Glycogen is a polysaccharide of glucose (Glc) which functions as the primary short term energy storage in animal cells. Polysaccharides are relatively complex Carbohydrates They are Polymers made up of many Monosaccharides joined together by Glycosidic bonds Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. It is made primarily by the liver and the muscles, but can also be made by the brain, uterus, and the vagina. The liver is a vital organ in the human body and is present in Vertebrates and some other animals Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain The uterus (from the Latin word for womb) is the major Female reproductive organ of most Mammals including Humans One end the The vagina (from Latin, literally " Sheath " or " Scabbard " is a fibromuscular tubular tract leading from the Uterus [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. Starch, CAS # 9005-25-8 Chemical formula (C6H10O5n is a Polysaccharide Plants are living Organisms belonging to the kingdom Plantae. Amylopectin ( CAS # 9037-22-3 is a highly branched Polymer of Glucose found in plants Glycogen is found in the form of granules in the cytosol in many cell types, and plays an important role in the glucose cycle. The cytosol or intracellular fluid (or cytoplasmic matrix) is the liquid found inside cells. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called The glucose cycle (also known as the hepatic futile cycle occurs primarily in the Liver and is the dynamic equilibrium between Glucose and Glucose 6-phosphate 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 Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός (more properly known as, TAG or triacylglyceride) is Glyceride in which the Glycerol is Esterified with three Fatty acids It is the In the liver hepatocytes, glycogen can compose up to 8% of the fresh weight (100–120 g in an adult) soon after a meal. Hepatocytes make up 70-80% of the Cytoplasmic mass of the Liver. 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. Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the 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 kidneys are complicated organs that have numerous biological roles Glial cells, commonly called neuroglia or simply glia (Greek for "glue" are non- Neuronal cells that provide support and nutrition The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain The uterus also stores glycogen during pregnancy to nourish the embryo.
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Structure and biochemistry
Glycogen is a highly branched polymer that is better described as a dendrimer of about 60,000 glucose residues and has a molecular weight between 106 and 107 daltons (~4. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds Dendrimers are repeatedly branched Molecules The huge number of papers on dendritic architectures such as dendrimers dendronized hyperbranched and brush-polymers has generated The unified atomic mass unit ( u) or Dalton ( Da) or sometimes universal mass unit, is an unit of Mass used to express 8 million). Most of Glc units are linked by α-1,4 glycosidic bonds, approximately 1 in 12 Glc residues also makes -1,6 glycosidic bond with a second Glc, which results in the creation of a branch. In Chemistry, a glycosidic bond is a certain type of Functional group that joins a Carbohydrate (sugar molecule to another which may be another carbohydrate Glycogen does not possess a reducing end: the 'reducing end' glucose residue is not free but is covalently bound to a protein termed glycogenin as a beta-linkage to a surface tyrosine residue. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state A reducing sugar is any sugar that in basic solution forms some Aldehyde or Ketone. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Glycogenin is an Enzyme involved in Glycogen Biosynthesis. This enzyme was discovered by Dr In Chemistry, a glycosidic bond is a certain type of Functional group that joins a Carbohydrate (sugar molecule to another which may be another carbohydrate Glycogenin is a glycosyltransferase and occurs as a dimer in the core of glycogen. Glycogenin is an Enzyme involved in Glycogen Biosynthesis. This enzyme was discovered by Dr The glycogen granules contain both glycogen and the enzymes of glycogen synthesis (glycogenesis) and degradation (glycogenolysis). Glycogenesis is the process of Glycogen synthesis in which Glucose molecules are added to chains of glycogen Glycogenolysis (also known as "Glycogenlysis" is the Catabolism of Glycogen by removal of a Glucose monomer through cleavage with inorganic The enzymes are nested between the outer branches of the glycogen molecules and act on the non-reducing ends. Therefore, the many non-reducing end-branches of glycogen facilitate its rapid synthesis and catabolism. For the related metabolic process see Anabolism. Catabolism is the set of Metabolic pathways which break down molecules into
