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The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle) [1] [2] —is a series of biochemical reactions to release the energy stored in nutrients through the oxidation of acetyl-CoA derived from carbohydrates, fats, proteins, and alcohol.
The Reductive/Reverse TCA Cycle (rTCA cycle). Shown are all of the reactants, intermediates and products for this cycle. The reverse Krebs cycle (also known as the reverse tricarboxylic acid cycle, the reverse TCA cycle, or the reverse citric acid cycle, or the reductive tricarboxylic acid cycle, or the reductive TCA cycle) is a sequence of chemical reactions that are used by some bacteria and ...
A simple branch pathway with all reactions irreversible containing just two elementary modes. Because both and are irreversible, and elementary mode lying on both these reactions is not possible since it would mean one reactions going against its thermodynamic direction. Each mode in this system satisfies the three conditions described above.
This final step is highly regulated and deliberately irreversible because pyruvate is a crucial intermediate building block for further metabolic pathways. [17] Once pyruvate is produced, it either enters the TCA cycle for further production of ATP under aerobic conditions, or is converted to lactic acid or ethanol under anaerobic conditions.
[5]: 572 To the right is an illustration of the amphibolic properties of the TCA cycle. The glyoxylate shunt pathway is an alternative to the tricarboxylic acid (TCA) cycle, for it redirects the pathway of TCA to prevent full oxidation of carbon compounds, and to preserve high energy carbon sources as future energy sources. This pathway occurs ...
In this scheme, enzyme c catalyzes the committed step in the biosynthesis of compound 6. In biochemistry , the committed step (also known as the first committed step ) is an effectively irreversible , enzyme - catalyzed reaction that occurs at a branch point during the biosynthesis of some molecules .
Common name IUPAC name Molecular formula Structural formula citric acid: 2-hydroxypropane-1,2,3-tricarboxylic acid: C 6 H 8 O 7: isocitric acid: 1-hydroxypropane-1,2,3-tricarboxylic acid
The pathway uses a different enzyme for each direction for the irreversible step in the pathway, allowing independent regulation of catabolism and anabolism. Due their inherent duality, amphibolic pathways represent the regulation modes of both anabolic by its negative feedback end product and catabolic by feedback by energy indicator sequences.