Metabolic pathway
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In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell, catalyzed by enzymes, to achieve in either the formation of a metabolic product to be used or stored by the cell, or the initiation of another metabolic pathway (then called a flux generating step). Many of these pathways are elaborate, and involve a step by step modification of the initial substance to shape it into the product with the exact chemical structure desired.
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Overview
Most metabolic pathways have these common properties:
- They are irreversible, usually because the first step is a committed step, such breakdown for the release of energy, that only runs in one direction.
- The pathways are regulated, usually by feedback inhibition, or may be a cycle where the end product starts the reaction again, such as the Krebs Cycle (see below).
- Anabolic and catabolic pathways in eukaryotes are separated by either compartmentation or by the use of different enzymes and cofactors.
Major metabolic pathways
Cellular respiration
Main article: Cellular respiration
Several distinct but linked metabolic pathways are used by cells to transfer the energy released by breakdown of fuel molecules to ATP:
Other pathways
- Fatty acid oxidation (β-oxidation)
- Gluconeogenesis
- HMG-CoA reductase pathway (cholesterol, isoprene prenylation chains)
- Pentose phosphate pathway (hexose monophosphate shunt)
- Porphyrin synthesis (or heme synthesis) pathway
- Urea cycle
See also
External links
- Open Directory Project: Metabolic Pathways (http://www.dmoz.org/Science/Biology/Biochemistry_and_Molecular_Biology/Metabolic_Pathways/)
- Metabolism, Cellular Respiration and Photosynthesis - The Virtual Library of Biochemistry and Cell Biology (http://www.biochemweb.org/metabolism.shtml)
- KEGG: Kyoto Encyclopedia of Genes and Genomes (http://www.genome.jp/kegg/)de:Stoffwechselweg