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Encyclopedia > Glycogen
Glycogen Structure Segment
Glycogen Structure Segment

Glycogen is a polysaccharide of glucose (Glc) which functions as the primary short term energy storage in animal cells. It is made primarily by the liver and the muscles, but can also be made by the brain, uterus, and the vagina.[1] Glycogen is the analogue of starch, a less branched glucose polymer in plants, and is commonly referred to as animal starch, having a similar structure to amylopectin. Glycogen is found in the form of granules in the cytosol in many cell types, and plays an important role in the glucose cycle. Glycogen forms an energy reserve that can be quickly mobilized to meet a sudden need for glucose, but one that is less compact than the energy reserves of triglycerides (fat). In the liver hepatocytes, glycogen can compose up to 8% of the fresh weight (100–120 g in an adult) soon after a meal.[citation needed] Only the glycogen stored in the liver can be made accessible to other organs. In the muscles, glycogen is found in a much lower concentration (1% of the muscle mass), but the total amount exceeds that in liver. Small amounts of glycogen are found in the kidneys, and even smaller amounts in certain glial cells in the brain and white blood cells. The uterus also stores glycogen during pregnancy to nourish the embryo. Image File history File links Glykogen. ... Image File history File links Glykogen. ... Polysaccharides (sometimes called glycans) are relatively complex carbohydrates. ... Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ... For other uses, see Animal (disambiguation). ... For the bird, see Liver bird. ... For other uses of Muscles, see Muscles (disambiguation). ... The human brain In animals, the brain (enkephale) (Greek for in the skull), is the control center of the central nervous system, responsible for behavior. ... This article is about female reproductive anatomy. ... The vagina, (from Latin, literally sheath or scabbard ) is the tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. ... Starch (CAS# 9005-25-8, chemical formula (C6H10O5)n,[1]) is a mixture of amylose and amylopectin (usually in 20:80 or 30:70 ratios). ... For other uses, see Plant (disambiguation). ... Amylopectin is a highly branched polymer of glucose found in plants. ... The cytosol (cf. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... This is a description of the glucose cycle, presented in clear and simple words that everyone can understand. ... Triglyceride (blue: fatty acid; red: glycerol backbone) Triglycerides are glycerides in which the glycerol is esterified with three fatty acids. ... Sinusoid of a rat liver with fenestrated endothelial cells. ... For other uses of Muscles, see Muscles (disambiguation). ... The kidneys are the organs that filter wastes (such as urea) from the blood and excrete them, along with water, as urine. ... Neuroglia cells of the brain shown by Golgis method. ... The human brain In animals, the brain (enkephale) (Greek for in the skull), is the control center of the central nervous system, responsible for behavior. ... White Blood Cells is also the name of a White Stripes album. ...



== poop! ==

Contents

Function and regulation of liver glycogen

As a carbohydrate meal is eaten and digested, blood glucose levels rise, and the pancreas secretes insulin. Glucose from the portal vein enters the liver cells (hepatocytes). Insulin acts on the hepatocytes to stimulate the action of several enzymes, including glycogen synthase. Glucose molecules are added to the chains of glycogen as long as both insulin and glucose remain plentiful. In this postprandial or "fed" state, the liver takes in more glucose from the blood than it releases. Lactose is a disaccharide found in milk. ... In medicine, blood sugar is glucose in the blood. ... The pancreas is a gland organ in the digestive and endocrine systems of vertebrates. ... Not to be confused with inulin. ... The portal vein is a major vein in the human body draining blood from the digestive system and its associated glands. ... For the bird, see Liver bird. ... Sinusoid of a rat liver with fenestrated endothelial cells. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Glycogen synthase (UDP-glucose-glycogen glucosyltransferase) is a glycosyltransferase enzyme (EC number 2. ... Look up Postprandial in Wiktionary, the free dictionary. ...


After a meal has been digested and glucose levels begin to fall, insulin secretion is reduced, and glycogen synthesis stops. About four hours after a meal[citation needed], glycogen begins to be broken down to be converted again to glucose. Glycogen phosphorylase is the primary enzyme of glycogen breakdown. For the next 8–12 hours, glucose derived from liver glycogen will be the primary source of blood glucose to be used by the rest of the body for fuel. For the industrial process, see anaerobic digestion. ...


