Glucose is a simple

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or do ...

with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of

carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...

s. Glucose is mainly made by plants and most

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

during

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...

from water and carbon dioxide, using energy from sunlight, where it is used to make

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wa ...

in cell walls, the most abundant carbohydrate in the world. In energy metabolism, glucose is the most important source of energy in all

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fu ...

s. Glucose for metabolism is stored as a

polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

, in plants mainly as

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human die ...

and amylopectin, and in animals as glycogen. Glucose circulates in the blood of animals as

blood sugar Glycaemia, also known as blood sugar level, blood sugar concentration, or blood glucose level is the measure of glucose concentrated in the blood of humans or other animals. Approximately 4 grams of glucose, a simple sugar, is present in the b ...

. The naturally occurring form of glucose is -glucose, while -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 Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...

, 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 Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...

(, "wine, must"), from (, "sweet"). The suffix "

-ose The suffix -ose ( or ) is used in biochemistry to form the names of sugars. This Latin suffix means "full of", "abounding in", "given to", or "like". Numerous systems exist to name specific sugars more descriptively. Monosaccharides, the simplest ...

" is a chemical classifier, denoting a sugar.

History

Glucose was first isolated from

raisin A raisin is a dried grape. Raisins are produced in many regions of the world and may be eaten raw or used in cooking, baking, and brewing. In the United Kingdom, Ireland, New Zealand, and Australia, the word ''raisin'' is reserved for the ...

s in 1747 by the German chemist Andreas Marggraf. Glucose was discovered in grapes by another German chemist

Johann Tobias Lowitz Johann Tobias Lowitz (russian: Товий Егорович Ловиц 25 April 1757 – 7 December 1804) was a German-Russian chemist and pharmacist. He was among the first to notice the clarification of liquids by the use of charcoal for adsorpti ...

in 1792, and distinguished as being different from cane sugar ( sucrose). Glucose is the term coined by

Jean Baptiste Dumas Jean Baptiste André Dumas (14 July 180010 April 1884) was a French chemist, best known for his works on organic analysis and synthesis, as well as the determination of atomic weights (relative atomic masses) and molecular weights by measuring v ...

in 1838, which has prevailed in the chemical literature. Friedrich August Kekulé proposed the term dextrose (from the

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

, meaning "right"), because in aqueous solution of glucose, the plane of linearly polarized light is turned to the right. In contrast, -fructose (a ketohexose) and -glucose turn linearly polarized light to the left. The earlier notation according to the rotation of the plane of linearly polarized light (''d'' and ''l''-nomenclature) was later abandoned in favor of the - and -notation, which refers to the absolute configuration of the asymmetric center farthest from the carbonyl group, and in concordance with the configuration of - or -glyceraldehyde.John F. Robyt: ''Essentials of Carbohydrate Chemistry.'' Springer Science & Business Media, 2012, . p. 7. 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 Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J ...

. This understanding occurred largely as a result of the investigations of Emil Fischer, a German chemist who received the 1902

Nobel Prize in Chemistry ) , image = Nobel Prize.png , alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then "M ...

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 isomers, 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 Otto Fritz Meyerhof (; April 12, 1884 – October 6, 1951) was a German physician and biochemist who won the 1922 Nobel Prize in Physiology and Medicine. Biography Otto Fritz Meyerhof was born in Hannover, at Theaterplatz 16A (now:Rathenaustrasse ...

received the

Nobel Prize in Physiology or Medicine The Nobel Prize in Physiology or Medicine is awarded yearly by the Nobel Assembly at the Karolinska Institute for outstanding discoveries in physiology or medicine. The Nobel Prize is not a single prize, but five separate prizes that, accordi ...

in 1922.

Hans von Euler-Chelpin Hans Karl August Simon von Euler-Chelpin (15 February 1873 – 6 November 1964) was a German-born Swedish biochemist. He won the Nobel Prize in Chemistry in 1929 with Arthur Harden for their investigations on the fermentation of sugar and enzy ...

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". In 1947,

Bernardo Houssay Bernardo Alberto Houssay (April 10, 1887 – September 21, 1971) was an Argentine physiologist. Houssay was a co-recipient of the 1947 Nobel Prize for Physiology or Medicine for discovering the role played by pituitary hormones in regulating ...

(for his discovery of the role of the pituitary gland in the metabolism of glucose and the derived carbohydrates) as well as

Carl Carl may refer to: * Carl, Georgia, city in USA * Carl, West Virginia, an unincorporated community *Carl (name), includes info about the name, variations of the name, and a list of people with the name * Carl², a TV series * "Carl", an episode of ...

and Gerty Cori (for their discovery of the conversion of glycogen from glucose) received the Nobel Prize in Physiology or Medicine. In 1970, Luis Leloir was awarded the Nobel Prize in Chemistry for the discovery of glucose-derived sugar nucleotides in the biosynthesis of carbohydrates.

Chemical and physical properties

Glucose forms white or colorless solids that are highly soluble in water and acetic acid but poorly soluble in

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is ...

and

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

. They melt at (''α'') and (''β''), and decompose starting at with release of various volatile products, ultimately leaving a residue of

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...

.Wenyue Kang and Zhijun Zhang (2020): "Selective Production of Acetic Acid via Catalytic Fast Pyrolysis of Hexoses over Potassium Salts", ''Catalysts'', volume 10, pages 502-515. Glucose has a pK value of 12.16 at in water. With six carbon atoms, it is classed as a hexose, a subcategory of the monosaccharides. -Glucose is one of the sixteen aldohexose stereoisomers. The - isomer, -glucose, also known as ''dextrose'', occurs widely in nature, but the -isomer, -glucose, does not. Glucose can be obtained by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysi ...

of carbohydrates such as milk sugar ( lactose), cane sugar (sucrose), maltose,

, 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. Unbonded glucose is one of the main ingredients of

honey Honey is a sweet and viscous substance made by several bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of plants (primar ...

