TCA cycle. Net ATP gain from one glucose molecule is 38. Phases of reactions of citric acid cycle Amphibolic pathway is the metabolic pathway used in both catabolism and anabolism. TCA cycle acts as an amphibolic pathway since it is involved in both breakdown as well as synthesis of biomolecules. There are Anaplerotic reactions which replenish the supply of intermediates in the citric acid cycle. Ex: Malate is formed from pyruvate by the malic enzyme.

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