Glucagon is another hormone produced by the pancreas, which in many respects serves as a counter-signal to insulin. When the blood sugar begins to fall below normal, glucagon is secreted in increasing amounts. It stimulates glycogen breakdown into glucose even when insulin levels are abnormally high. Glucagon ball and stick model A microscopic image stained for glucagon. ...


In muscle and other cells

Muscle cell glycogen appears to function as an immediate reserve source of available glucose for muscle cells. Other cells that contain small amounts use it locally as well. Muscle cells lack the ability to pass glucose into the blood, so the glycogen they store internally is destined for internal use and is not shared with other cells, unlike liver cells.


Glycogen debt and endurance exercise

Due to the body's inability to hold more than around 2,000 kcal of glycogen,[citation needed] long-distance athletes such as marathon runners, cross-country skiers, and cyclists go into glycogen debt, where almost all of the athlete's glycogen stores are depleted after long periods of exertion without enough energy consumption. This phenomenon is referred to as "hitting the wall" or "bonking". In marathon runners it normally happens around the 20 mile (32 km) point of a marathon, where around 100 kcal are spent per mile,[citation needed] depending on the size of the runner and the race course. However, it can be delayed by a carbohydrate loading before the task. Etymology: French calorie, from Latin calor (heat), from calere (to be warm). ... Modern day marathon runners The word marathon refers to a long-distance road running event of 42. ... Cross-Country trails are often less crowded than Alpine ski slopes. ... A cyclist is a person who engages in cycling whether as a sport or rides a bicycle for recreation or transportation. ... In sports, carbohydrate loading, also known as carbo-loading, is a strategy employed by endurance athletes such as marathon runners to maximize the storage of glycogen in the muscles. ...


When experiencing glycogen debt, athletes often experience extreme fatigue to the point that it is difficult to move. The word fatigue is used in everyday living to describe a range of afflictions, varying from a general state of lethargy to a specific work induced burning sensation within muscle. ...


Disorders of glycogen metabolism

The most common disease in which glycogen metabolism becomes abnormal is diabetes, in which, because of abnormal amounts of insulin, liver glycogen can be abnormally accumulated or depleted. Restoration of normal glucose metabolism usually normalizes glycogen metabolism as well. Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... This article is about the disease that features high blood sugar. ...


In hypoglycemia caused by excessive insulin, liver glycogen levels are high, but the high insulin level prevents the glycogenolysis necessary to maintain normal blood sugar levels. Glucagon is a common treatment for this type of hypoglycemia. Hypoglycemia (hypoglycaemia in British English) is a medical term referring to a pathologic state produced by a lower than normal level of glucose (sugar) in the blood. ... Glycogen Glucose Glucose-6-phosphate Glycogenolysis is the catabolism of glycogen by removal of a glucose monomer and addition of phosphate to produce glucose-1-phosphate. ... Glucagon ball and stick model A microscopic image stained for glucagon. ...


Various inborn errors of metabolism are caused by deficiencies of enzymes necessary for glycogen synthesis or breakdown. These are collectively referred to as glycogen storage diseases. Inborn errors of metabolism comprise a large class of genetic diseases involving disorders of metabolism. ... Glycogen storage disease is any one of several inborn errors of metabolism that result from enzyme defects that affect the processing of glycogen synthesis or breakdown within muscles, liver, and other cell types. ...


Synthesis

Main article: Glycogenesis

Glycogen synthesis differs from glycogen breakdown. Unlike breakdown, synthesis is endergonic, meaning that glycogen is not synthesized without the input of energy. Energy for glycogen synthesis comes from UTP, which reacts with glucose-1-phosphate, forming UDP-glucose, in reaction catalysed by UDP-glucosediphosphorylase. Glycogen is synthesized from monomers of UDP-glucose by the enzyme Glycogen synthase, which progressively lengthens the glycogen chain. As glycogen synthase can only lengthen an existing chain, the protein glycogenin is needed to initiate the synthesis of glycogen. Glycogenesis is the process of glycogen synthesis, in which glucose molecules are added to chains of glycogen. ... Endergonic means absorbing energy in the form of work. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide primarily known in biochemistry as the molecular currency of intracellular energy transfer. ... Glucose 1-phosphate is a glucose molecule with a phosphate group on the 1-carbon. ... Uridine diphosphate glucose (uracil-diphosphate glucose, UDP-glucose) is a nucleotide. ... Uridine diphosphate glucose (uracil-diphosphate glucose, UDP-glucose) is a nucleotide. ... Glycogen synthase (UDP-glucose-glycogen glucosyltransferase) is a glycosyltransferase enzyme (EC number 2. ... Glycogenin is an enzyme involved in the initiation of glycogen biosynthesis. ...


