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'''Carbohydrate metabolism''' denotes the various [[biochemistry|biochemical]] processes responsible for the [[anabolism|formation]], [[catabolism|breakdown]] and interconversion of [[carbohydrates]] in [[life|living]] [[organism]]s. It includes:
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*[[Carbon fixation]], whereby CO<sub>2</sub> is reduced to carbohydrate.
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{{BioPsy}}
*[[Glycolysis]] - the breakdown of the [[glucose]] molecule in order to obtain [[ATP]]
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*the [[Pentose phosphate pathway]], which acts in the conversion of [[hexose]]s into [[pentose]]s and in [[NADPH]] regeneration.
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'''Carbohydrate metabolism''' denotes the various [[biochemistry|biochemical]] processes responsible for the [[anabolism|formation]], [[catabolism|breakdown]] and interconversion of [[carbohydrates]] in [[life|living]] [[organism]]s.
*[[Glycogenesis]] - the conversion of excess glucose into [[glycogen]] in order to prevent excessive [[osmotic pressure]] buildup inside the cell
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*[[Glycogenolysis]] - the breakdown of glycogen into glucose, in order to provide a steady level of glucose supply for glucose-dependent tissues.
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The most important carbohydrate is [[glucose]], a simple sugar ([[monosaccharide]]) that is metabolized by nearly all known organisms. Glucose and other carbohydrates are part of a wide variety of metabolic pathways across species: [[plants]] synthesize carbohydrates from atmospheric gases by [[photosynthesis]], which can then be consumed by other organisms and used as fuel for [[cellular respiration]]. Oxidation of one gram of carbohydrate yields approximately 4 kcal of [[Chemical energy|energy]]. Energy obtained from carbohydrate metabolism is usually stored in the form of [[Adenosine triphosphate|ATP]]. Organisms capable of [[aerobic respiration]] metabolize glucose and [[oxygen]] to release energy with [[carbon dioxide]] and [[water]] as byproducts.
*[[Gluconeogenesis]] - <i>de novo</i> synthesis of glucose molecules from simple [[organic chemistry|organic]] compounds
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All carbohydrates share a general formula of approximately C<sub>n</sub>H<sub>2n</sub>O<sub>n</sub>; glucose is C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>. Monosaccharides may be chemically bonded together to form [[disaccharides]] such as [[sucrose]] and longer [[polysaccharides]] such as [[starch]] and [[cellulose]].
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Carbohydrates are a superior short-term energy reserve for organisms, because they are much simpler to metabolize than [[fats]] or [[proteins]]. In animals, all dietary carbohydrates are delivered to cells in the form of glucose. Carbohydrates are typically stored as long polymers of glucose molecules with [[Glycosidic bond]]s for structural support (e.g. [[chitin]], [[cellulose]]) or energy storage (e.g. [[glycogen]], [[starch]]). However, the strong affinity of carbohydrates for water makes storage of large quantities of carbohydrates inefficient due to the large molecular weight of the solvated water-carbohydrate complex. In some organisms, excess carbohydrates are catabolised to form [[Acetyl-CoA]], where they enter the [[fatty acid synthesis]] pathway. [[Fatty acids]], [[triglycerides]], and other [[lipids]] are commonly used for long-term energy storage. The hydrophobic character of lipids makes them a much more compact form of energy storage than hydrophilic carbohydrates.
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==Catabolism==
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{{Main|Carbohydrate catabolism}}
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Oligo/polysaccharides are cleaved first to smaller monosaccharides by enzymes called [[Glycoside hydrolase]]s. The monosaccharide units can then enter into monosaccharide catabolism.
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==Metabolic pathways==
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* [[Carbon fixation]], whereby CO<sub>2</sub> is reduced to carbohydrate.
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* [[Glycolysis]] - the breakdown of the [[glucose]] molecule in order to obtain [[adenosine triphosphate|ATP]] and [[Pyruvate]]
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** Pyruvate from glycolysis enters the [[Krebs cycle]] in [[aerobic]] organisms.
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* The [[Pentose phosphate pathway]], which acts in the conversion of [[hexose]]s into [[pentose]]s and in [[NADPH]] regeneration.
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* [[Glycogenesis]] - the conversion of excess glucose into [[glycogen]] in order to prevent excessive [[osmotic pressure]] buildup inside the cell
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* [[Glycogenolysis]] - the breakdown of glycogen into glucose, in order to provide a steady level of glucose supply for glucose-dependent tissues.
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* [[Gluconeogenesis]] - ''de novo'' synthesis of glucose molecules from simple [[organic chemistry|organic]] compounds
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==Glucoregulation==
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Glucoregulation is the maintenance of steady levels of [[glucose]] in the body; it is part of [[homeostasis]], and keeps a constant internal environment around cells in the body.
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The hormone [[insulin]] makes the body convert glucose into glycogen and puts it into the liver; the insulin is made in the pancreas, and is secreted when the blood sugar is too high. Insulin also promotes the use of glucose by the muscles.
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The hormone [[glucagon]], on the other hand, acts in the opposite direction and promotes the conversion of glycogen to glucose in response to low blood sugar.
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==Human diseases of carbohydrate metabolism==
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* [[Diabetes mellitus]]
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* [[Lactose intolerance]]
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* [[Fructose intolerance]]
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* [[Galactosemia]]
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* [[Glycogen storage disease]]
   