Structure and nomenclature

Glucose is usually present in solid form as a monohydrate with a closed pyran ring (dextrose hydrate). In aqueous solution, on the other hand, it is an open-chain to a small extent and is present predominantly as α- or β-

pyranose Pyranose is a collective term for saccharides that have a chemical structure that includes a six-membered ring consisting of five carbon atoms and one oxygen atom. There may be other carbons external to the ring. The name derives from its similarit ...

, which interconvert. From aqueous solutions, the three known forms can be crystallized: α-glucopyranose, β-glucopyranose and β-glucopyranose hydrate. Glucose is a building block of the disaccharides lactose and sucrose (cane or beet sugar), of

oligosaccharide An oligosaccharide (/ˌɑlɪgoʊˈsækəˌɹaɪd/; from the Greek ὀλίγος ''olígos'', "a few", and σάκχαρ ''sácchar'', "sugar") is a saccharide polymer containing a small number (typically two to ten) of monosaccharides (simple sug ...

s such as

raffinose Raffinose is a trisaccharide composed of galactose, glucose, and fructose. It can be found in beans, cabbage, brussels sprouts, broccoli, asparagus, other vegetables, and whole grains. Raffinose can be hydrolyzed to D-galactose and sucrose ...

and of polysaccharides such as

, amylopectin, glycogen, and

. The

glass transition temperature The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or ru ...

of glucose is and the Gordon–Taylor constant (an experimentally determined constant for the prediction of the glass transition temperature for different mass fractions of a mixture of two substances) is 4.5.Benjamin Caballero, Paul Finglas, Fidel Toldrá: ''Encyclopedia of Food and Health''. Academic Press (2016). , Volume 1, p. 76.

Open-chain form

The open-chain form of glucose makes up less than 0.02% of the glucose molecules in an aqueous solution. The rest is one of two cyclic hemiacetal forms. In its

open-chain In chemistry, an open-chain compound (also spelled as open chain compound) or acyclic compound (Greek prefix "α", ''without'' and "κύκλος", ''cycle'') is a compound with a linear structure, rather than a cyclic one. An open-chain compound ...

form, the glucose molecule has an open (as opposed to

cyclic Cycle, cycles, or cyclic may refer to: Anthropology and social sciences * Cyclic history, a theory of history * Cyclical theory, a theory of American political history associated with Arthur Schlesinger, Sr. * Social cycle, various cycles in so ...

) unbranched backbone of six carbon atoms, where C-1 is part of an

aldehyde group In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl group ...

. Therefore, glucose is also classified as an

aldose An aldose is a monosaccharide (a simple sugar) with a carbon backbone chain with a carbonyl group on the endmost carbon atom, making it an aldehyde, and hydroxyl groups connected to all the other carbon atoms. Aldoses can be distinguished from ...

, or an aldohexose. The aldehyde group makes glucose a reducing sugar giving a positive reaction with the

Fehling test In organic chemistry, Fehling's solution is a chemical reagent used to differentiate between water-soluble carbohydrate and ketone () functional groups, and as a test for reducing sugars and non-reducing sugars, supplementary to the Tollens' rea ...

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 exist as

forms. The open-chain form is limited to about 0.25%, and furanose forms exist 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

hemiacetal A hemiacetal or a hemiketal has the general formula R1R2C(OH)OR, where R1 or R2 is hydrogen or an organic substituent. They generally result from the addition of an alcohol to an aldehyde or a ketone, although the latter are sometimes called hemi ...

linkage, . The reaction between C-1 and C-5 yields a six-membered heterocyclic 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 In chemistry, a Haworth projection is a common way of writing a structural formula to represent the cyclic structure of monosaccharides with a simple three-dimensional perspective. Haworth projection approximate the shapes of the actual molec ...

, 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 Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

Α-d-glucose and β-d-glucose acid-catalyzed mechanism

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 Cyclopentane (also called C pentane) is a highly flammable alicyclic hydrocarbon with chemical formula C5H10 and CAS number 287-92-3, consisting of a ring of five carbon atoms each bonded with two hydrogen atoms above and below the plane. It occ ...

. 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).

Mutarotation

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 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. The open-chain form is thermodynamically unstable, and it spontaneously isomerizes 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 .

Optical activity

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

tautomer Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hy ...

s. 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 A polarimeter is a scientific instrument used to measure the angle of rotation caused by passing polarized light through an optically active substance.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.

Isomerisation

In dilute sodium hydroxide or other dilute bases, the monosaccharides

mannose Mannose is a sugar monomer of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylation of certain proteins. Several congenital disorders of glycosylat ...

, glucose and fructose interconvert (via a Lobry de Bruyn–Alberda–Van Ekenstein transformation), so that a balance between these isomers is formed. This reaction proceeds via an

enediol In organic chemistry, alkenols (shortened to enols) are a type of reactive structure or intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond (). The ter ...

Biochemical properties

Glucose is the most abundant monosaccharide. Glucose is also the most widely used aldohexose in most living organisms. One possible explanation for this is that glucose has a lower tendency than other aldohexoses to react nonspecifically with the

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...

groups of

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

s. This reaction—

glycation Glycation (sometimes called non-enzymatic glycosylation) is the covalent attachment of a sugar to a protein or lipid. Typical sugars that participate in glycation are glucose, fructose, and their derivatives. Glycation is the non-enzymatic proce ...

—impairs or destroys the function of many proteins, e.g. in

glycated hemoglobin Glycated hemoglobin, also known as HbA1c, glycohemoglobin, hemoglobin A1c, A1C, is a form of hemoglobin (Hb) that is chemically linked to a sugar. Most monosaccharides, including glucose, galactose and fructose, spontaneously (i.e. non-enzymat ...

