Glyoxylate cycle: Difference between revisions
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'''The glyoxylate cycle''' is a [[metabolic pathway]] occurring in [[plant]]s and several [[microorganism]]s which allows them to use [[acetyl CoA]]s for the synthesis of [[carbohydrate]]s, a task which [[vertebrate]]s, including [[human]]s, cannot perform. | '''The glyoxylate cycle''' is a [[metabolic pathway]] occurring in [[plant]]s and several [[microorganism]]s which allows them to use [[acetyl CoA]]s for the synthesis of [[carbohydrate]]s, a task which [[vertebrate]]s, including [[human]]s, cannot perform. | ||
The two initial stages of this cycle are identical to those of the citric acid cycle: ''' | The two initial stages of this cycle are identical to those of the citric acid cycle: '''acetyl-CoA → citrate → isocitrate'''. The next step, however, is different: isocitrate is cleaved into [[succinate]] and glyoxylate (the latter gives the cycle its name). Succinate can be channeled directly into the citric acid cycle and eventually form oxaloacetate. Glyoxylate condenses with acetyl-CoA, yielding [[malate]]. Both [[malate]] and [[oxaloacetate]] can be converted into [[phosphoenolpyruvate]] and enter [[gluconeogenesis]]. The net result of the glyoxylate cycle is therefore the production of glucose from [[acetyl CoA]]. | ||
In plants the glyoxylate cycle occurs in special [[peroxisome]]s which are called [[glyoxysome]]s. Vertebrates cannot perform the cycle because they lack its two key [[enzyme]]s: isocitrate [[lyase]] and [[malate]] [[synthase]]. | In plants the glyoxylate cycle occurs in special [[peroxisome]]s which are called [[glyoxysome]]s. Vertebrates cannot perform the cycle because they lack its two key [[enzyme]]s: isocitrate [[lyase]] and [[malate]] [[synthase]]. | ||
Revision as of 08:51, 19 December 2006
The glyoxylate cycle is a metabolic pathway occurring in plants and several microorganisms which allows them to use acetyl CoAs for the synthesis of carbohydrates, a task which vertebrates, including humans, cannot perform. The two initial stages of this cycle are identical to those of the citric acid cycle: acetyl-CoA → citrate → isocitrate. The next step, however, is different: isocitrate is cleaved into succinate and glyoxylate (the latter gives the cycle its name). Succinate can be channeled directly into the citric acid cycle and eventually form oxaloacetate. Glyoxylate condenses with acetyl-CoA, yielding malate. Both malate and oxaloacetate can be converted into phosphoenolpyruvate and enter gluconeogenesis. The net result of the glyoxylate cycle is therefore the production of glucose from acetyl CoA.
In plants the glyoxylate cycle occurs in special peroxisomes which are called glyoxysomes. Vertebrates cannot perform the cycle because they lack its two key enzymes: isocitrate lyase and malate synthase.