Carbohydrate metabolism 383675 217523999 2008-06-06T12:40:27Z Arcadian 104523 nav '''Carbohydrate metabolism''' denotes the various [[biochemistry|biochemical]] processes responsible for the [[anabolism|formation]], [[catabolism|breakdown]] and interconversion of [[carbohydrates]] in [[life|living]] [[organism]]s. 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. 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]]. Carbohydrates are a superior short-term energy reserve for organisms, because they are much simpler to metabolize than [[fat]]s 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. ==Catabolism== {{Main|Carbohydrate catabolism}} Oligo/polysaccharides are cleaved first to smaller monosaccharides by enzymes called [[Glycoside hydrolase]]s. The monosaccharide units can then enter into monosaccharide catabolism ==Metabolic pathways== * [[Carbon fixation]], whereby CO<sub>2</sub> is reduced to carbohydrate. * [[Glycolysis]] - the breakdown of the [[glucose]] molecule in order to obtain [[adenosine triphosphate|ATP]] and [[Pyruvate]] ** Pyruvate from glycolysis enters the [[Krebs cycle]] in [[aerobic]] organisms. * The [[Pentose phosphate pathway]], which acts in the conversion of [[hexose]]s into [[pentose]]s and in [[NADPH]] regeneration. * [[Glycogenesis]] - the conversion of excess glucose into [[glycogen]] in order to prevent excessive [[osmotic pressure]] buildup inside the cell * [[Glycogenolysis]] - the breakdown of glycogen into glucose, in order to provide a steady level of glucose supply for glucose-dependent tissues. * [[Gluconeogenesis]] - ''de novo'' synthesis of glucose molecules from simple [[organic chemistry|organic]] compounds ==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== * [[Diabetes mellitus]] * [[Lactose intolerance]] * [[Fructose intolerance]] * [[Galactosemia]] * [[Glycogen storage disease]] ==External links== * {{MeshName|Carbohydrate+metabolism}} *[http://diabetescorner.blogspot.com/2007/09/glucose-metabolism.html Glucose Metabolism and Diabetes] *[http://www.bbc.co.uk/schools/gcsebitesize/biology/humansasorganisms/6homeostasisrev4.shtml BBC - GCSE Bitesize - Biology | Humans | Glucoregulation] {{Carbohydrate metabolism}} {{Glycogenolysis}} {{Gluconeogenesis}} {{Fructose and galactose metabolism}} {{Glycosaminoglycan metabolism enzymes}} {{Glycoprotein metabolism enzymes}} [[Category:Metabolism]] [[de:Glucose-Stoffwechsel]] [[fr:Métabolisme des glucides]] [[ja:炭水化物代謝]] [[th:การเผาผลาญคาร์โบไฮเดรต]]