Glucose is a simple sugar with the molecular formula . Glucose is the most abundant monosaccharide, a subcategory of . Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using energy from sunlight, where it is used to make cellulose in , the most abundant carbohydrate in the world.
In energy metabolism, glucose is the most important source of energy in all . Glucose for metabolism is stored as a polymer, in plants mainly as starch and amylopectin, and in animals as glycogen. Glucose circulates in the blood of animals as blood sugar. The naturally occurring form of glucose is -glucose, while L-glucose is produced synthetically in comparatively small amounts and is less biologically active. Glucose is a monosaccharide containing six carbon atoms and an aldehyde group, and is therefore an aldohexose. The glucose molecule can exist in an open-chain (acyclic) as well as ring (cyclic) form. Glucose is naturally occurring and is found in its free state in fruits and other parts of plants. In animals, glucose is released from the breakdown of glycogen in a process known as glycogenolysis.
Glucose, as intravenous sugar solution, is on the World Health Organization's List of Essential Medicines. It is also on the list in combination with sodium chloride.
The name glucose is derived from Ancient Greek γλεῦκος (, "wine, must"), from γλυκύς (, "sweet").Thénard, Gay-Lussac, Biot, and Dumas (1838) "Rapport sur un mémoire de M. Péligiot, intitulé: Recherches sur la nature et les propriétés chimiques des sucres". (Report on a memoir of Mr. Péligiot, titled: Investigations on the nature and chemical properties of sugars), Comptes rendus, 7 : 106–113. From page 109. : "Il résulte des comparaisons faites par M. Péligot, que le sucre de raisin, celui d'amidon, celui de diabètes et celui de miel ont parfaitement la même composition et les mêmes propriétés, et constituent un seul corps que nous proposons d'appeler (1). ... (1) γλευχος, moût, vin doux." It follows from the comparisons made by Mr. Péligot, that the sugar from grapes, that from starch, that from diabetes and that from honey have exactly the same composition and the same properties, and constitute a single substance that we propose to call glucose (1) ... (1) γλευχος, must, sweet wine. The suffix "-ose" is a chemical classifier, denoting a sugar.
Since glucose is a basic necessity of many organisms, a correct understanding of its chemical makeup and structure contributed greatly to a general advancement in organic chemistry. This understanding occurred largely as a result of the investigations of Emil Fischer, a German chemist who received the 1902 Nobel Prize in Chemistry for his findings. The synthesis of glucose established the structure of organic material and consequently formed the first definitive validation of Jacobus Henricus van 't Hoff's theories of chemical kinetics and the arrangements of chemical bonds in carbon-bearing molecules. Between 1891 and 1894, Fischer established the stereochemical configuration of all the known sugars and correctly predicted the possible , applying Van 't Hoff's theory of asymmetrical carbon atoms. The names initially referred to the natural substances. Their enantiomers were given the same name with the introduction of systematic nomenclatures, taking into account absolute stereochemistry (e.g. Fischer nomenclature, / nomenclature).
For the discovery of the metabolism of glucose Otto Meyerhof received the Nobel Prize in Physiology or Medicine in 1922. "Otto Meyerhof - Facts - NobelPrize.org" . NobelPrize.org. Retrieved on 5 September 2018. Hans von Euler-Chelpin was awarded the Nobel Prize in Chemistry along with Arthur Harden in 1929 for their "research on the fermentation of sugar and their share of enzymes in this process". "Hans von Euler-Chelpin - Facts - NobelPrize.org" . NobelPrize.org. Retrieved on 5 September 2018. "Arthur Harden - Facts - NobelPrize.org" . NobelPrize.org. Retrieved on 5 September 2018. In 1947, Bernardo Houssay (for his discovery of the role of the pituitary gland in the metabolism of glucose and the derived carbohydrates) as well as Carl Cori and Gerty Cori (for their discovery of the conversion of glycogen from glucose) received the Nobel Prize in Physiology or Medicine. "Bernardo Houssay - Facts - NobelPrize.org" . NobelPrize.org. Retrieved on 5 September 2018. "Carl Cori - Facts - NobelPrize.org" . NobelPrize.org. Retrieved on 5 September 2018. "Gerty Cori - Facts - NobelPrize.org" . NobelPrize.org. Retrieved on 5 September 2018. In 1970, Luis Leloir was awarded the Nobel Prize in Chemistry for the discovery of glucose-derived sugar nucleotides in the biosynthesis of carbohydrates. "Luis Leloir - Facts - NobelPrize.org" . NobelPrize.org. Retrieved on 5 September 2018.