Breakdown

Main article: Glycogenolysis

Glycogen is cleaved from the nonreducing ends of the chain by the enzyme glycogen phosphorylase to produce monomers of glucose-1-phosphate that is then converted to Glucose 6-phosphate. A special debranching enzyme is needed to remove the alpha(1-6) branches in branched glycogen and reshape the chain into linear polymer. The G6P monomers produced have three possible fates: Glycogen Glucose Glucose-6-phosphate Glycogenolysis is the catabolism of glycogen by removal of a glucose monomer and addition of phosphate to produce glucose-1-phosphate. ... Glycogen phosphorylase is the enzyme necessary to break up glycogen into glucose subunits. ... Glucose-6-phosphate (G6P) is a phosphorylated glucose molecule on carbon 6. ... A debranching enzyme is a molecule that helps facilitate the breakdown of glycogen. ...

  • G6P can continue on the glycolysis pathway and be used as fuel.
  • G6P can enter the pentose phosphate pathway via the enzyme Glucose-6-phosphate dehydrogenase to produce NADPH and 5-carbon sugars.
  • In the liver and kidney, G6P can be dephosphorylated back to Glucose by the enzyme Glucose 6-phosphatase. This is the final step in the gluconeogenesis pathway.

The word glycolysis is derived from Greek γλυκύς (sweet) and λύσις (letting loose). ... The pentose phosphate pathways Nonoxidative phase The pentose phosphate pathway (also called Phosphogluconate Pathway, or Hexose Monophosphate Shunt [HMP shunt]) is a process that serves to generate NADPH and the synthesis of pentose (5-carbon) sugars. ... RNA expression pattern Orthologs Human Mouse Entrez Ensembl Uniprot Refseq Location Pubmed search Glucose-6-phosphate dehydrogenase (G6PD) is an enzyme in the pentose phosphate pathway (see image), a metabolic pathway that supplies reducing energy to cells (most notably erythrocytes) by maintaining the level of the co-enzyme nicotinamide adenine... Glucose 6-phosphatase is an enzyme in the glycogenolysis pathway that removes the phosphate from glucose 6-phosphate. ... Pyruvic acid Oxaloacetic acid Phosphoenolpyruvate Fructose 1,6-bisphosphate Fructose 6-phosphate Glucose-6-phosphate Glucose Gluconeogenesis is the generation of glucose from non-sugar carbon substrates like pyruvate, lactate, glycerol, and amino acids (primarily alanine and glutamine). ...

References

  1. ^ Anatomy and Physiology. Saladin, Kenneth S. McGraw-Hill, 2007.

See also

Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of eubacteria. ...

External links


  Results from FactBites:
 
Glycogen - Wikipedia, the free encyclopedia (1029 words)
Glycogen (commonly known as animal starch although this name is inaccurate) is a polysaccharide that is the principal storage form of glucose (Glc) in animal and human cells.
Glycogenin is a glycosyltransferase and occurs as a dimer in the core of glycogen.
Glycogen phosphorylase is the primary enzyme of glycogen breakdown.
glycogen - HighBeam Encyclopedia (342 words)
glycogen, starchlike polysaccharide (see carbohydrate) that is found in the liver and muscles of humans and the higher animals and in the cells of the lower animals.
Glycogen is formed by the liver from glucose in the bloodstream and is stored in the liver; conversion of glucose to glycogen (glycogenesis) and hydrolysis of glycogen to glucose (glycogenolysis) together are the usual mechanism for maintenance of normal levels of blood sugar.
Glycogen is also produced by and stored in muscle cells; during short periods of strenuous activity, energy is released in the muscles by direct conversion of glycogen to lactic acid.
  More results at FactBites »

 
 

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