Major metabolic pathways converging on the citric acid cycle

spinqualitylabelsall models Crystal structure of the biotin carboxylase subunit of pyruvate carboxylase (PDB code 1ulz) Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Under development! The Citric Acid Cycle is a key metabolic pathway that connects carbohydrate, fat, and protein metabolism!!! See also [1], Krebs cycle importance, and Citric acid cycle intermediates serve as substrates for biosynthetic processes. Several catabolic pathways converge on the citric acid cycle. Most of these reactions add intermediates to the citric acid cycle, and are therefore known as anaplerotic reactions, from the Greek meaning to "fill up". These increase the amount of acetyl CoA that the cycle is able to carry, increasing the mitochondrion's capability to carry out respiration if this is otherwise a limiting factor. Processes that remove intermediates from the cycle are termed "cataplerotic" reactions. Pyruvate molecules produced by glycolysis are actively transported across the inner mitochondrial membrane, and into the matrix. Here they can be oxidized and combined with coenzyme A to form CO2, acetyl-CoA, and NADH, as in the normal cycle. However, it is also possible for pyruvate to be carboxylated by Pyruvate carboxylase to form oxaloacetate. This latter reaction "fills up" the amount of oxaloacetate in the citric acid cycle, and is therefore an anaplerotic reaction, increasing the cycle's capacity to metabolize acetyl-CoA when the tissue's energy needs (e.g. in muscle) are suddenly increased by activity. The succinyl-CoA formed during Beta oxidation can enter the Citric Acid Cycle. See also: Biosynthesis of cholesterol Fatty acid synthesis

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