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Overview of the citric acid cycle. 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 reverse Krebs cycle, also known as the reverse TCA cycle (rTCA) or reductive citric acid cycle, is an alternative to the standard Calvin-Benson cycle for carbon fixation. It has been found in strict anaerobic or microaerobic bacteria (as Aquificales ) and anaerobic archea .
To fully oxidize the equivalent of one glucose molecule, two acetyl-CoA must be metabolized by the Krebs cycle. Two low-energy waste products, H 2 O and CO 2, are created during this cycle. [12] [13] The citric acid cycle is an 8-step process involving 18 different enzymes and co-enzymes.
English: Tricarboxylic acid cycle (also known as the citric acid cycle) and some preceding steps Español : Ciclo del ácido cítrico (Ciclo de Krebs). Esperanto : Ciklo de Krebs (ankaux konata kiel citr-acida ciklo).
The metabolites are for each turn of the Krebs cycle. The Krebs cycle turns twice for each six-carbon molecule of glucose that passes through the aerobic system – as two three-carbon pyruvate molecules enter the Krebs cycle. Before pyruvate enters the Krebs cycle it must be converted to acetyl coenzyme A.
Pyruvate oxidation is the step that connects glycolysis and the Krebs cycle. [4] In glycolysis, a single glucose molecule (6 carbons) is split into 2 pyruvates (3 carbons each). Because of this, the link reaction occurs twice for each glucose molecule to produce a total of 2 acetyl-CoA molecules, which can then enter the Krebs cycle.
[32] [33] It is also known as the "Krebs cycle" or "tricarboxylic acid (TCA) cycle". Krebs sent a short manuscript account of the discovery to Nature on 10 June 1937. On 14 June, he received a rejection letter from the editor, saying that the journal had "already sufficient letters to fill correspondence columns for seven or eight weeks", and ...
Pyruvate decarboxylation is the step that connects glycolysis and the Krebs cycle and is regulated by the pyruvate dehydrogenase complex when blood glucose levels are high. [9] Otherwise, fatty acid β-oxidation occurs, and acetyl-CoA is required to generate ATP through the Krebs cycle. [10]