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Glucose is a simple with the molecular formula 6126. Glucose circulates in the blood of animals as . It is made during from water and carbon dioxide, using energy from sunlight. It is the most important source of energy for cellular respiration. Glucose is stored as a , in plants as and in animals as .

With six carbon atoms, it is classed as a , a subcategory of the . D-Glucose is one of the sixteen . The D-, D-glucose, also known as dextrose, occurs widely in nature, but the L-isomer, , does not. Glucose can be obtained by of carbohydrates such as milk sugar (), cane sugar (), , , , etc. It is commonly commercially manufactured from cornstarch by hydrolysis via pressurized steaming at controlled pH in a jet followed by further enzymatic depolymerization."glucose." The Columbia Encyclopedia, 6th ed.. 2015. 17 Nov. 2015 . Unbonded glucose is one of the main ingredients of .

In 1747, was the first to isolate glucose.

(2018). 9780123849533, Academic Press. .
Glucose is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic . The name glucose derives through the French from the γλυκός, which means "sweet," in reference to , the sweet, first press of grapes in the making of .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 : 106–13. 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 Glucose (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 "" is a chemical classifier, denoting a .

Function in biology
Glucose is the most widely used in most living organisms. One possible explanation for this is that glucose has a lower tendency than other aldohexoses to react nonspecifically with the groups of . This reaction——impairs or destroys the function of many proteins. Glucose's low rate of glycation can be attributed to its having a more stable cyclic form compared to other aldohexoses, which means it spends less time than they do in its reactive open-chain form. The reason for glucose having the most stable cyclic form of all the aldohexoses is that its hydroxy groups (with the exception of the hydroxy group on the anomeric carbon of D-glucose) are in the equatorial position. Many of the long-term complications of diabetes (e.g., blindness, , and peripheral neuropathy) are probably due to the glycation of proteins or . In contrast, -regulated addition of sugars to protein is called and is essential for the function of many proteins.
9780879697709, Cold Spring Harbor Laboratories Press. .

Energy source
Glucose is a ubiquitous fuel in . It is used as an energy source in most organisms, from bacteria to humans, through either aerobic respiration, anaerobic respiration, or fermentation. Glucose is the human body's key source of energy, through aerobic respiration, providing about 3.75  (16 ) of per gram. Breakdown of carbohydrates (e.g., starch) yields and , most of which is glucose. Through and later in the reactions of the citric acid cycle and oxidative phosphorylation, glucose is to eventually form and , yielding energy mostly in the form of ATP. The insulin reaction, and other mechanisms, regulate the concentration of glucose in the blood.

Glucose supplies almost all the energy for the , so its availability influences processes. When , psychological processes requiring mental effort (e.g., , effortful decision-making) are impaired.

As a result of its importance in human health, glucose is an analyte in 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 level may be a sign of or diabetes mellitus.


[[File:Glucose metabolism.svg|thumb|Glucose metabolism and various forms of it in the process
Glucose-containing compounds and forms are digested and taken up by the body in the intestines, including , , and .
Glucose is stored in mainly the liver and muscles as glycogen. It is distributed and used in tissues as free glucose. ]]

Use of glucose as an energy source in cells is by either aerobic respiration, anaerobic respiration, or fermentation. All of these processes follow from an earlier metabolic pathway known as . The first step of glycolysis is the of glucose by a 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 group prevents glucose 6-phosphate from easily crossing the . 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) through oxidative phosphorylation is generated.

Organisms use glucose as a precursor for the synthesis of several important substances. , , and ("animal starch") are common glucose (). Some of these polymers (starch or glycogen) serve as energy stores, while others (cellulose and , which is made from a derivative of glucose) have structural roles. of glucose combined with other sugars serve as important energy stores. These include , the predominant sugar in milk, which is a glucose-galactose disaccharide, and , another disaccharide which is composed of glucose and . Glucose is also added onto certain proteins and in a process called . This is often critical for their functioning. The enzymes that join glucose to other molecules usually use glucose to power the formation of the new bond by coupling it with the breaking of the glucose-phosphate bond.

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 ().