. 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 -glucose) are in the equatorial position. Presumably, glucose is the most abundant natural monosaccharide because it is less glycated with proteins than other monosaccharides.Jeremy M. Berg: ''Stryer Biochemie.'' Springer-Verlag, 2017, , p. 531. (german) Another hypothesis is that glucose, being the only -aldohexose that has all five hydroxy substituents in the equatorial position in the form of β--glucose, is more readily accessible to chemical reactions, for example, for esterification or acetal formation. For this reason, -glucose is also a highly preferred building block in natural polysaccharides (glycans). Polysaccharides that are composed solely of glucose are termed glucans. Glucose is produced by plants through 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 A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

and

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

s, 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.

Neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa ...

s, 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 Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

(e.g.,

blindness Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment� ...

kidney failure Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...

, and peripheral neuropathy) are probably due to the glycation of proteins or

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids in ...

s. In contrast,

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

-regulated addition of sugars to protein is called glycosylation and is essential for the function of many proteins.

Uptake

Ingested glucose initially binds to the receptor for sweet taste on the tongue in humans. This complex of the proteins

T1R2 Taste receptor type 1 member 2 is a protein that in humans is encoded by the ''TAS1R2'' gene. The sweet taste receptor is predominantly formed as a dimer of T1R2 and T1R3 by which different organisms sense this taste. In songbirds, however, the T ...

and

T1R3 Taste receptor type 1 member 3 is a protein that in humans is encoded by the ''TAS1R3'' gene. The ''TAS1R3'' gene encodes the human homolog of mouse Sac taste receptor, a major determinant of differences between sweet-sensitive and -insensitive m ...

makes it possible to identify glucose-containing food sources. Glucose mainly comes from food—about per day is produced by conversion of food,Peter C. Heinrich: ''Löffler/Petrides Biochemie und Pathobiochemie.'' Springer-Verlag, 2014, , p. 404. but it is also synthesized from other metabolites in the body's cells. In humans, the breakdown of glucose-containing polysaccharides happens in part already during chewing by means of amylase, which is contained in

saliva Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can ...

, as well as by maltase, lactase, and sucrase on the

brush border A brush border (striated border or brush border membrane) is the microvilli-covered surface of simple cuboidal and simple columnar epithelium found in different parts of the body. Microvilli are approximately 100 nanometers in diameter and thei ...

of the small intestine. Glucose is a building block of many carbohydrates and can be split off from them using certain enzymes.

Glucosidases Glucosidases are the glycoside hydrolase enzymes categorized under the Enzyme Commission number, EC number 3.2.1. Function Alpha-glucosidases are enzymes involved in breaking down complex carbohydrates such as starch and glycogen into their mono ...

, a subgroup of the glycosidases, first catalyze the hydrolysis of long-chain glucose-containing polysaccharides, removing terminal glucose. In turn, disaccharides are mostly degraded by specific glycosidases to glucose. The names of the degrading enzymes are often derived from the particular poly- and disaccharide; inter alia, for the degradation of polysaccharide chains there are amylases (named after amylose, a component of starch), cellulases (named after cellulose), chitinases (named after chitin), and more. Furthermore, for the cleavage of disaccharides, there are maltase, lactase, sucrase, trehalase, and others. In humans, about 70 genes are known that code for glycosidases. They have functions in the digestion and degradation of glycogen, sphingolipids, mucopolysaccharides, and poly( ADP-ribose). Humans do not produce cellulases, chitinases, or trehalases, but the bacteria in the gut microbiota do. 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 Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...

with the help of glucose transporters via a secondary active transport mechanism called sodium ion-glucose symport via

sodium/glucose cotransporter 1 Sodium/glucose cotransporter 1 (SGLT1) also known as solute carrier family 5 member 1 is a protein in humans that is encoded by the gene which encodes the production of the SGLT1 protein to line the absorptive cells in the small intestine and t ...

(SGLT1). Further transfer occurs on the basolateral side of the intestinal epithelial cells via the glucose transporter

GLUT2 Glucose transporter 2 (GLUT2) also known as solute carrier family 2 (facilitated glucose transporter), member 2 (SLC2A2) is a transmembrane carrier protein that enables protein facilitated glucose movement across cell membranes. It is the princ ...

, as well uptake into liver cells, kidney cells, cells of the islets of Langerhans,

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa ...

s, astrocytes, and

tanycyte Tanycytes are special ependymal cells found in the third ventricle of the brain, and on the floor of the fourth ventricle and have processes extending deep into the hypothalamus. It is possible that their function is to transfer chemical signals f ...

s. Glucose enters the liver via the portal vein and is stored there as a cellular glycogen. In the liver cell, it is phosphorylated by

glucokinase Glucokinase () is an enzyme that facilitates phosphorylation of glucose to glucose-6-phosphate. Glucokinase occurs in cells in the liver and pancreas of humans and most other vertebrates. In each of these organs it plays an important role in t ...

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 A hexokinase is an enzyme that phosphorylates hexoses (six-carbon sugars), forming hexose phosphate. In most organisms, glucose is the most important substrate for hexokinases, and glucose-6-phosphate is the most important product. Hexo ...

, 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 β-cells.

GLUT3 Glucose transporter 3 (or GLUT3), also known as solute carrier family 2, facilitated glucose transporter member 3 (SLC2A3) is a protein that in humans is encoded by the ''SLC2A3'' gene. GLUT3 facilitates the transport of glucose across the pla ...

is highly expressed in nerve cells. Glucose from the bloodstream is taken up by GLUT4 from muscle cells (of the

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of m ...

and heart muscle) and

fat cell Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes through adipogenesis. I ...

