Editing Disaccharide

{{Short description|Complex sugar}}
[[File:Sucrose molecule.svg|thumb|287x287px|Sucrose, a disaccharide formed from condensation of a molecule of glucose and a molecule of fructose]]
A '''disaccharide''' (also called a '''double sugar''' or '''''biose''''')<ref>{{cite web |title=Biose |url=http://www.merriam-webster.com/medical/biose |website=[[Merriam-Webster]]}}</ref> is the [[sugar]] formed when two [[monosaccharide]]s are joined by [[glycosidic linkage]].<ref>{{GoldBookRef|title=disaccharides|file=D01776}}</ref> Like monosaccharides, disaccharides are simple sugars [[solubility|soluble]] in water. Three common examples are [[sucrose]], [[lactose]], and [[maltose]].

Disaccharides are one of the four chemical groupings of [[carbohydrate]]s (monosaccharides, disaccharides, [[oligosaccharide]]s, and [[polysaccharide]]s). The most common types of disaccharides—sucrose, lactose, and maltose—have 12 [[carbon]] atoms, with the general formula C<sub>12</sub>H<sub>22</sub>O<sub>11</sub>. The differences in these disaccharides are due to [[Isomer|atomic arrangements within the molecule]].<ref>{{cite book|title=Biology- A course for O Level|page=59|isbn=9810190964|last1=Kwan|first1=Lam Peng|year=2000}}</ref>

The joining of monosaccharides into a double sugar happens by a [[condensation reaction]], which involves the elimination of a water molecule from the [[functional group]]s only. Breaking apart a double sugar into its two monosaccharides is accomplished by [[hydrolysis]] with the help of a type of [[enzyme]] called a [[disaccharidase]]. As building the larger sugar ejects a water molecule, breaking it down consumes a water molecule. These reactions are vital in [[metabolism]]. Each disaccharide is broken down with the help of a corresponding disaccharidase ([[sucrase]], [[lactase]], and [[maltase]]).

==Classification==
There are two functionally different classes of disaccharides: 
*'''Reducing disaccharides''', in which one monosaccharide, the [[reducing sugar]] of the pair, still has a free [[hemiacetal]] unit that can perform as a reducing [[aldehyde]] group; [[lactose]], [[maltose]] and [[cellobiose]] are examples of reducing disaccharides, each with one hemiacetal unit, the other occupied by the [[glycosidic bond]], which prevents it from acting as a [[reducing agent]]. They can easily be detected by the Woehlk test or Fearon's test on [[methylamine]].<ref>{{Cite journal|title=How to visualize the different lactose content of dairy products by Fearon's test and Woehlk test in classroom experiments and a new approach to the mechanisms and formulae of the mysterious red dyes|journal = [[Chemistry Teacher International]]|language=en|doi = 10.1515/cti-2019-0008|year = 2019|last1 = Ruppersberg|first1 = Klaus|last2 = Herzog|first2 = Stefanie|last3 = Kussler|first3 = Manfred W.|last4 = Parchmann|first4 = Ilka| volume=2 | issue=2 |doi-access = free}}</ref>
*'''Non-reducing disaccharides''', in which the component monosaccharides bond through an [[acetal]] linkage between their [[anomer]]ic centers. This results in neither monosaccharide being left with a hemiacetal unit that is free to act as a reducing agent. [[Sucrose]] and [[trehalose]] are examples of non-reducing disaccharides because their glycosidic bond is between their respective hemiacetal carbon atoms. The reduced chemical reactivity of the non-reducing sugars, in comparison to reducing sugars, may be an advantage where stability in storage is important.<ref>{{cite web |title=Nomenclature of Carbohydrates (Recommendations 1996): 2-Carb-36 |url=http://www.chem.qmul.ac.uk/iupac/2carb/36.html |url-status=dead |archive-url=https://web.archive.org/web/20170826141346/http://www.chem.qmul.ac.uk/iupac/2carb/36.html |archive-date=2017-08-26 |access-date=2010-07-21 |website=chem.qmul.ac.uk}}</ref><ref>{{cite web |title=Disaccharides and Oligosaccharides |url=http://faculty.virginia.edu/mcgarveylab/Carbsyn/Carblist/html/disacch.html |access-date=2008-01-29 |website=University of Virginia Faculty and Lab Site |archive-date=2018-11-18 |archive-url=https://web.archive.org/web/20181118183515/http://faculty.virginia.edu/mcgarveylab/Carbsyn/Carblist/html/disacch.html |url-status=dead }}</ref>

==Formation==
The formation of a disaccharide molecule from two [[monosaccharide]] molecules proceeds by displacing a [[hydroxy group]] from one molecule and a [[Hydrogen atom|hydrogen nucleus]] (a [[proton]]) from the other, so that the new vacant bonds on the monosaccharides join the two [[monomer]]s together. Because of the removal of the water molecule from the product, the term of convenience for such a process is "[[dehydration reaction]]" (also "[[condensation reaction]]" or "[[Dehydration reaction|dehydration synthesis]]"). For example, milk sugar (lactose) is a disaccharide made by condensation of one molecule of each of the monosaccharides [[glucose]] and [[galactose]], whereas the disaccharide sucrose in sugar cane and sugar beet, is a condensation product of glucose and [[fructose]]. [[Maltose]], another common disaccharide, is condensed from two glucose molecules.<ref>{{cite book |last=Whitney |first=Ellie |url=https://archive.org/details/understandingnu000whit |title=Understanding Nutrition |author2=Sharon Rady Rolfes |publisher=Wadsworth, Cengage Learning |year=2011 |isbn=978-0-538-73465-3 |editor=Peggy Williams |edition=Twelfth |location=California |pages=100 |url-access=registration}}</ref>

