View source for Glucose

{{Chembox new
|   Name = Glucose
|   IUPACName = 6-(hydroxymethyl)oxane<br />-2,3,4,5-tetrol OR (2R,3R,4S,5R,6R)-6-(hydroxymethyl)tetrahydro- 2H-pyran-2,3,4,5-tetraol
|   ImageFile = Glucose-2D-skeletal.png
|   ImageFile1 = Beta-D-glucose-3D-vdW.png
<!--|   OtherNames = 
| dextrose
|-One indicator test for glucose would be testing it with glucose test paper.  Glucose test paper is paper that is usually orange or blue and will change color to a substance when glucose is present.
| Varieties of<small>D</small>-glucose
| ''α''-<small>D</small>-glucose; ''β''-<small>D</small>-glucose
|-
| Abbreviations
| '''Glc, CHO'''
|-
 -->
| Section1 = {{Chembox Identifiers
|   CASOther = 50-99-7 (<small>D</small>-glucose)
|   CASOther = 921-60-8 (<small>L</small>-glucose)
|   SMILES = C(C1C(C(C(C(O1)O)O)O)O)O
  }}
| Section2 = {{Chembox Properties
|   Formula = [[Carbon|C]]<sub>6</sub>[[Hydrogen|H]]<sub>12</sub>[[Oxygen|O]]<sub>6</sub>
|   MolarMass = 180.16 g mol<sup>−1</sup>
|   MeltingPt = ''α''-<small>D</small>-glucose: 146°C<br />''β''-<small>D</small>-glucose: 150°C
|   Density = 1.54 g cm<sup>−3</sup>}}
}}
{{SI}}
{{CMG}}

==Overview==
'''Glucose''' (Glc), a [[monosaccharide]] (or simple [[sugar]]), is an important [[carbohydrate]] in [[biology]]. The living [[Cell (biology)|cell]] uses it as a source of energy and metabolic intermediate. Glucose is one of the main products of [[photosynthesis]] and starts [[cellular respiration]] in both [[prokaryotes]] and [[eukaryotes]]. The name comes from the [[Greek language|Greek]] word ''glykys'' ({{lang|el|γλυκύς}}), which means "sweet", plus the suffix "-ose" which denotes a [[sugar]].

Two [[stereoisomerism|stereoisomer]]s of the [[aldohexose]] sugars are known as glucose, only one of which (<small>D</small>-glucose) is biologically active. This form (<small>D</small>-glucose) is often referred to as '''dextrose monohydrate''', or, especially in the food industry, simply '''dextrose''' (from ''dextrorotatory glucose''<ref>[http://www.m-w.com/dictionary/dextrose dextrose - Definition from the Merriam-Webster Online Dictionary<!-- Bot generated title -->]</ref>).  This article deals with the <small>D</small>-form of glucose. The mirror-image of the molecule, <small>L</small>-glucose, cannot be metabolized by cells in the biochemical process known as [[glycolysis]].

Glucose is commonly available in the form of a white substance or as a solid crystal.  It can also be commonly found as an [[aqueous solution]].

== Structure ==
Glucose (C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>) contains six [[carbon]] [[atom]]s one of which is part of an [[aldehyde]] group and is therefore referred to as an [[Hexose|aldohexose]]. In solution, the glucose molecule can exist in an open-chain (acyclic) and ring (cyclic) form (in equilibrium), the latter being the result of a covalent bond between the aldehyde C atom and the C-5 [[hydroxyl]] group to form a six-membered cyclic [[hemiacetal]]. At [[pH]] 7 the cyclic form is predominant. In the solid phase, glucose assumes the cyclic form. As the ring contains five carbon atoms and one oxygen atom, which resembles the structure of [[pyran]], the cyclic form of glucose is also referred to as glucopyranose. In this ring, each carbon is linked to a hydroxyl side group with the exception of the fifth atom, which links to a sixth carbon atom outside the ring, forming a CH<sub>2</sub>OH group. 
=== Isomers ===
[[Aldohexose]] sugars have 4 [[chirality (chemistry)|chiral centers]] giving 2<sup>4</sup> = 16 [[stereoisomers]]. These are split into two groups, <small>L</small> and <small>D</small>, with 8 sugars in each.  Glucose is one of these sugars, and <small>L</small> and <small>D</small>-glucose are two of the stereoisomers. Only 7 of these are found in living organisms, of which <small>D</small>-glucose (Glu), <small>D</small>-[[galactose]] (Gal) and <small>D</small>-[[mannose]] (Man) are the most important. These eight isomers (including glucose itself) are all [[diastereoisomer]]s in relation to each other and all belong to the [[Monosaccharide#Isomerism|<small>D</small>-series]]. 