With six carbon atoms, it is classed as a hexose, a subcategory of the . -Glucose is one of the sixteen aldohexose . The -isomer, -glucose, also known as dextrose, occurs widely in nature, but the -isomer, L-glucose, does not. Glucose can be obtained by hydrolysis of carbohydrates such as milk sugar (lactose), cane sugar (sucrose), maltose, cellulose, glycogen, etc. Dextrose is commonly commercially manufactured from cornstarch in the US and Japan, from potato and wheat starch in Europe, and from tapioca starch in tropical areas. The manufacturing process uses hydrolysis via pressurized steaming at controlled pH in a jet followed by further enzymatic depolymerization."glucose." The Columbia Encyclopedia, 6th ed.. 2015. Encyclopedia.com. 17 Nov. 2015 http://www.encyclopedia.com . Unbonded glucose is one of the main ingredients of honey.
α--glucofuranose | β--glucofuranose | |
α--glucopyranose | β--glucopyranose | |
The reaction between C-1 and C-5 yields a six-membered heterocycle system called a pyranose, which is a monosaccharide sugar (hence "-ose") containing a derivatised pyran skeleton. The (much rarer) reaction between C-1 and C-4 yields a five-membered furanose ring, named after the cyclic ether furan. In either case, each carbon in the ring has one hydrogen and one hydroxyl attached, except for the last carbon (C-4 or C-5) where the hydroxyl is replaced by the remainder of the open molecule (which is or respectively).
The ring-closing reaction can give two products, denoted "α-" and "β-". When a glucopyranose molecule is drawn in the Haworth projection, the designation "α-" means that the hydroxyl group attached to C-1 and the group at C-5 lies on opposite sides of the ring's plane (a trans arrangement), while "β-" means that they are on the same side of the plane (a cis arrangement). Therefore, the open-chain isomer -glucose gives rise to four distinct cyclic isomers: α--glucopyranose, β--glucopyranose, α--glucofuranose, and β--glucofuranose. These five structures exist in equilibrium and interconvert, and the interconversion is much more rapid with acid catalysis.
The other open-chain isomer -glucose similarly gives rise to four distinct cyclic forms of -glucose, each the mirror image of the corresponding -glucose.
The glucopyranose ring (α or β) can assume several non-planar shapes, analogous to the "chair" and "boat" conformations of cyclohexane. Similarly, the glucofuranose ring may assume several shapes, analogous to the "envelope" conformations of cyclopentane.
In the solid state, only the glucopyranose forms are observed.
Some derivatives of glucofuranose, such as 1,2- O-isopropylidene--glucofuranose are stable and can be obtained pure as crystalline solids. For example, reaction of α-D-glucose with para-tolylboronic acid reforms the normal pyranose ring to yield the 4-fold ester α-D-glucofuranose-1,2:3,5-bis( p-tolylboronate).
The open-chain form is thermodynamically unstable, and it spontaneously to the cyclic forms. (Although the ring closure reaction could in theory create four- or three-atom rings, these would be highly strained, and are not observed in practice.) In solutions at room temperature, the four cyclic isomers interconvert over a time scale of hours, in a process called mutarotation.. Starting from any proportions, the mixture converges to a stable ratio of α:β 36:64. The ratio would be α:β 11:89 if it were not for the influence of the anomeric effect. Mutarotation is considerably slower at temperatures close to .
Note that the - prefix does not refer directly to the optical properties of the compound. It indicates that the C-5 chiral centre has the same handedness as that of -glyceraldehyde (which was so labelled because it is dextrorotatory). The fact that -glucose is dextrorotatory is a combined effect of its four chiral centres, not just of C-5; and indeed some of the other -aldohexoses are levorotatory.
The conversion between the two anomers can be observed in a polarimeter since pure α-glucose has a specific rotation angle of +112.2°·ml/(dm·g), pure β- D- glucose of +17.5°·ml/(dm·g).Manfred Hesse, Herbert Meier, Bernd Zeeh, Stefan Bienz, Laurent Bigler, Thomas Fox: Spektroskopische Methoden in der organischen Chemie. 8th revised Edition. Georg Thieme, 2011, , p. 34 (in German). When equilibrium has been reached after a certain time due to mutarotation, the angle of rotation is +52.7°·ml/(dm·g). By adding acid or base, this transformation is much accelerated. The equilibration takes place via the open-chain aldehyde form.