Function and regulation of liver glycogen
As a meal containing carbohydrates is eaten and digested, blood glucose levels rise, and the pancreas secretes insulin. Carbohydrates (from ' Hydrates of Carbon ' or saccharides ( Greek σάκχαρον meaning " Sugar " are the most Blood sugar, used in a physiological context is a misnomer and misleading The pancreas is a Gland organ in the digestive and Endocrine system of Vertebrates. Insulin is a Hormone with intensive effects on both metabolism and several other body systems (eg vascular compliance Glucose from the portal vein enters the liver cells (hepatocytes). The liver is a vital organ in the human body and is present in Vertebrates and some other animals Hepatocytes make up 70-80% of the Cytoplasmic mass of the Liver. Insulin acts on the hepatocytes to stimulate the action of several enzymes, including glycogen synthase. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Glycogen synthase ( UDP-glucose-glycogen glucosyltransferase') is a Glycosyltransferase Enzyme ( EC number 2 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. Postprandial means after eating a meal This term is often used in the context of blood sugar (or blood Glucose) levels which are normally measured 2 hours after eating
After a meal has been digested and glucose levels begin to fall, insulin secretion is reduced, and glycogen synthesis stops. Digestion is the breaking down of chemicals in the body into a form that can be absorbed About four hours after a meal, glycogen begins to be broken down and converted again to glucose. Glycogen phosphorylase is the primary enzyme of glycogen breakdown. Glycogen phosphorylase is one of the Phosphorylase Enzymes ( It breaks up Glycogen into Glucose Subunits. 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.
Glucagon is another hormone produced by the pancreas, which in many respects serves as a counter-signal to insulin. Glucagon is an important Hormone involved in Carbohydrate metabolism. When the blood sugar begins to fall below normal, glucagon is secreted in increasing amounts. Blood sugar, used in a physiological context is a misnomer and misleading It stimulates glycogen breakdown into glucose even when insulin levels are abnormally high.
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 glucose-6-phosphatase enzyme, so they 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, 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 article is about the unit of energy For its use in Nutrition and Food labelling regulations, see the article on Food energy. The marathon is a long-distance foot race with an official distance of 42 Cross-country skiing (also known as XC skiing) is a Winter sport popular in many countries with large snowfields primarily Northern Europe, Cycling is the use of Bicycles or - less commonly - Unicycles Tricycles Quadricycles and other similar wheeled Human powered vehicles 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, depending on the size of the runner and the race course. However, it can be delayed by a carbohydrate loading before the task. In sports carbohydrate loading, colloquially known as carbo-loading, is a strategy employed by endurance athletes such as marathon runners to maximize the storage
When experiencing glycogen debt, athletes often experience extreme fatigue to the point that it is difficult to move.
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. Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. Diabetes mellitus (ˌdaɪəˈbiːtiːz or /ˌdaɪəˈbiːtəs/ /məˈlaɪtəs/ or /ˈmɛlətəs/ often referred to simply as diabetes ( Ancient Greek: grc Restoration of normal glucose metabolism usually normalizes glycogen metabolism as well.
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. Hypoglycemia or hypoglycaemia is the medical term for a pathologic state produced by a lower than normal level of Glucose ( sugar) in the blood Glycogenolysis (also known as "Glycogenlysis" is the Catabolism of Glycogen by removal of a Glucose monomer through cleavage with inorganic Glucagon is a common treatment for this type of hypoglycemia. Glucagon is an important Hormone involved in Carbohydrate metabolism.