GLUT14 Solute carrier family 2 (facilitated glucose transporter), member 14 is a protein that in humans is encoded by the SLC2A14 gene. Members of the glucose transporter (GLUT) family, including SLC2A14, are highly conserved integral membrane protein ...

is expressed exclusively in

testicle A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...

s. Excess glucose is broken down and converted into fatty acids, which are stored as

triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as ...

s. In the

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...

s, glucose in the urine is absorbed via SGLT1 and SGLT2 in the apical cell membranes and transmitted via GLUT2 in the basolateral cell membranes. About 90% of kidney glucose reabsorption is via SGLT2 and about 3% via SGLT1.

Biosynthesis

In plants and some

prokaryote A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Con ...

s, glucose is a product of

. Glucose is also formed by the breakdown of polymeric forms of glucose like glycogen (in animals and

mushroom A mushroom or toadstool is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground, on soil, or on its food source. ''Toadstool'' generally denotes one poisonous to humans. The standard for the name "mushroom" is ...

s) or starch (in plants). The cleavage of glycogen is termed glycogenolysis, the cleavage of starch is called starch degradation. 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 biomolecules come from the assimilation of carbon dioxide in plants and microbes 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

lactate Lactate may refer to: * Lactation, the secretion of milk from the mammary glands * Lactate, the conjugate base of lactic acid Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with w ...

or certain

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

s, while consuming energy. The renal

tubular cell The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure ca ...

s 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.

Glucose degradation

In humans, glucose is metabolized by glycolysis and the pentose phosphate pathway.H. Robert Horton, Laurence A. Moran, K. Gray Scrimgeour, Marc D. Perry, J. David Rawn: ''Biochemie''. Pearson Studium; 4. aktualisierte Auflage 2008; ; p. 490–496. (german) Glycolysis is used by all living organisms,Brian K. Hall: ''Strickberger's Evolution.'' Jones & Bartlett Publishers, 2013, , p. 164. with small variations, and all organisms generate energy from the breakdown of monosaccharides. In the further course of the metabolism, it can be completely degraded via oxidative decarboxylation, the

citric acid cycle The citric acid cycle (CAC)—also known as the Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and prot ...

(synonym ''Krebs cycle'') and the respiratory chain to water and carbon dioxide. If there is not enough oxygen available for this, the glucose degradation in animals occurs anaerobic to lactate via lactic acid fermentation and releases much less energy. Muscular lactate enters the liver through the bloodstream in mammals, where gluconeogenesis occurs (

Cori cycle The Cori cycle (also known as the lactic acid cycle), named after its discoverers, Carl Ferdinand Cori and Gerty Cori, is a metabolic pathway in which lactate, produced by anaerobic glycolysis in muscles, is transported to the liver and converted ...

). With a high supply of glucose, the metabolite acetyl-CoA from the Krebs cycle can also be used for

fatty acid synthesis In biochemistry, fatty acid synthesis is the creation of fatty acids from acetyl-CoA and NADPH through the action of enzymes called fatty acid synthases. This process takes place in the cytoplasm of the cell. Most of the acetyl-CoA which is co ...

. Glucose is also used to replenish the body's glycogen stores, which are mainly found in liver and skeletal muscle. These processes are hormonally regulated. In other living organisms, other forms of fermentation can occur. The bacterium ''

Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...

'' 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 In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, wh ...

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

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

group prevents glucose 6-phosphate from easily crossing the

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

. Furthermore, addition of the high-energy phosphate group activates glucose for subsequent breakdown in later steps of glycolysis. At

physiological condition Physiological condition or, more often "physiological conditions" is a term used in biology, biochemistry, and medicine. It refers to conditions of the external or internal milieu that may occur in nature for that organism or cell system, in contr ...

s, 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,.

Tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

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 Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...

, 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 The Crabtree effect, named after the English biochemist Herbert Grace Crabtree, describes the phenomenon whereby the yeast, ''Saccharomyces cerevisiae'', produces ethanol (alcohol) in aerobic conditions at high external glucose concentrations ra ...

. 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.

Energy source

Glucose is a ubiquitous fuel in

biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary ...

. It is used as an energy source in organisms, from bacteria to humans, through either

aerobic respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

anaerobic respiration Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain. In aerobic organisms undergoing r ...

(in bacteria), or fermentation. Glucose is the human body's key source of energy, through aerobic respiration, providing about 3.75

kilocalorie The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of ...

s (16 kilojoules) of food energy per gram. Breakdown of carbohydrates (e.g., starch) yields

mono- Numeral or number prefixes are prefixes derived from numerals or occasionally other numbers. In English and many other languages, they are used to coin numerous series of words. For example: * unicycle, bicycle, tricycle (1-cycle, 2-cycle, 3-cy ...

and disaccharides, most of which is glucose. Through

glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvate (). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH ...

and later in the reactions of the

and

oxidative phosphorylation Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine t ...

, glucose is

oxidize Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...

d to eventually form

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

and water, yielding energy mostly in the form of ATP. The insulin reaction, and other mechanisms, regulate the concentration of glucose in the blood. The physiological caloric value of glucose, depending on the source, is 16.2 kilojoules per gramGeorg Schwedt: ''Zuckersüße Chemie.'' John Wiley & Sons, 2012, , p. 100 . or 15.7 kJ/g (3.74 kcal/g). The high availability of carbohydrates from plant biomass has led to a variety of methods during evolution, especially in microorganisms, to utilize glucose for energy and carbon storage. Differences exist in which end product can no longer be used for energy production. The presence of individual genes, and their gene products, the enzymes, determine which reactions are possible. The metabolic pathway of glycolysis is used by almost all living beings. An essential difference in the use of glycolysis is the recovery of NADPH as a reductant for anabolism that would otherwise have to be generated indirectly. Glucose and oxygen supply almost all the energy for the

brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...