An additional asymmetric center at C-1 (called ''the anomeric carbon atom'') is created when glucose cyclizes and two ring structures, called [[anomer]]s are formed &mdash; ''α''-glucose and ''β''-glucose. These anomers differ structurally with respect to the relative positioning of their hydroxyl group linked to C-1 and the group at C-6, which is termed the reference carbon. When <small>D</small>-glucose is drawn as a [[Haworth projection]] or in the standard chair conformation, the designation ''α'' means that the hydroxyl group attached to C-1 is positioned trans to the -CH<sub>2</sub>OH group at C-5, while ''β'' means it is cis. Another popular method of distinguishing ''α'' from ''β'' is by observing whether the C-1 hydroxyl is below or above the plane of the ring, respectively, but this method is an inaccurate definition and may fail if the glucose ring is drawn upside down or in an alternative chair conformation. The ''α'' and ''β'' forms interconvert over a timescale of hours in aqueous solution, to a final stable ratio of ''α'':''β'' 36:64, in a process called ''[[mutarotation]]''.<ref>{{cite book |title=Organic Chemistry |last=McMurry |first=John |year=1988 |publisher=Brooks/Cole |pages=866 |isbn=0534079687 }}</ref>

<gallery>
Image:D-glucose-chain-2D-Fischer.png|<center>The [[Fischer projection]] of the chain form of <small>D</small>-glucose</center>
Image:D-glucose-chain-2D-skeletal-numbers.png|<center>The chain form of <small>D</small>-glucose</center>
Image:Alpha-D-glucopyranose-2D-skeletal.png|<center>''α''-<small>D</small>-<br>glucopyranose</center>
Image:Beta-D-glucopyranose-2D-skeletal.png|<center>''β''-<small>D</small>-<br>glucopyranose</center>
Image:D-glucose-chain-3D-balls.png|<center>Chain form: [[ball-and-stick model]]</center>
Image:D-glucose-chain-3D-vdW.png|<center>Chain form: [[space-filling model]]</center>
Image:Alpha-D-glucose-3D-balls.png|<center>''α''-<small>D</small>-<br>glucopyranose</center>
Image:Beta-D-glucose-3D-balls.png|<center>''β''-<small>D</small>-<br>glucopyranose</center>
</gallery>

===Rotamers===
Within the cyclic form of glucose, rotation may occur around the O6-C6-C5-O5 torsion angle, termed the ω-angle, to form three rotamer conformations as shown in the diagram below. Referring to the orientations of the ω-angle and the O6-C6-C5-C4 angle the three stable staggered rotamer conformations are termed ''gauche''-''gauche'' (gg), ''gauche''-''trans'' (gt) and ''trans''-''gauche'' (tg). For methyl ''α''-<small>D</small>-glucopyranose at equilibrium the ratio of molecules in each rotamer conformation is reported as 57:38:5 gg:gt:tg.<ref>{{cite journal | author = Kirschner, K.N. Woods, R.J. | title = Solvent interactions determine carbohydrate conformation | journal = Proc. Natl. Acad. Sci. USA.  | year=2001 | volume=98 | issue=19 | pages=10541-10545 | id = PMID 11526221}}</ref>
This tendency for the ω-angle to prefer to adopt a ''gauche'' conformation is attributed to the [[gauche effect]].    
[[Image:Glc rotamers.jpeg|center|thumb|600px|Rotamer conformations of ''α''-<small>D</small>-glucopyranose]]

==Production==<!-- This section is linked from [[Sake]] -->
===Natural===
#Glucose is one of the products of [[photosynthesis]] in [[plants]] and some [[prokaryote]]s.
#In animals and fungi, glucose is the result of the breakdown of [[glycogen]], a process known as [[glycogenolysis]]. In plants the breakdown substrate is [[starch]].
#In animals, glucose is synthesized in the [[liver]] and [[kidney]]s from non-carbohydrate intermediates, such as [[pyruvate]] and [[glycerol]], by a process known as [[gluconeogenesis]].

===Commercial===  
Glucose is produced commercially via the [[enzyme|enzymatic]] [[hydrolysis]] of [[starch]]. Many crops can be used as the source of starch. [[Maize]], [[rice]], [[wheat]], [[potato]], cassava, arrowroot, and sago are all used in various parts of the world. In the [[United States]], [[cornstarch]] (from maize) is used almost exclusively.  
   
This enzymatic process has two stages. Over the course of 1-2 hours near 100 °C, enzymes hydrolyze starch into smaller carbohydrates containing on average 5-10 glucose units each. Some variations on this process briefly heat the starch mixture to 130 °C or hotter one or more times. This heat treatment improves the solubility of starch in water, but deactivates the enzyme, and fresh enzyme must be added to the mixture after each heating.