Glucose is produced by plants through the photosynthesis using sunlight, water and carbon dioxide and can be used by all living organisms as an energy and carbon source. However, most glucose does not occur in its free form, but in the form of its polymers, i.e. lactose, sucrose, starch and others which are energy reserve substances, and cellulose and chitin, which are components of the cell wall in plants or fungi and , respectively. These polymers, when consumed by animals, fungi and bacteria, are degraded to glucose using enzymes. All animals are also able to produce glucose themselves from certain precursors as the need arises. , cells of the renal medulla and erythrocytes depend on glucose for their energy production.Peter C. Heinrich: Löffler/Petrides Biochemie und Pathobiochemie. Springer-Verlag, 2014, , p. 195. (german) In adult humans, there is about of glucose,U. Satyanarayana: Biochemistry. Elsevier Health Sciences, 2014, . p. 674. of which about is present in the blood. Approximately of glucose is produced in the liver of an adult in 24 hours.
Many of the long-term complications of diabetes (e.g., blindness, kidney failure, and peripheral neuropathy) are probably due to the glycation of proteins or . In contrast, enzyme-regulated addition of sugars to protein is called glycosylation and is essential for the function of many proteins.
In order to get into or out of cell membranes of cells and membranes of cell compartments, glucose requires special transport proteins from the major facilitator superfamily. In the small intestine (more precisely, in the jejunum),Harold A. Harper: Medizinische Biochemie. Springer-Verlag, 2013, , p. 641. glucose is taken up into the intestinal epithelium with the help of glucose transporters via a secondary active transport mechanism called sodium ion-glucose symport via sodium/glucose cotransporter 1 (SGLT1). Further transfer occurs on the basolateral side of the intestinal epithelial cells via the glucose transporter GLUT2, as well uptake into hepatocyte, kidney cells, cells of the islets of Langerhans, , , and . Glucose enters the liver via the portal vein and is stored there as a cellular glycogen. In the liver cell, it is Phosphorylation by glucokinase at position 6 to form glucose 6-phosphate, which cannot leave the cell. Glucose 6-phosphatase can convert glucose 6-phosphate back into glucose exclusively in the liver, so the body can maintain a sufficient blood glucose concentration. In other cells, uptake happens by passive transport through one of the 14 GLUT proteins. In the other cell types, phosphorylation occurs through a hexokinase, whereupon glucose can no longer diffuse out of the cell.
The glucose transporter GLUT1 is produced by most cell types and is of particular importance for nerve cells and pancreatic Beta cell. GLUT3 is highly expressed in nerve cells. Glucose from the bloodstream is taken up by GLUT4 from (of the skeletal muscle and heart muscle) and .
The metabolic pathway that begins with molecules containing two to four carbon atoms (C) and ends in the glucose molecule containing six carbon atoms is called gluconeogenesis and occurs in all living organisms. The smaller starting materials are the result of other metabolic pathways. Ultimately almost all come from the assimilation of carbon dioxide in plants during photosynthesis. The free energy of formation of α--glucose is 917.2 kilojoules per mole. In humans, gluconeogenesis occurs in the liver and kidney,Leszek Szablewski: Glucose Homeostasis and Insulin Resistance. Bentham Science Publishers, 2011, , p. 46. but also in other cell types. In the liver about of glycogen are stored, in skeletal muscle about .Peter C. Heinrich: Löffler/Petrides Biochemie und Pathobiochemie. Springer-Verlag, 2014, , p. 389. However, the glucose released in muscle cells upon cleavage of the glycogen can not be delivered to the circulation because glucose is phosphorylated by the hexokinase, and a glucose-6-phosphatase is not expressed to remove the phosphate group. Unlike for glucose, there is no transport protein for glucose-6-phosphate. Gluconeogenesis allows the organism to build up glucose from other metabolites, including lactic acid or certain , while consuming energy. The renal can also produce glucose.
Glucose also can be found outside of living organisms in the ambient environment. Glucose concentrations in the atmosphere are detected via collection of samples by aircraft and are known to vary from location to location. For example, glucose concentrations in atmospheric air from inland China range from 0.8-20.1 pg/l, whereas east coastal China glucose concentrations range from 10.3-142 pg/l.
In other living organisms, other forms of fermentation can occur. The bacterium Escherichia coli can grow on nutrient media containing glucose as the sole carbon source. In some bacteria and, in modified form, also in archaea, glucose is degraded via the Entner-Doudoroff pathway.
Use of glucose as an energy source in cells is by either aerobic respiration, anaerobic respiration, or fermentation. The first step of glycolysis is the phosphorylation of glucose by a hexokinase to form glucose 6-phosphate. The main reason for the immediate phosphorylation of glucose is to prevent its diffusion out of the cell as the charged phosphate group prevents glucose 6-phosphate from easily crossing the cell membrane. Furthermore, addition of the high-energy phosphate group activates glucose for subsequent breakdown in later steps of glycolysis. At physiological conditions, this initial reaction is irreversible.