, so its availability influences psychological processes. When glucose is low, psychological processes requiring mental effort (e.g.,

self-control Self-control, an aspect of inhibitory control, is the ability to regulate one's emotions, thoughts, and behavior in the face of temptations and impulses. As an executive function, it is a cognitive process that is necessary for regulating one' ...

, 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 A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...

at lower levels. The glucose in the blood is called

. Blood sugar levels are regulated by glucose-binding nerve cells in the

hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus ...

. In addition, glucose in the brain binds to glucose receptors of the reward system in the

nucleus accumbens The nucleus accumbens (NAc or NAcc; also known as the accumbens nucleus, or formerly as the ''nucleus accumbens septi'', Latin for "nucleus adjacent to the septum") is a region in the basal forebrain rostral to the preoptic area of the hyp ...

. 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 sweetener A sugar substitute is a food additive that provides a sweetness like that of sugar while containing significantly less food energy than sugar-based sweeteners, making it a zero-calorie () or low-calorie sweetener. Artificial sweeteners may b ...

s 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 Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the int ...

, the measured values are about 10–15% higher. In addition, the values in the arterial blood are higher than the concentrations in the venous blood since glucose is absorbed into the tissue during the passage of the

capillary bed A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...

. 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. Insulin lowers the glucose level, glucagon increases it. Furthermore, the hormones adrenaline, thyroxine, glucocorticoids,

somatotropin Growth hormone (GH) or somatotropin, also known as human growth hormone (hGH or HGH) in its human form, is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans and other animals. It is thus important in ...

and

adrenocorticotropin Adrenocorticotropic hormone (ACTH; also adrenocorticotropin, corticotropin) is a polypeptide tropic hormone produced by and secreted by the anterior pituitary gland. It is also used as a medication and diagnostic agent. ACTH is an important co ...

lead to an increase in the glucose level. There is also a hormone-independent regulation, which is referred to as

glucose autoregulation Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

. After food intake the blood sugar concentration increases. Values over 180 mg/dL in venous whole blood are pathological and are termed hyperglycemia, values below 40 mg/dL are termed

hypoglycaemia Hypoglycemia, also called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's triad is used to properly identify hypoglycemic episodes. It is defined as blood glucose bel ...

. When needed, glucose is released into the bloodstream by glucose-6-phosphatase from glucose-6-phosphate originating from liver and kidney glycogen, thereby regulating the

homeostasis In biology, homeostasis ( British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and ...

of blood glucose concentration. In ruminants, the blood glucose concentration is lower (60 mg/dL in

cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Adult females are referred to as cows and adult ...

and 40 mg/dL in

sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticate ...

), because the carbohydrates are converted more by their gut microbiota into short-chain fatty acids.Harold A. Harper: ''Medizinische Biochemie''. Springer-Verlag, 2013, , p. 294. Some glucose is converted to

lactic acid Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as nat ...

by astrocytes, which is then utilized as an energy source by

brain cells Brain cells make up the functional tissue of the brain. The rest of the brain tissue is structural or connective called the stroma which includes blood vessels. The two main types of cells in the brain are neurons, also known as nerve cells, an ...

; some glucose is used by intestinal cells and

red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "hol ...

s, while the rest reaches the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...

, 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 fat cells, 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 glucose tests that are common medical blood tests. 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 prediabetes or

diabetes mellitus Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

. The

glycemic index The glycemic (glycaemic) index (GI; ) is a number from 0 to 100 assigned to a food, with pure glucose arbitrarily given the value of 100, which represents the relative rise in the blood glucose level two hours after consuming that food. The GI of ...

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 The insulin index of food represents how much it elevates the concentration of insulin in the blood during the two-hour period after the food is ingested. The index is similar to the glycemic index (GI) and glycemic load (GL), but rather than relyi ...

, 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.

Precursor

Organisms use glucose as a precursor for the synthesis of several important substances. Starch,

, and glycogen ("animal starch") are common glucose

s (polysaccharides). Some of these polymers (starch or glycogen) serve as energy stores, while others (cellulose and chitin, which is made from a derivative of glucose) have structural roles. Oligosaccharides of glucose combined with other sugars serve as important energy stores. These include lactose, the predominant sugar in milk, which is a glucose-galactose disaccharide, and sucrose, another disaccharide which is composed of glucose and fructose. Glucose is also added onto certain proteins and

s in a process called glycosylation. This is often critical for their functioning. The enzymes that join glucose to other molecules usually use phosphorylated 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

s. It is also a precursor for the synthesis of other important molecules such as

vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) ...

(ascorbic acid). In living organisms, glucose is converted to several other chemical compounds that are the starting material for various

metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical ...

s. 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

amino sugar In organic chemistry, an amino sugar (or more technically a 2-amino-2-deoxysugar) is a sugar molecule in which a hydroxyl group has been replaced with an amine group. More than 60 amino sugars are known, with one of the most abundant being ''N''- ...

s 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 Dextran is a complex branched glucan ( polysaccharide derived from the condensation of glucose), originally derived from wine. IUPAC defines dextrans as "Branched poly-α-d-glucosides of microbial origin having glycosidic bonds predominantly C- ...

biosynthesis and in animals as a building block of glycogen. Glucose can also be converted from bacterial xylose isomerase to fructose. In addition, glucose metabolites produce all nonessential amino acids, sugar alcohols such as mannitol and sorbitol,

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...

cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell memb ...

and nucleic acids. Finally, glucose is used as a building block in the glycosylation of proteins to

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glyco ...

glycolipid Glycolipids are lipids with a carbohydrate attached by a glycosidic (covalent) bond. Their role is to maintain the stability of the cell membrane and to facilitate cellular recognition, which is crucial to the immune response and in the conne ...

s, peptidoglycans,

glycoside In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...

s and other substances (catalyzed by glycosyltransferases) and can be cleaved from them by

glycosidase Glycoside hydrolases (also called glycosidases or glycosyl hydrolases) catalyze the hydrolysis of glycosidic bonds in complex sugars. They are extremely common enzymes with roles in nature including degradation of biomass such as cellulose ...