In the second step, known as "saccharification", the partially hydrolyzed starch is completely hydrolyzed to glucose using the [[glucoamylase]] enzyme from the [[fungus]] ''[[Aspergillus niger]]''. Typical reaction conditions are [[pH]] 4.0&ndash;4.5, 60 °C, and a carbohydrate concentration of 30&ndash;35% by weight. Under these conditions, starch can be converted to glucose at 96% yield after 1&ndash;4 days.  Still higher yields can be obtained using more dilute solutions, but this approach requires larger reactors and processing a greater volume of water, and is not generally economical.  The resulting glucose solution is then purified by [[filtration]] and concentrated in a multiple-effect evaporator. Solid D-glucose is then produced by repeated [[crystallization]]s.

<gallery>
image:Glucose 1.jpg|Glucose
image:Glucose 2.jpg|Glucose tablets
</gallery>

==Function==
We can speculate on the reasons why glucose, and not another monosaccharide such as fructose (Fru), is so widely used in evolution, the ecosystem, and metabolism. Glucose can form from [[formaldehyde]] under [[abiotic]] conditions, so it may well have been available to primitive [[biochemical]] systems. Probably more important to advanced life is the low tendency of glucose, by comparison to other hexose sugars, to non-specifically react with the [[amino]] groups of [[protein]]s. This reaction ([[glycation]]) reduces or destroys the function of many [[enzyme]]s. The low rate of glycation is due to glucose's preference for the less reactive cyclic [[isomer]]. Nevertheless, many of the long-term complications of [[diabetes]] (e.g., [[blindness]], [[renal failure|kidney failure]], and [[peripheral neuropathy]]) are probably due to the glycation of proteins or lipids. In contrast, [[enzyme]]-regulated addition of glucose to proteins by [[glycosylation]] is often essential to their function.

===As an energy source===
Glucose is a ubiquitous fuel in [[biology]]. It is used as an energy source in most organisms, from bacteria to humans. Use of glucose may be by either [[aerobic respiration|aerobic]] or [[anaerobic respiration]] ([[Fermentation (biochemistry)|fermentation]]). Carbohydrates are the human body's key source of energy, through aerobic respiration, providing approximately 3.75 [[kilocalorie]]s (16 [[kilojoule]]s) of [[food energy]] per [[gram]].<ref>http://www.fao.org/docrep/006/Y5022E/y5022e04.htm</ref> Breakdown of carbohydrates (e.g. [[starch]]) yields mono- and disaccharides, most of which is glucose. Through [[glycolysis]] and later in the reactions of the [[Citric acid cycle]] (TCAC), glucose is [[oxidize]]d to eventually form [[carbon dioxide|CO<sub>2</sub>]] and [[water]], yielding energy, mostly in the form of [[adenosine triphosphate|ATP]].  The insulin reaction, and other mechanisms, regulate the concentration of glucose in the blood. A high fasting blood sugar level is an indication of prediabetic and diabetic conditions.

Glucose is a primary source of energy for the brain, and hence its availability influences psychological processes. When glucose is low, psychological processes requiring mental effort (e.g., self-control) are impaired.<ref>{{cite journal | author = Fairclough, S. H., & Houston, K. | title = A metabolic measure of mental effort.| journal = Biological Psychology  | year=2004 | volume=66 |  pages=177-190}}</ref><ref>{{cite journal | author = Gailliot, M.T., Baumeister, R.F., DeWall, C.N., Maner, J.K., Plant, E.A., Tice, D.M., Brewer, L.E., & Schmeichel, B.J.  | title = Self-Control relies on glucose as a limited energy source: Willpower is more than a metaphor.| journal = Journal of Personality and Social Psychology | year=2007 | volume=92 |  pages=325-336}}</ref><ref>{{cite journal | author = Gailliot, M.T., & Baumeister, R.F.  | title = The physiology of willpower: Linking blood glucose to self-control.| journal = Personality and Social Psychology Review | year=in press}}</ref>

===Glucose in glycolysis===
{|width=370px align=right
|{{Enzymatic Reaction
|foward_enzyme=[[Hexokinase]]
|reverse_enzyme=
|substrate=α-<small>D</small>-Glucose
|product=α-<small>D</small>-[[Glucose-6-phosphate]]
|reaction_direction_(forward/reversible/reverse)=forward
|minor_foward_substrate(s)=[[Adenosine triphosphate|ATP]]
|minor_foward_product(s)=[[Adenosine diphosphate|ADP]]
|minor_reverse_substrate(s)=
|minor_reverse_product(s)=
|substrate_image=Glucose_wpmp.png
|product_image=Glucose-6-phosphate_wpmp.png
}}
|-
|
|}

Use of glucose as an energy source in cells is via aerobic or anaerobic respiration. Both of these start with the early steps of the [[glycolysis]] [[metabolic pathway]]. The first step of this is the [[phosphorylation]] of glucose by [[hexokinase]] to prepare it for later breakdown to provide energy.