The dehydration reaction that bonds monosaccharides into disaccharides (and also bonds monosaccharides into more complex [[polysaccharide]]s) forms what are called glycosidic bonds.<ref name="ochempal">{{cite web |title=Glycosidic Link |url=http://science.uvu.edu/ochem/index.php/alphabetical/g-h/glycosidic-link/ |archive-url=https://web.archive.org/web/20130512002153/http://science.uvu.edu/ochem/index.php/alphabetical/g-h/glycosidic-link/ |archive-date=May 12, 2013 |access-date=11 December 2013 |website=OChemPal |publisher=Utah Valley University}}</ref>

==Properties==
{{Unreferenced section|date=March 2023}}The glycosidic bond can be formed between any hydroxy group on the component monosaccharide. So, even if both component sugars are the same (e.g., glucose), different bond combinations (regiochemistry) and [[stereochemistry]] (''alpha-'' or ''beta-'') result in disaccharides that are [[diastereoisomer]]s with different chemical and physical properties. Depending on the monosaccharide constituents, disaccharides are sometimes crystalline, sometimes water-soluble, and sometimes sweet-tasting and sticky-feeling. Disaccharides can serve as [[functional group]]s by forming glycosidic bonds with other organic compounds, forming [[glycoside]]s.

==Assimilation==
{{See also|Carbohydrate digestion}}
Digestion of disaccharides involves breakdown into monosaccharides.

==Common disaccharides==
:{| class="wikitable"
|-
! Disaccharide
! Unit 1
! Unit 2
! Bond
|-
| [[Sucrose]] (table sugar, cane sugar, beet sugar, or saccharose)
| [[Glucose]] || [[Fructose]] || α(1→2)β
|-
| [[Lactose]] (milk sugar)
| [[Galactose]] || Glucose || β(1→4)
|-
| [[Maltose]] (malt sugar)
| Glucose || Glucose || α(1→4)
|-
| [[Trehalose]]
| Glucose || Glucose || α(1→1)α
|-
| [[Cellobiose]]
| Glucose || Glucose || β(1→4)
|-
| [[Chitobiose]]
| [[Glucosamine]] || Glucosamine || β(1→4)
|}

Maltose, cellobiose, and chitobiose are [[hydrolysis]] products of the polysaccharides [[starch]], [[cellulose]], and [[chitin]], respectively.

Less common disaccharides include:<ref>{{cite journal |author=Parrish |first1=F.W. |last2=Hahn |first2=W.B. |last3=Mandels |first3=G.R. |date=July 1968 |title=Crypticity of Myrothecium verrucaria Spores to Maltose and Induction of Transport by Maltulose, a Common Maltose Contaminant |url= |journal=J. Bacteriol. |publisher=American Society for Microbiology |volume=96 |issue=1 |pages=227–233 |doi=10.1128/JB.96.1.227-233.1968 |pmc=252277 |pmid=5690932 |doi-access=free}}</ref>

:{| class="wikitable"
|-
! Disaccharide
! Units
! Bond
|-
| [[Kojibiose]]  || Two [[glucose]]s || α(1→2)<ref>{{cite journal | last1 = Matsuda | first1 = K.  |date=November 1957 | title = Kojibiose (2-O-alpha-D-Glucopyranosyl-D-Glucose): Isolation and Structure: Chemical Synthesis | journal = Nature | volume = 180 | pages =985–6 | doi=10.1038/180985a0 | pmid = 13483573 | last2 = Abe | first2 = Y | last3 = Fujioka | first3 = K | issue = 4593 | bibcode = 1957Natur.180..985M | doi-access = free }}
</ref>
|-
| [[Nigerose]] || Two glucoses || α(1→3)
|-
| [[Isomaltose]] || Two glucoses || α(1→6)
|-
| β,β-Trehalose || Two glucoses || β(1→1)β
|-
| α,β-Trehalose || Two glucoses || α(1→1)β<ref>{{cite journal|journal=Acta Crystallogr. C|volume=53|pages=234–236|doi=10.1107/S0108270196012693|year=1997|author=T. Taga|author2=Y. Miwa|author3=Z. Min|title=α,β-Trehalose Monohydrate|issue=2}}</ref>
|-
| [[Sophorose]] || Two glucoses || β(1→2)
|-
| [[Laminaribiose]] || Two glucoses || β(1→3)
|-
| [[Gentiobiose]] || Two glucoses || β(1→6)
|-
| [[Trehalulose]]
| One glucose and one [[fructose]]
| α(1→1)
|-
| [[Turanose]] || One glucose and one fructose || α(1→3)
|-
| Maltulose || One glucose and one fructose || α(1→4)
|- 
| Leucrose || One glucose and one fructose || α(1→5)
|-
| [[Isomaltulose]] || One glucose and one fructose || α(1→6)
|-
| Gentiobiulose || One glucose and one fructose || β(1→6)
|-
| [[Mannobiose]] || Two [[mannose]]s || Either α(1→2), α(1→3), α(1→4), or α(1→6)
|-
| [[Melibiose]] || One [[galactose]] and one glucose || α(1→6)
|-
| [[Allolactose]] || One galactose and one glucose || β(1→6)
|-
| [[Melibiulose]] || One galactose and one fructose || α(1→6)
|-
| [[Lactulose]] || One galactose and one fructose || β(1→4)
|-
| [[Rutinose]] || One [[rhamnose]] and one glucose || α(1→6)
|-
| Rutinulose || One rhamnose and one fructose || β(1→6)
|-
| [[Xylobiose]] || Two xylopyranoses || β(1→4)
|}

==References==
{{Reflist}}

==External links==
*{{MeshName|Disaccharides}}

{{Sugar}}
{{Carbohydrates}}
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[[Category:Disaccharides| ]]
[[Category:Carbohydrate chemistry]]