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It is the second of three metabolic pathways that are involved in fuel molecule catabolism and ATP production.
The citric acid cycle also provides precursors for many compounds such as certain amino acids, and some of its reactions are therefore important even in cells performing fermentationIn its strictest sense fermentation is the energy-yielding anaerobic metabolic breakdown of a nutrient molecule, such as glucose, without net oxidation. Fermentation yields lactate, acetic acid, ethanol, or some other simple product. Fermentation is also.
The citric acid cycle is also known as the Krebs cycle after Sir Hans Adolf KrebsSir Hans Adolf Krebs ( August 25, 1900 November 22, 1981) was a German medical doctor and biochemist. He was born in Hildesheim, Germany, the son of Georg Krebs, also M. and his wife Alma. He went to school in Hildesheim and studied medicine at the Univer (1900-1981), who proposed the key elements of this pathway in 1937 and was awarded the Nobel Prize in MedicineList of Nobel Prize laureates in Physiology or Medicine from 1901 to the present day. 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s External links http://www. se/medicin for its discovery in 19531953 is a common year starting on Thursday (click on link for the calendar). Events January events January 7 President Harry S. Truman announces the United States has developed a hydrogen bomb. January 13 Marshal Josip Broz Tito chosen President of Yugosl.
The citric acid cycle takes place within the mitochondria in eukaryoteEukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. They include the animals, plants, and fungi, which are mostly multicellular, as well as various other groups called protists, many of whichs, and within the cytoplasmCytoplasm is the viscid, semifluid matter contained within the plasma membrane of a cell that helps to hold the cell together. In contrast to the protoplasm, however, the cytoplasm does not include the cell nucleus. The watery or aqueous component of the in prokaryoteProkaryotes are mostly unicellular organisms without a nucleus, in contrast to eukaryotes, organisms that have cell nuclei and may be variously unicellular or multicellular. The difference between prokaryote and eukaryote cell structure is the most imports.
Fuel molecule catabolism (including glycolysis) produces acetyl-CoA, a two- carbon acetyl group bound to coenzyme A. Acetyl-CoA is the main input to the citric acid cycle. Citrate is both the first and the last product of the cycle (Fig 1), and is regenerated by the condensation of oxaloacetate and acetyl-CoA.
| Molecule | Enzyme | Reaction type | Reactants/ Coenzymes | Products/ Coenzymes |
|---|---|---|---|---|
| I. Citrate | 1. Aconitase | Dehydration | H2O | |
| II. cis- Aconitate | 2. Aconitase | Hydration | H2O | |
| III. Isocitrate | 3. Isocitrate dehydrogenase | Oxidation | NAD+ | NADH + H+ |
| IV. Oxalosuccinate | 4. Isocitrate dehydrogenase | Decarboxylation | ||
| V. α- Ketoglutarate | 5. α-Ketoglutarate dehydrogenase | Oxidative decarboxylation | NAD+ + CoA-SH | NADH + H+ + CO2 |
| VI. Succinyl-CoA | 6. Succinyl-CoA synthetase | Hydrolysis | GDP + Pi | GTP + CoA-SH |
| VII. Succinate | 7. Succinate dehydrogenase | Oxidation | FAD | FADH2 |
| VIII. Fumarate | 8. Fumarase | Addition ( H2O) | H2O | |
| IX. L- Malate | 9. Malate dehydrogenase | Oxidation | NAD+ | NADH + H+ |
| X. Oxaloacetate | 10. Citrate synthase | Condensation | ||
| XI. Acetyl-CoA |
The sum of all reactions in the citric acid cycle is:
Two carbons are oxidized to CO2, and the energy from these reactions is stored in ATP (ATP is the "universal energy currency" of the cell), NADH and FADH2. NADH and FADH2 are coenzymes (molecules that enable or enhance enzymes) that store energy and can release it when needed.
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