Pathology

Diabetes

Diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

is a metabolic disorder where the body is unable to regulate levels of glucose in the blood 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

pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an ...

is the organ responsible for the secretion of the hormones insulin and glucagon. 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. If the pancreas is exposed to persistently high elevations of blood glucose levels, the insulin-producing cells 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 low blood sugar 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),

hard candy A hard candy (American English), or boiled sweet (British English), is a sugar candy prepared from one or more sugar-based syrups that is heated to a temperature of 160 °C (320 °F) to make candy. Among the many hard candy varietie ...

, or sugar packet.

Sources

Most dietary carbohydrates contain glucose, either as their only building block (as in the polysaccharides starch and glycogen), or together with another monosaccharide (as in the hetero-polysaccharides sucrose and lactose). Unbound glucose is one of the main ingredients of honey. Glucose is extremely abundant and has been isolated from a variety of natural sources across the world, including male cones of the coniferous tree ''Wollemia nobilis'' in Rome, the roots of ''Ilex asprella'' plants in China, and straws from rice in California. 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

Glucose is produced industrially from starch by enzymatic

using

glucose amylase Glucan 1,4-α-glucosidase (EC 3.2.1.3, glucoamylase, amyloglucosidase', γ-amylase, lysosomal α-glucosidase, acid maltase, exo-1,4-α-glucosidase, glucose amylase, γ-1,4-glucan glucohydrolase, acid maltase, 1,4-α-D-glucan glucohydrolase) is an ...

or by the use of acids. Enzymatic hydrolysis has largely displaced acid-catalyzed hydrolysis reactions.P. J. Fellows: ''Food Processing Technology. Woodhead Publishing'', 2016, , p. 197. The result is glucose syrup (enzymatically with more than 90% glucose in the dry matter) with an annual worldwide production volume of 20 million tonnes (as of 2011).Thomas Becker, Dietmar Breithaupt, Horst Werner Doelle, Armin Fiechter, Günther Schlegel, Sakayu Shimizu, Hideaki Yamada: ''Biotechnology'', in: ''Ullmann's Encyclopedia of Industrial Chemistry'', 7th Edition, Wiley-VCH, 2011. . Volume 6, p. 48. This is the reason for the former common name "starch sugar". The amylases most often come from '' Bacillus licheniformis''The Amylase Research Society of Japan: ''Handbook of Amylases and Related Enzymes.'' Elsevier, 2014, , p. 195. or '' Bacillus subtilis'' (strain MN-385), which are more thermostable than the originally used enzymes. Starting in 1982, pullulanases from '' Aspergillus niger'' were used in the production of glucose syrup to convert amylopectin to starch (amylose), thereby increasing the yield of glucose. The reaction is carried out at a pH = 4.6–5.2 and a temperature of 55–60 °C.

Corn syrup Corn syrup is a food syrup which is made from the starch of corn (called maize in many countries) and contains varying amounts of sugars: glucose, maltose and higher oligosaccharides, depending on the grade. Corn syrup is used in foods to soft ...

has between 20% and 95% glucose in the dry matter. The Japanese form of the glucose syrup, Mizuame, is made from sweet potato or

rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and '' Porteresia'', both wild and domesticat ...

starch. Maltodextrin contains about 20% glucose. Many crops can be used as the source of starch.

Maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American English, North American and Australian English), is a cereal grain first domesticated by indigenous peoples of Mexico, indigenous ...

, rice,

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

cassava ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names), is a woody shrub of the spurge family, Euphorbiaceae, native to South America. Although a perennial plant, cassava is extensively cultivated ...

potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Uni ...

barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley p ...

, 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 The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

corn starch Corn starch, maize starch, or cornflour (British English) is the starch derived from corn (maize) grain. The starch is obtained from the endosperm of the kernel. Corn starch is a common food ingredient, often used to thicken sauces or sou ...

(from maize) is used almost exclusively. Some commercial glucose occurs as a component of

invert sugar Inverted sugar syrup, also called invert syrup, invert sugar, simple syrup, sugar syrup, sugar water, bar syrup, syrup USP, or sucrose inversion, is a syrup mixture of the monosaccharides glucose and fructose, that is made by hydrolytic s ...

, 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.

Conversion to fructose

In the US, almost exclusively corn (more precisely, corn syrup) is used as glucose source for the production of

isoglucose High-fructose corn syrup (HFCS), also known as glucose–fructose, isoglucose and glucose–fructose syrup, is a sweetener made from corn starch. As in the production of conventional corn syrup, the starch is broken down into glucose by enzym ...

, which is a mixture of glucose and fructose, since fructose has a higher sweetening powerwith same physiological calorific value of 374 kilocalories per 100 g. The annual world production of isoglucose is 8 million tonnes (as of 2011). When made from corn syrup, the final product is high-fructose corn syrup (HFCS).

Commercial usage

Glucose is mainly used for the production of fructose and of glucose-containing foods. In foods, it is used as a sweetener, humectant, to increase the

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). ...

and to create a softer

mouthfeel Mouthfeel refers to the physical sensations in the mouth caused by food or drink, making it distinct from taste. It is a fundamental sensory attribute which, along with taste and smell, determines the overall flavor of a food item. Mouthfeel ...