Medical uses

Glucose in diabetes
Diabetes is a metabolic disorder where the body is unable to regulate either because of a lack of insulin in the body or the failure, by cells in the body, to respond properly to insulin. Each of these situations can be caused by persistently high elevations of blood glucose levels, through pancreatic burnout and insulin resistance. The is the organ responsible for the secretion of . Insulin is a hormone that regulates glucose levels, allowing the body's cells to absorb and use glucose. Without it, glucose cannot enter the cell and therefore cannot be used as fuel for the body's functions.Estela, Carlos (2011) "Blood Glucose Levels," Undergraduate Journal of Mathematical Modeling: One + Two: Vol. 3: Iss. 2, Article 12. If the pancreas is exposed to persistently high elevations of blood glucose levels, the in the pancreas could be damaged, causing a lack of insulin in the body. Insulin resistance occurs when the pancreas tries to produce more and more insulin in response to persistently elevated blood glucose levels. Eventually, the rest of the body becomes resistant to the insulin that the pancreas is producing, thereby requiring more insulin to achieve the same blood glucose-lowering effect, and forcing the pancreas to produce even more insulin to compete with the resistance. This negative spiral contributes to pancreatic burnout, and the disease progression of diabetes.

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.

Hypoglycemia management
Individuals with diabetes or other conditions that result in often carry small amounts of sugar in various forms. One sugar commonly used is glucose, often in the form of glucose tablets (glucose pressed into a tablet shape sometimes with one or more other ingredients as a binder), , or .

Structure and nomenclature
Glucose is a monosaccharide with formula C6H12O6 or H-(C=O)-(CHOH)5-H, whose five (OH) groups are arranged in a specific way along its six- back.

Open-chain form
In its fleeting form, the glucose molecule has an open (as opposed to ) and unbranched backbone of six carbon atoms, C-1 through C-6; where C-1 is part of an H(C=O)-, and each of the other five carbons bears one hydroxyl group -OH. The remaining of the backbone carbons are satisfied by atoms -H. Therefore, glucose is both a and an , or an . The aldehyde group makes glucose a giving a positive reaction with the .

Each of the four carbons C-2 through C-5 is a , meaning that its four bonds connect to four different substituents. (Carbon C-2, for example, connects to -(C=O)H, -OH, -H, and -(CHOH)4H.) In D-glucose, these four parts must be in a specific three-dimensional arrangement. Namely, when the molecule is drawn in the Fischer projection, the hydroxyls on C-2, C-4, and C-5 must be on the right side, while that on C-3 must be on the left side.

The positions of those four hydroxyls are exactly reversed in the Fischer diagram of . D- and L-glucose are two of the 16 possible aldohexoses; the other 14 are , , , , , , and , each with two , “D-” and “L-”.

It is important to note that the linear form of glucose makes up less than 3% of the glucose molecules in a water solution. The rest is one of two cyclic forms of glucose that are formed when the hydroxyl group on carbon 5 (C5) bonds to the aldehyde carbon 1 (C1).

Cyclic forms
In solutions, the open-chain form of glucose (either "-" or "-") exists in equilibrium with several cyclic isomers, each containing a ring of carbons closed by one oxygen atom. In aqueous solution however, more than 99% of glucose molecules, at any given time, exist as forms. The open-chain form is limited to about 0.25% and forms exists in negligible amounts. The terms "glucose" and "-glucose" are generally used for these cyclic forms as well. The ring arises from the open-chain form by an intramolecular nucleophilic addition reaction between the aldehyde group (at C-1) and either the C-4 or C-5 hydroxyl group, forming a linkage, -C(OH)H-O-.

The reaction between C-1 and C-5 yields a six-membered system called a pyranose, which is a monosaccharide sugar (hence "–ose") containing a derivatised skeleton. The (much rarer) reaction between C-1 and C-4 yields a five-membered furanose ring, named after the cyclic ether . 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 -(C(CH2OH)HOH)-H or -(CHOH)-H, respectively).

The ring-closing reaction makes carbon C-1 , too, since its four bonds lead to -H, to -OH, to carbon C-2, and to the ring oxygen. These four parts of the molecule may be arranged around C-1 (the ) in two distinct ways, designated by the prefixes "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 -CH2OH 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 .

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 rings are not planar, but are twisted in three dimensions. The glucopyranose ring (α or β) can assume several non-planar shapes, analogous to the "chair" and "boat" conformations of . Similarly, the glucofuranose ring may assume several shapes, analogous to the "envelope" conformations of .

In the solid state, only the glucopyranose forms are observed, forming colorless crystalline solids that are highly in water and but poorly soluble in and . They melt at ( α) and ( β), and at higher temperatures into and water.

Rotational isomers
Each glucose is subject to . Within the cyclic form of glucose, rotation may occur around the O6-C6-C5-O5 , termed the ω-angle, to form three staggered rotamer conformations called gauche- gauche (gg), gauche- trans (gt) and trans- gauche (tg).For methyl α-D-glucuopyranose at equilibrium, the ratio of molecules in each rotamer conformation is reported to be 57% gg, 38% gt, and 5% tg. See . There is a tendency for the ω-angle to adopt a gauche conformation, a tendency that is attributed to the .

Physical properties

All forms of glucose are colorless and easily soluble in water, , and several other solvents. They are only sparingly soluble in and .