In anaerobic respiration, one glucose molecule produces a net gain of two ATP molecules (four ATP molecules are produced during glycolysis through substrate-level phosphorylation, but two are required by enzymes used during the process). In aerobic respiration, a molecule of glucose is much more profitable in that a maximum net production of 30 or 32 ATP molecules (depending on the organism) is generated, mostly by the energy of O.
Tumor cells often grow comparatively quickly and consume an above-average amount of glucose by glycolysis, which leads to the formation of lactate, the end product of fermentation in mammals, even in the presence of oxygen. This is called the Warburg effect. For the increased uptake of glucose in tumors various SGLT and GLUT are overly produced.
In yeast, ethanol is fermented at high glucose concentrations, even in the presence of oxygen (which normally leads to respiration rather than fermentation). This is called the Crabtree effect.
Glucose can also degrade to form carbon dioxide through abiotic means. This has been demonstrated to occur experimentally via oxidation and hydrolysis at 22˚C and a pH of 2.5.
Glucose and oxygen supply almost all the energy for the brain, so its availability influences psychological processes. When Hypoglycaemia, psychological processes requiring mental effort (e.g., self-control, effortful decision-making) are impaired. In the brain, which is dependent on glucose and oxygen as the major source of energy, the glucose concentration is usually 4 to 6 mM (5 mM equals 90 mg/dL), but decreases to 2 to 3 mM when fasting. Confusion occurs below 1 mM and coma at lower levels.
The glucose in the blood is called blood sugar. Blood sugar levels are regulated by glucose-binding nerve cells in the hypothalamus. In addition, glucose in the brain binds to glucose receptors of the reward system in the nucleus accumbens. The binding of glucose to the sweet receptor on the tongue induces a release of various hormones of energy metabolism, either through glucose or through other sugars, leading to an increased cellular uptake and lower blood sugar levels. Artificial sweeteners do not lower blood sugar levels.
The blood sugar content of a healthy person in the short-time fasting state, e.g. after overnight fasting, is about 70 to 100 mg/dL of blood (4 to 5.5 mM). In blood plasma, the measured values are about 10–15% higher. In addition, the values in the artery blood are higher than the concentrations in the vein blood since glucose is absorbed into the tissue during the passage of the capillary bed. Also in the capillary blood, which is often used for blood sugar determination, the values are sometimes higher than in the venous blood. The glucose content of the blood is regulated by the hormones insulin, incretin and glucagon.
Some glucose is converted to lactic acid by , which is then utilized as an energy source by brain cells; some glucose is used by intestinal cells and red blood cells, while the rest reaches the liver, adipose tissue and muscle cells, where it is absorbed and stored as glycogen (under the influence of insulin). Liver cell glycogen can be converted to glucose and returned to the blood when insulin is low or absent; muscle cell glycogen is not returned to the blood because of a lack of enzymes. In Adipocyte, glucose is used to power reactions that synthesize some fat types and have other purposes. Glycogen is the body's "glucose energy storage" mechanism, because it is much more "space efficient" and less reactive than glucose itself.
As a result of its importance in human health, glucose is an analyte in that are common medical . Eating or fasting prior to taking a blood sample has an effect on analyses for glucose in the blood; a high fasting glucose blood sugar level may be a sign of prediabetes or diabetes mellitus.
The glycemic index is an indicator of the speed of resorption and conversion to blood glucose levels from ingested carbohydrates, measured as the area under the curve of blood glucose levels after consumption in comparison to glucose (glucose is defined as 100).Richard A. Harvey, Denise R. Ferrier: Biochemistry. 5th Edition, Lippincott Williams & Wilkins, 2011, , p. 366. The clinical importance of the glycemic index is controversial,U Satyanarayana: Biochemistry. Elsevier Health Sciences, 2014, , p. 508. as foods with high fat contents slow the resorption of carbohydrates and lower the glycemic index, e.g. ice cream. An alternative indicator is the insulin index, measured as the impact of carbohydrate consumption on the blood insulin levels. The glycemic load is an indicator for the amount of glucose added to blood glucose levels after consumption, based on the glycemic index and the amount of consumed food.