. Various sources of glucose, such as grape juice (for wine) or malt (for beer), are used for fermentation to ethanol during the production of

alcoholic beverage An alcoholic beverage (also called an alcoholic drink, adult beverage, or a drink) is a drink that contains ethanol, a type of Alcohol (chemistry), alcohol that acts Alcohol (drug), as a drug and is produced by Ethanol fermentation, fermentat ...

s. Most soft drinks in the US use HFCS-55 (with a fructose content of 55% in the dry mass), while most other HFCS-sweetened foods in the US use HFCS-42 (with a fructose content of 42% in the dry mass). In Mexico, on the other hand, soft drinks are sweetened by cane sugar, which has a higher sweetening power. In addition, glucose syrup is used, inter alia, in the production of confectionery such as candies,

toffee Toffee is a confection made by caramelizing sugar or molasses (creating inverted sugar) along with butter, and occasionally flour. The mixture is heated until its temperature reaches the hard crack stage of . While being prepared, toffee ...

and fondant.Steve T. Beckett: ''Beckett's Industrial Chocolate Manufacture and Use''. John Wiley & Sons, 2017, , p. 82. Typical chemical reactions of glucose when heated under water-free conditions are caramelization and, in presence of amino acids, the

Maillard reaction The Maillard reaction ( ; ) is a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavor. Seared steaks, fried dumplings, cookies and other kinds of biscuits, breads, toasted marshmallows, and m ...

. In addition, various organic acids can be biotechnologically produced from glucose, for example by fermentation with ''

Clostridium thermoaceticum ''Moorella thermoacetica'', previously known as ''Clostridium thermoaceticum'', is an acetogenic, thermophilic, strictly anaerobic, endospore-forming, bacterium belonging to the phylum Bacillota. Researchers at the Lawrence Berkeley National L ...

'' to produce acetic acid, with '' Penicillium notatum'' for the production of araboascorbic acid, with ''

Rhizopus delemar ''Rhizopus'' is a genus of common saprophytic fungi on plants and specialized parasites on animals. They are found in a wide variety of organic substances, including "mature fruits and vegetables", jellies, syrups, leather, bread, peanuts, and t ...

'' for the production of fumaric acid, with '' Aspergillus niger'' for the production of

gluconic acid Gluconic acid is an organic compound with molecular formula C6H12O7 and condensed structural formula HOCH2(CHOH)4COOH. It is one of the 16 stereoisomers of 2,3,4,5,6-pentahydroxyhexanoic acid. In aqueous solution at neutral pH, gluconic acid ...

, with ''

Candida brumptii Candida, or Cándida (Spanish), may refer to: Biology and medicine * ''Candida'' (fungus), a genus of yeasts ** Candidiasis, an infection by ''Candida'' organisms * Malvasia Candida, a variety of grape Places * Candida, Campania, a ''comu ...

'' to produce

isocitric acid Isocitric acid is a structural isomer of citric acid. Since citric acid and isocitric acid are structural isomers, they share similar physical and chemical properties. Due to these similar properties, it is difficult to separate the isomers. Salts ...

, with '' Aspergillus terreus'' for the production of itaconic acid, with '' Pseudomonas fluorescens'' for the production of 2-ketogluconic acid, with ''

Gluconobacter suboxydans ''Gluconobacter'' is a genus of bacteria in the acetic acid bacteria family. They prefer sugar-rich environments, so are sometimes found as a spoilage organism in beer. They are not known to be pathogenic but can cause rot in apples and pears ...

'' for the production of 5-ketogluconic acid, with '' Aspergillus oryzae'' for the production of kojic acid, with '' Lactobacillus delbrueckii'' for the production of

, with '' Lactobacillus brevis'' for the production of malic acid, with ''

Propionibacter shermanii ''Propionibacterium freudenreichii'' is a gram-positive, non-motile bacterium that plays an important role in the creation of Emmental cheese, and to some extent, Jarlsberg cheese, Leerdammer and Maasdam cheese. Its concentration in Swiss-type c ...

'' for the production of propionic acid, with ''

Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common encapsulated, gram-negative, aerobic– facultatively anaerobic, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, ''P. a ...

'' for the production of pyruvic acid and with ''

'' 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.

Analysis

When a glucose molecule is to be detected at a certain position in a larger molecule, nuclear magnetic resonance spectroscopy, X-ray crystallography analysis or lectin

immunostaining In biochemistry, immunostaining is any use of an antibody-based method to detect a specific protein in a sample. The term "immunostaining" was originally used to refer to the immunohistochemical staining of tissue sections, as first described by ...

is performed with concanavalin A reporter enzyme conjugate, which binds only glucose or mannose.

Classical qualitative detection reactions

These reactions have only historical significance:

Fehling test

The

is a classic method for the detection of aldoses.H. Fehling: ''Quantitative Bestimmung des Zuckers im Harn''. In: '' Archiv für physiologische Heilkunde'' (1848), volume 7, p. 64–73 (in German). Due to mutarotation, glucose is always present to a small extent as an open-chain aldehyde. By adding the Fehling reagents (Fehling (I) solution and Fehling (II) solution), the aldehyde group is oxidized to a carboxylic acid, while the Cu²⁺ tartrate complex is reduced to Cu⁺ and forms a brick red precipitate (Cu₂O).

Tollens test

In the

Tollens test Tollens' reagent (chemical formula Ag(NH3)2OH) is a chemical reagent used to distinguish between aldehydes and ketones along with some alpha-hydroxy ketones which can tautomerize into aldehydes. The reagent consists of a solution of silver ...

, after addition of ammoniacal AgNO₃ to the sample solution, glucose reduces Ag⁺ to elemental

silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...

Barfoed test

In Barfoed's test, a solution of dissolved

copper acetate Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-or ...

, sodium acetate and acetic acid is added to the solution of the sugar to be tested and subsequently heated in a water bath for a few minutes. Glucose and other monosaccharides rapidly produce a reddish color and reddish brown

copper(I) oxide Copper(I) oxide or cuprous oxide is the inorganic compound with the formula Cu2O. It is one of the principal oxides of copper, the other being or copper(II) oxide or cupric oxide (CuO). This red-coloured solid is a component of some antifoulin ...

