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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 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. [9] [10] The citric acid cycle is an 8-step process involving 18 different enzymes and co-enzymes.
After four months of experimental works to fill in the gaps, Krebs and Johnson succeeded in establishing the sequence of the chemical cycle, which they called the "citric acid 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 ...
Amphibolic properties of the citric acid cycle. An amphibolic pathway is one that can be either catabolic or anabolic based on the availability of or the need for energy. [10]: 570 The currency of energy in a biological cell is adenosine triphosphate (ATP), which stores its energy in the phosphoanhydride bonds. The energy is utilized to conduct ...
The energy stored in the chemical bonds of glucose is released by the cell in the citric acid cycle, producing carbon dioxide and the energetic electron donors NADH and FADH. Oxidative phosphorylation uses these molecules and O 2 to produce ATP , which is used throughout the cell whenever energy is needed.
It functions as a pace-making enzyme in the first step of the citric acid cycle (or Krebs cycle). [5] Citrate synthase is located within eukaryotic cells in the mitochondrial matrix, but is encoded by nuclear DNA rather than mitochondrial. It is synthesized using cytoplasmic ribosomes, then transported into the mitochondrial matrix.
The citric acid cycle is an example of a metabolon that facilitates substrate channeling. [ 1 ] [ 2 ] Another example is the dhurrin synthesis pathway in sorghum, in which the enzymes assemble as a metabolon in lipid membranes. [ 3 ]