Other than its direct use as a monomer, glucose can be broken down to synthesize a wide variety of other biomolecules. This is important, as glucose serves both as a primary store of energy and as a source of organic carbon. Glucose can be broken down and converted into . It is also a precursor for the synthesis of other important molecules such as vitamin C (ascorbic acid). In living organisms, glucose is converted to several other chemical compounds that are the starting material for various metabolic pathways. Among them, all other monosaccharidesPeter C. Heinrich: Löffler/Petrides Biochemie und Pathobiochemie. Springer-Verlag, 2014, , p. 27. such as fructose (via the polyol pathway),Peter C. Heinrich: Löffler/Petrides Biochemie und Pathobiochemie. Springer-Verlag, 2014, , p. 199, 200. mannose (the epimer of glucose at position 2), galactose (the epimer at position 4), fucose, various uronic acids and the are produced from glucose.Peter C. Heinrich: Löffler/Petrides Biochemie und Pathobiochemie. Springer-Verlag, 2014, , p. 214. In addition to the phosphorylation to glucose-6-phosphate, which is part of the glycolysis, glucose can be oxidized during its degradation to glucono-1,5-lactone. Glucose is used in some bacteria as a building block in the trehalose or the dextran biosynthesis and in animals as a building block of glycogen. Glucose can also be converted from bacterial xylose isomerase to fructose. In addition, glucose produce all nonessential amino acids, such as mannitol and sorbitol, , cholesterol and . Finally, glucose is used as a building block in the glycosylation of proteins to , , , and other substances (catalyzed by glycosyltransferases) and can be cleaved from them by .
To monitor the body's response to blood glucose-lowering therapy, glucose levels can be measured. Blood glucose monitoring can be performed by multiple methods, such as the fasting glucose test which measures the level of glucose in the blood after 8 hours of fasting. Another test is the 2-hour glucose tolerance test (GTT)for this test, the person has a fasting glucose test done, then drinks a 75-gram glucose drink and is retested. This test measures the ability of the person's body to process glucose. Over time the blood glucose levels should decrease as insulin allows it to be taken up by cells and exit the blood stream.
Many crops can be used as the source of starch. Maize, rice, wheat, cassava, potato, barley, sweet potato,Alan Davidson: The Oxford Companion to Food. OUP Oxford, 2014, , p. 527. corn husk and sago are all used in various parts of the world. In the United States, corn starch (from maize) is used almost exclusively. Some commercial glucose occurs as a component of invert sugar, a roughly 1:1 mixture of glucose and fructose that is produced from sucrose. In principle, cellulose could be hydrolyzed to glucose, but this process is not yet commercially practical.
In addition, various organic acids can be biotechnologically produced from glucose, for example by fermentation with Clostridium thermoaceticum to produce acetic acid, with Penicillium notatum for the production of araboascorbic acid, with Rhizopus delemar for the production of fumaric acid, with Aspergillus niger for the production of gluconic acid, with Candida brumptii to produce isocitric acid, with Aspergillus terreus for the production of itaconic acid, with Pseudomonas fluorescens for the production of 2-ketogluconic acid, with Gluconobacter suboxydans for the production of 5-ketogluconic acid, with Aspergillus oryzae for the production of kojic acid, with Lactobacillus delbrueckii for the production of lactic acid, with Lactobacillus brevis for the production of malic acid, with Propionibacter shermanii for the production of propionic acid, with Pseudomonas aeruginosa for the production of pyruvic acid and with Gluconobacter suboxydans for the production of tartaric acid.James A. Kent: Riegel's Handbook of Industrial Chemistry. Springer Science & Business Media, 2013, , p. 938. Potent, bioactive natural products like triptolide that inhibit mammalian transcription via inhibition of the XPB subunit of the general transcription factor TFIIH has been recently reported as a glucose conjugate for targeting hypoxic cancer cells with increased glucose transporter expression. Recently, glucose has been gaining commercial use as a key component of "kits" containing lactic acid and insulin intended to induce hypoglycemia and hyperlactatemia to combat different cancers and infections.
Glucose degradation
Energy source
Precursor
Pathology
Diabetes
Hypoglycemia management
Sources
+ Sugar content of selected common plant foods (in grams per 100 g) 19.9 63.5 20.0 0.15 1 50.4 56.7 8.0 60.8 16.2 96.2 77 0.0 14.3 60.3 high high 15.0 The carbohydrate value is calculated in the USDA database and does not always correspond to the sum of the sugars, the starch, and the "dietary fiber".
Commercial production
Conversion to fructose
Commercial usage
Analysis
Classical qualitative detection reactions
Fehling test
Tollens test
Barfoed test
Nylander's test
Other tests
Instrumental quantification
Refractometry and polarimetry
Photometric enzymatic methods in solution
Photometric test-strip method
Amperometric glucose sensor
Other sensory methods
Copper iodometry
Chromatographic methods
In vivo analysis
External links
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