(Cu₂O).

Nylander's test

As a reducing sugar, glucose reacts in the

Nylander's test Nylander's test is a chemical test used for detecting the presence of reducing sugars. Glucose or fructose reduces bismuth oxynitrate to bismuth Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a post-transition met ...

Other tests

Upon heating a dilute

potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...

solution with glucose to 100 °C, a strong reddish browning and a caramel-like odor develops.Georg Schwedt: ''Zuckersüße Chemie''. John Wiley & Sons, 2012, , p. 102 (in German). Concentrated

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...

dissolves dry glucose without blackening at room temperature forming sugar sulfuric acid. In a yeast solution, alcoholic fermentation produces carbon dioxide in the ratio of 2.0454 molecules of glucose to one molecule of CO₂. Glucose forms a black mass with stannous chloride. In an ammoniacal silver solution, glucose (as well as lactose and dextrin) leads to the deposition of silver. In an ammoniacal lead acetate solution, white

lead glycoside Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...

is formed in the presence of glucose, which becomes less soluble on cooking and turns brown. In an ammoniacal copper solution, yellow copper oxide hydrate is formed with glucose at room temperature, while red copper oxide is formed during boiling (same with dextrin, except for with an ammoniacal copper acetate solution). With Hager's reagent, glucose forms

mercury oxide Mercury oxide can refer to: * Mercury(I) oxide (mercurous oxide), Hg2O * Mercury(II) oxide Mercury(II) oxide, also called mercuric oxide or simply mercury oxide, is the inorganic compound with the formula Hg O. It has a red or orange color. Mer ...

during boiling. An alkaline bismuth solution is used to precipitate elemental, black-brown bismuth with glucose. Glucose boiled in an ammonium molybdate solution turns the solution blue. A solution with indigo carmine and sodium carbonate destains when boiled with glucose.

Instrumental quantification

Refractometry and polarimetry

In concentrated solutions of glucose with a low proportion of other carbohydrates, its concentration can be determined with a polarimeter. For sugar mixtures, the concentration can be determined with a refractometer, for example in the Oechsle determination in the course of the production of wine.

Photometric enzymatic methods in solution

The enzyme glucose oxidase (GOx) converts glucose into gluconic acid and hydrogen peroxide while consuming oxygen. Another enzyme, peroxidase, catalyzes a chromogenic reaction (Trinder reaction) of

phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it r ...

with

4-aminoantipyrine Ampyrone is a metabolite of aminopyrine with analgesic, anti-inflammatory, and antipyretic properties. Its use as a drug is discouraged due to the risk of agranulocytosis. It is used as a reagent for biochemical reactions producing peroxides or ...

to a purple dye.

Photometric test-strip method

The test-strip method employs the above-mentioned enzymatic conversion of glucose to gluconic acid to form hydrogen peroxide. The reagents are immobilised on a polymer matrix, the so-called test strip, which assumes a more or less intense color. This can be measured reflectometrically at 510 nm with the aid of an LED-based handheld photometer. This allows routine blood sugar determination by nonscientists. In addition to the reaction of phenol with 4-aminoantipyrine, new chromogenic reactions have been developed that allow photometry at higher wavelengths (550 nm, 750 nm).

Amperometric glucose sensor

The electroanalysis of glucose is also based on the enzymatic reaction mentioned above. The produced hydrogen peroxide can be amperometrically quantified by anodic oxidation at a potential of 600 mV. The GOx is immobilized on the electrode surface or in a membrane placed close to the electrode. Precious metals such as platinum or gold are used in electrodes, as well as carbon nanotube electrodes, which e.g. are doped with boron. Cu–CuO nanowires are also used as enzyme-free amperometric electrodes, reaching a detection limit of 50 μmol/L. A particularly promising method is the so-called "enzyme wiring", where the electron flowing during the oxidation is transferred via a molecular wire directly from the enzyme to the electrode.

Other sensory methods

There are a variety of other chemical sensors for measuring glucose. Given the importance of glucose analysis in the life sciences, numerous optical probes have also been developed for saccharides based on the use of boronic acids, which are particularly useful for intracellular sensory applications where other (optical) methods are not or only conditionally usable. In addition to the organic boronic acid derivatives, which often bind highly specifically to the 1,2-diol groups of sugars, there are also other probe concepts classified by functional mechanisms which use selective glucose-binding proteins (e.g. concanavalin A) as a receptor. Furthermore, methods were developed which indirectly detect the glucose concentration via the concentration of metabolized products, e.g. by the consumption of oxygen using fluorescence-optical sensors. Finally, there are enzyme-based concepts that use the intrinsic absorbance or fluorescence of (fluorescence-labeled) enzymes as reporters.

Copper iodometry

Glucose can be quantified by copper iodometry.

Chromatographic methods

In particular, for the analysis of complex mixtures containing glucose, e.g. in honey, chromatographic methods such as

high performance liquid chromatography High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify each component in a mixture. It relies on pumps to p ...

and gas chromatography are often used in combination with mass spectrometry. Taking into account the isotope ratios, it is also possible to reliably detect honey adulteration by added sugars with these methods. Derivatization using silylation reagents is commonly used. Also, the proportions of di- and trisaccharides can be quantified.

In vivo analysis

Glucose uptake in cells of organisms is measured with 2-deoxy-D-glucose or fluorodeoxyglucose.Donard Dwyer: ''Glucose Metabolism in the Brain.'' Academic Press, 2002, , p. XIII. (¹⁸F)fluorodeoxyglucose is used as a tracer in positron emission tomography in oncology and neurology, Gesellschaft Deutscher Chemiker
wayback=20100331071121 ''Anlagen zum Positionspapier der Fachgruppe Nuklearchemie''
, February 2000. where it is by far the most commonly used diagnostic agent.

References

External links

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