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 , the four cyclic isomers interconvert over a time scale of hours, in a process called .. 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 . Mutarotation is considerably slower at temperatures close to .

Mutarotation consists of a temporary reversal of the ring-forming reaction, resulting in the open-chain form, followed by a reforming of the ring. The ring closure step may use a different -OH group than the one recreated by the opening step (thus switching between pyranose and furanose forms), or the new hemiacetal group created on C-1 may have the same or opposite handedness as the original one (thus switching between the α and β forms). Thus, though the open-chain form is barely detectable in solution, it is an essential component of the equilibrium.

Solid state
Depending on conditions, three major solid forms of glucose can be crystallised from water solutions: α-glucopyranose, β-glucopyranose, and β-glucopyranose hydrate.Fred W. Schenck "Glucose and Glucose-Containing Syrups" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim.

Optical activity
Whether in water or in the solid form, D- (+) glucose is dextrorotatory, meaning it will rotate the direction of clockwise as seen looking toward the light source. The effect is due to the of the molecules, and indeed the mirror-image isomer, L- (-)glucose, is levorotatory (rotates polarized light counterclockwise) by the same amount. The strength of the effect is different for each of the five .

Note that the D- prefix does not refer directly to the optical properties of the compound. It indicates that the C-5 chiral center has the same handedness as that of D-glyceraldehyde (which was so labeled because it is dextrorotatory). The fact that D-glucose is dextrorotatory is a combined effect of its four chiral centers, not just of C-5; and indeed some of the other D-aldohexoses are levorotatory.


In and some , glucose is a product of . Photosynthesis is when plants use sunlight to convert six carbon dioxide and six water molecules, into one glucose molecule and six oxygen molecules. Glucose is also formed by the breakdown of polymeric forms of glucose— (in animals and ) or (in plants); the cleavage of glycogen is termed , of starch, starch degradation. In animals, glucose is synthesized in the and from non-carbohydrate intermediates, such as , and , in the process of . In some deep-sea , glucose is produced by .

Glucose is produced commercially via the enzymatic hydrolysis of starch. Many crops can be used as the source of starch. , , , , and are all used in various parts of the world. In the , (from maize) is used almost exclusively. Most commercial glucose occurs as a component of , a roughly 1:1 mixture of glucose and . In principle, cellulose could be hydrolysed to glucose, but this process is not yet commercially practical. Glucose syrup, also known as , is essentially a purified of obtained from edible starch that has a dextrose equivalency (DE) of 20 or more. Dried corn syrup is glucose syrup with the water removed. Glucose has a DE of 100; dried has a DE of less than 20. Corn syrup has a DE between 20 and 95.
(2018). 008092655X, Academic Press. . 008092655X

Sources and absorption
Most dietary carbohydrates contain glucose, either as their only building block (as in the polysaccharides starch and ), or together with another monosaccharide (as in the hetero-polysaccharides and ). Unbounded glucose is one of the main ingredients of .

In the lumen of the and , the glucose oligo- and polysaccharides are broken down to monosaccharides by the and intestinal glycosidases. Other polysaccharides cannot be processed by the human intestine and require assistance by if they are to be broken down; the most notable exceptions are (-glucose) and (-glucose). Glucose is then transported across the of the by SLC5A1 (SGLT1), and later across their by SLC2A2 (GLUT2).

Some glucose is converted to by , which is then utilized as an energy source by ; some glucose is used by intestinal cells and , while the rest reaches the , and cells, where it is absorbed and stored as glycogen (under the influence of ). 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 , glucose is used to power reactions that synthesize some 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.

Glucose was first isolated from in 1747 by the German chemist Andreas Marggraf.Marggraf (1747) "Experiences chimiques faites dans le dessein de tirer un veritable sucre de diverses plantes, qui croissent dans nos contrées" Chemical, Histoire de l'académie royale des sciences et belles-lettres de Berlin, pp. 79–90. From page 90: "Les raisins secs, etant humectés d'une petite quantité d'eau, de maniere qu'ils mollissent, peuvent alors etre pilés, & le suc qu'on en exprime, etant depuré & épaissi, fournira une espece de Sucre." (Raisins, being moistened with a small quantity of water, in a way that they soften, can be then pressed, and the juice that is squeezed out, after being purified and thickened, will provide a sort of 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.

See also
  • 2,5-Dimethylfuran, a potential glucose-based
  • Fludeoxyglucose (18F)
  • Glucose transporter (GLUT)
    • GLUT1
    • GLUT2
  • Glycated hemoglobin
  • Peritoneal dialysis
  • Sugars in wine
  • Trinder glucose activity test

Further reading

External links

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