Various inborn errors of metabolism are caused by deficiencies of enzymes necessary for glycogen synthesis or breakdown. Inborn errors of metabolism comprise a large class of genetic Diseases involving disorders of Metabolism. These are collectively referred to as glycogen storage diseases. Glycogen storage disease (synonyms glycogenosis, dextrinosis) is any one of several inborn errors of metabolism that result from Enzyme defects
Synthesis
Glycogen synthesis differs from glycogen breakdown. Glycogenesis is the process of Glycogen synthesis in which Glucose molecules are added to chains of glycogen Unlike breakdown, synthesis is endergonic, meaning that glycogen is not synthesized without the input of energy. Endergonic means absorbing energy in the form of work Its etymology stems from the suffix -ergonic as derived from the Greek root ergon meaning work, Energy for glycogen synthesis comes from UTP, which reacts with glucose-1-phosphate, forming UDP-glucose, in reaction catalysed by UDP-glucose pyrophosphorylase. Uridine triphosphate is a Pyrimidine Nucleotide, consisting of the Organic base Uracil linked to the 1' carbon atom of the sugar Ribose Glucose 1-phosphate (also called cori ester) is a Glucose molecule with a Phosphate group on the 1'-carbon Uridine diphosphate glucose ( uracil-diphosphate glucose, UDP-glucose) is a Nucleotide sugar. UDP-glucose pyrophosphorylase (or UTP-glucose-1-phosphate uridylyltransferase) is an enzyme associated with Glycogenesis. Glycogen is synthesized from monomers of UDP-glucose by the enzyme Glycogen synthase, which progressively lengthens the glycogen chain. Uridine diphosphate glucose ( uracil-diphosphate glucose, UDP-glucose) is a Nucleotide sugar. Glycogen synthase ( UDP-glucose-glycogen glucosyltransferase') is a Glycosyltransferase Enzyme ( EC number 2 As glycogen synthase can only lengthen an existing chain, the protein glycogenin is needed to initiate the synthesis of glycogen. Glycogenin is an Enzyme involved in Glycogen Biosynthesis. This enzyme was discovered by Dr
Breakdown
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. Glycogenolysis (also known as "Glycogenlysis" is the Catabolism of Glycogen by removal of a Glucose monomer through cleavage with inorganic Glycogen phosphorylase is one of the Phosphorylase Enzymes ( It breaks up Glycogen into Glucose Subunits. Glucose 6-phosphate (also known as Robison ester) is Glucose sugar Phosphorylated on carbon 6 A special debranching enzyme is needed to remove the alpha(1-6) branches in branched glycogen and reshape the chain into linear polymer. A debranching enzyme is a molecule that helps facilitate the breakdown of Glycogen. The G6P monomers produced have three possible fates:
- G6P can continue on the glycolysis pathway and be used as fuel. See also Gluconeogenesis, which carries out a process wherein glucose is synthesized rather than catabolized
- G6P can enter the pentose phosphate pathway via the enzyme Glucose-6-phosphate dehydrogenase to produce NADPH and 5-carbon sugars. The pentose phosphate pathway (also called Phosphogluconate Pathway or HexoseMonophosphate Shunt shunt is a process that serves to generate NADPH and the synthesis of pentose Glucose-6-phosphate dehydrogenase ( G6PD) is a cytosolic Enzyme in the Pentose phosphate pathway (see image a Metabolic pathway that supplies
- In the liver and kidney, G6P can be dephosphorylated back to Glucose by the enzyme Glucose 6-phosphatase. Glucose 6-phosphatase (Glc-6-Pase is an Enzyme that hydrolyzes Glucose-6-phosphate resulting in the creation of a phosphate group and free glucose This is the final step in the gluconeogenesis pathway. Gluconeogenesis (abreviated GNG) is a Metabolic pathway that results in the generation of Glucose from non- Carbohydrate carbon substrates such
References
- ^ Anatomy and Physiology. Saladin, Kenneth S. McGraw-Hill, 2007.
See also
External links
Not to be confused with Glycoprotein. Peptidoglycan, also known as murein, is a Polymer consisting of sugars and amino Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and booksDictionary
glycogen
-noun
- (biochemistry) A polysaccharide that is the main form of carbohydrate storage in animals; converted to glucose as needed.
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