 
==See also==
 
==See also==
{{metabolism}}
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*[[Acetaldrhyde]]
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*[[Guanosine]]
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*[[Glucose metabolism]]
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==External links==
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* {{MeshName|Carbohydrate+metabolism}}
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*[http://diabetescorner.blogspot.com/2007/09/glucose-metabolism.html Glucose Metabolism and Diabetes]
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*[http://www.bbc.co.uk/schools/gcsebitesize/biology/humansasorganisms/6homeostasisrev4.shtml BBC - GCSE Bitesize - Biology | Humans | Glucoregulation]
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{{Carbohydrate metabolism}}
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{{Glycogenolysis}}
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{{Gluconeogenesis}}
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{{Fructose and galactose metabolism}}
   
 
[[Category:Metabolism]]
 
[[Category:Metabolism]]
   
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{{enWP|Carbohydrate metabolism}}
 
{{enWP|Carbohydrate metabolism}}

Revision as of 20:32, January 12, 2008

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Carbohydrate metabolism denotes the various biochemical processes responsible for the formation, breakdown and interconversion of carbohydrates in living organisms.

The most important carbohydrate is glucose, a simple sugar (monosaccharide) that is metabolized by nearly all known organisms. Glucose and other carbohydrates are part of a wide variety of metabolic pathways across species: plants synthesize carbohydrates from atmospheric gases by photosynthesis, which can then be consumed by other organisms and used as fuel for cellular respiration. Oxidation of one gram of carbohydrate yields approximately 4 kcal of energy. Energy obtained from carbohydrate metabolism is usually stored in the form of ATP. Organisms capable of aerobic respiration metabolize glucose and oxygen to release energy with carbon dioxide and water as byproducts.

All carbohydrates share a general formula of approximately CnH2nOn; glucose is C6H12O6. Monosaccharides may be chemically bonded together to form disaccharides such as sucrose and longer polysaccharides such as starch and cellulose.

Carbohydrates are a superior short-term energy reserve for organisms, because they are much simpler to metabolize than fats or proteins. In animals, all dietary carbohydrates are delivered to cells in the form of glucose. Carbohydrates are typically stored as long polymers of glucose molecules with Glycosidic bonds for structural support (e.g. chitin, cellulose) or energy storage (e.g. glycogen, starch). However, the strong affinity of carbohydrates for water makes storage of large quantities of carbohydrates inefficient due to the large molecular weight of the solvated water-carbohydrate complex. In some organisms, excess carbohydrates are catabolised to form Acetyl-CoA, where they enter the fatty acid synthesis pathway. Fatty acids, triglycerides, and other lipids are commonly used for long-term energy storage. The hydrophobic character of lipids makes them a much more compact form of energy storage than hydrophilic carbohydrates.

Catabolism

Main article: Carbohydrate catabolism

Oligo/polysaccharides are cleaved first to smaller monosaccharides by enzymes called Glycoside hydrolases. The monosaccharide units can then enter into monosaccharide catabolism.

Metabolic pathways

Glucoregulation

Glucoregulation is the maintenance of steady levels of glucose in the body; it is part of homeostasis, and keeps a constant internal environment around cells in the body.

The hormone insulin makes the body convert glucose into glycogen and puts it into the liver; the insulin is made in the pancreas, and is secreted when the blood sugar is too high. Insulin also promotes the use of glucose by the muscles.

The hormone glucagon, on the other hand, acts in the opposite direction and promotes the conversion of glycogen to glucose in response to low blood sugar.

Human diseases of carbohydrate metabolism

See also


External links

Template:Carbohydrate metabolism Template:Glycogenolysis Template:Gluconeogenesis Template:Fructose and galactose metabolism

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