The major reason for the immediate phosphorylation of glucose by a [[hexokinase]] is to prevent diffusion out of the cell. The phosphorylation adds a charged [[phosphate]] group so the [[glucose 6-phosphate]] cannot easily cross the [[cell membrane]]. Irreversible first steps of a metabolic pathway are common for regulatory purposes.

===As a [[precursor (chemistry)|precursor]] ===
Glucose is critical in the production of [[protein]]s and in [[lipid]] metabolism. Also, in plants and most animals, it is a [[precursor (chemistry)|precursor]] for [[vitamin C]] (ascorbic acid) production. It is modified for use in these processes by the glycolysis pathway.

Glucose is used as a precursor for the synthesis of several important substances. starch solution [[Starch]], [[cellulose]], and [[glycogen]] ("animal starch") are common glucose [[polymer]]s ([[polysaccharide]]s). [[Lactose]], the predominant sugar in milk, is a glucose-[[galactose]] disaccharide. In [[sucrose]], another important [[disaccharide]], glucose is joined to fructose. These synthesis processes also rely on the phosphorylation of glucose through the first step of glycolysis.

==Sources and absorption==
All major dietary carbohydrates contain glucose, either as their only building block, as in starch and [[glycogen]], or together with another monosaccharide, as in sucrose and lactose. In the lumen of the duodenum and small intestine, the oligo- and polysaccharides are broken down to monosaccharides by the pancreatic and intestinal glycosidases. Glucose is then transported across the apical membrane of the [[enterocytes]] by [[SLC5A1]], and later across their basal membrane by [[SLC2A2]].<ref>{{cite journal |last=Ferraris |first=Ronaldo P. |year=2001 |title=Dietary and developmental regulation of intestinal sugar transport |journal=Biochemical Journal |issue=360 |pages=265-276 |url=http://www.biochemj.org/bj/360/0265/bj3600265.htm |accessdate= 2007-12-21}}</ref> Some of the glucose goes directly toward fueling [[brain cells]] and [[erythrocytes]], while the rest makes its way to the [[liver]] and [[muscle]]s, where it is stored as [[glycogen]], and to [[adipose tissue|fat cells]], where it can be used to power reactions which synthesize some [[fat]]s. Glycogen is the body's auxiliary energy source, tapped and converted back into glucose when there is need for energy.

==See also==
* [[Blood glucose]] or Blood Sugar
* [[HbA1c]]
* [[2,5-Dimethylfuran|DMF]] (potential glucose-based [[biofuel]])
* [[Glycation]]
* [[Glycosylation]]
* [[Photosynthesis]]
* [[Fructose]]
{{Glycolysis}}

==References==
{{reflist|2}}

{{Carbohydrates}}

[[Category:Chemical pathology]]
[[Category:Monosaccharides]]
[[Category:Aldohexoses]]
[[Category:Nutrition]]
[[Category:Sweeteners]]

{{Link FA|id}}

[[ar:غلوكوز]]
[[be:Глюкоза]]
[[be-x-old:Глюкоза]]
[[bs:Glukoza]]
[[bg:Глюкоза]]
[[ca:Glucosa]]
[[cs:Glukóza]]
[[da:Glukose]]
[[de:Traubenzucker]]
[[et:Glükoos]]
[[es:Glucosa]]
[[eo:Glukozo]]
[[fr:Glucose]]
[[gl:Glicosa]]
[[ko:글루코스]]
[[hr:Glukoza]]
[[id:Glukosa]]
[[is:Glúkósi]]
[[it:Glucosio]]
[[he:גלוקוז]]
[[ka:გლუკოზა]]
[[la:Glucosium]]
[[lv:Glikoze]]
[[lt:Gliukozė]]
[[hu:Glükóz]]
[[mk:Глукоза]]
[[ms:Glukosa]]
[[nl:Glucose]]
[[ja:グルコース]]
[[no:Glukose]]
[[nn:Glukose]]
[[oc:Glucòsa]]
[[om:Glucose]]
[[pl:Glukoza]]
[[pt:Glicose]]
[[ro:Glucoză]]
[[ru:Глюкоза]]
[[simple:Glucose]]
[[sk:Glukóza]]
[[sl:Glukoza]]
[[sr:Глукоза]]
[[sh:Glukoza]]
[[su:Glukosa]]
[[fi:Glukoosi]]
[[sv:Glukos]]
[[te:గ్లూకోస్]]
[[th:กลูโคส]]
[[tr:Glikoz]]
[[uk:Глюкоза]]
[[zh:葡萄糖]]

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