Glyoxylate cycle: Difference between revisions

Latest revision as of 11:59, 15 February 2025

Glyoxylate Cycle[edit]

The glyoxylate cycle is a series of biochemical reactions that enables certain organisms, such as plants, bacteria, and fungi, to convert fatty acids into carbohydrates. This cycle is a variation of the citric acid cycle and is crucial for organisms that rely on stored lipids as a carbon source, especially during seed germination in plants.

Overview[edit]

The glyoxylate cycle bypasses the decarboxylation steps of the citric acid cycle, allowing the conversion of acetyl-CoA into four-carbon dicarboxylic acids, which can then be used for gluconeogenesis. This cycle takes place in specialized peroxisomes known as glyoxysomes in plants and in the cytoplasm of some bacteria.

Key Enzymes[edit]

The glyoxylate cycle involves several key enzymes:

Isocitrate lyase: This enzyme catalyzes the cleavage of isocitrate into succinate and glyoxylate.
Malate synthase: This enzyme catalyzes the condensation of glyoxylate and acetyl-CoA to form malate.

These enzymes allow the cycle to bypass the steps in the citric acid cycle that release carbon dioxide, thus conserving carbon atoms for the synthesis of carbohydrates.

Biological Significance[edit]

The glyoxylate cycle is particularly important in:

Seed Germination: In plants, the glyoxylate cycle is active in the early stages of seed germination, when the seedling relies on stored lipids for energy and carbon skeletons until it can perform photosynthesis.
Microbial Growth: Some bacteria and fungi use the glyoxylate cycle to grow on acetate or other simple carbon compounds as their sole carbon source.

Differences from the Citric Acid Cycle[edit]

The main differences between the glyoxylate cycle and the citric acid cycle are:

The glyoxylate cycle bypasses the two decarboxylation steps of the citric acid cycle, preventing the loss of carbon as carbon dioxide.
It includes the unique enzymes isocitrate lyase and malate synthase.

Related Pages[edit]

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-'''Glyoxylate cycle''' is a metabolic pathway that occurs in many bacteria, plants, and fungi. It is a variation of the [[Citric acid cycle|citric acid cycle]] and allows these organisms to survive on [[Acetate|acetate]] or [[Fatty acid|fatty acids]] as the sole carbon source. The glyoxylate cycle bypasses the decarboxylation steps of the citric acid cycle and, thus, conserves the carbons of isocitrate to form glyoxylate and succinate.
+== Glyoxylate Cycle ==
-== Overview ==
+[[File:Glyoxylatepath.svg|thumb|right|Diagram of the glyoxylate cycle]]
-The glyoxylate cycle begins in the [[Mitochondria|mitochondria]], where two molecules of acetyl-CoA condense to form citrate via the enzyme [[Citrate synthase|citrate synthase]]. This citrate is then converted to isocitrate by [[Aconitase|aconitase]].
+The '''glyoxylate cycle''' is a series of biochemical reactions that enables certain organisms, such as plants, bacteria, and fungi, to convert [[fatty acids]] into [[carbohydrates]]. This cycle is a variation of the [[citric acid cycle]] and is crucial for organisms that rely on stored lipids as a carbon source, especially during seed germination in plants.
-In the next step, isocitrate is converted into glyoxylate and succinate by the enzyme [[Isocitrate lyase|isocitrate lyase]]. This is the first unique step of the glyoxylate cycle. The glyoxylate is then condensed with another molecule of acetyl-CoA to form malate, catalyzed by the enzyme [[Malate synthase|malate synthase]]. This is the second unique step of the glyoxylate cycle.
+=== Overview ===
+The glyoxylate cycle bypasses the decarboxylation steps of the citric acid cycle, allowing the conversion of acetyl-CoA into four-carbon dicarboxylic acids, which can then be used for gluconeogenesis. This cycle takes place in specialized peroxisomes known as [[glyoxysomes]] in plants and in the [[cytoplasm]] of some bacteria.
-The malate is then converted back to oxaloacetate by [[Malate dehydrogenase|malate dehydrogenase]], completing the cycle. The oxaloacetate can then be used to initiate another round of the cycle.
+=== Key Enzymes ===
+The glyoxylate cycle involves several key enzymes:
-== Role in Organisms ==
+* '''[[Isocitrate lyase]]''': This enzyme catalyzes the cleavage of [[isocitrate]] into [[succinate]] and [[glyoxylate]].
+* '''[[Malate synthase]]''': This enzyme catalyzes the condensation of glyoxylate and [[acetyl-CoA]] to form [[malate]].
-The glyoxylate cycle is crucial for many organisms as it allows them to grow on acetate or fatty acids as the sole carbon source. This is particularly important for plants and fungi, which often have to survive in environments where carbohydrates are scarce.
+These enzymes allow the cycle to bypass the steps in the citric acid cycle that release carbon dioxide, thus conserving carbon atoms for the synthesis of carbohydrates.
-== See Also ==
+=== Biological Significance ===
+The glyoxylate cycle is particularly important in:
+* '''Seed Germination''': In plants, the glyoxylate cycle is active in the early stages of seed germination, when the seedling relies on stored lipids for energy and carbon skeletons until it can perform [[photosynthesis]].
+* '''Microbial Growth''': Some bacteria and fungi use the glyoxylate cycle to grow on acetate or other simple carbon compounds as their sole carbon source.
+=== Differences from the Citric Acid Cycle ===
+The main differences between the glyoxylate cycle and the citric acid cycle are:
+* The glyoxylate cycle bypasses the two decarboxylation steps of the citric acid cycle, preventing the loss of carbon as carbon dioxide.
+* It includes the unique enzymes isocitrate lyase and malate synthase.
+== Related Pages ==
 * [[Citric acid cycle]]
-* [[Acetate]]
+* [[Gluconeogenesis]]
-* [[Fatty acid]]
+* [[Peroxisome]]
-* [[Mitochondria]]
+* [[Metabolism]]
-* [[Citrate synthase]]
-* [[Aconitase]]
-* [[Isocitrate lyase]]
-* [[Malate synthase]]
-* [[Malate dehydrogenase]]
 [[Category:Metabolic pathways]]
-[[Category:Biochemistry]]
-[[Category:Microbiology]]
-[[Category:Plant physiology]]
-[[Category:Fungal physiology]]
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-{{dictionary-stub1}}