Editing Reducing sugar (section)

==Terminology==

===Oxidation-reduction===
A ''reducing sugar'' is one that ''reduces'' another [[Chemical compound|compound]] and is itself ''[[Redox|oxidized]]''; that is, the [[Carbonyl group|carbonyl]] carbon of the [[sugar]] is oxidized to a [[carboxyl]] group.<ref name=Lehninger>{{cite book |last1=Nelson |first1=David L. |last2=Cox |first2=Michael M. |date=2008 |title=Lehnniger: Principles of Biochemistry |publisher=W.H. Freeman and Company |edition=Fifth |page=[https://archive.org/details/lehningerprincip00lehn_1/page/241 241] |isbn=978-0716771081 |url-access=registration |url=https://archive.org/details/lehningerprincip00lehn_1/page/241 }}</ref>

A sugar is classified as a reducing sugar only if it has an [[open-chain]] form with an aldehyde group or a free [[hemiacetal]] group.<ref name=Campbell>{{cite book |last1=Campbell |first1=Mary K. |last2=Farrell |first2=Shawn O.  |date=2012 |title=Biochemistry |publisher=Cengage Learning |page=459 |isbn=978-0840068583}}</ref>

===Aldoses and ketoses===
[[Monosaccharide]]s which contain an aldehyde group are known as [[aldoses]], and those with a ketone group are known as [[ketoses]]. The aldehyde can be oxidized via a [[redox reaction]] in which another compound is reduced. Thus, aldoses are reducing sugars. Sugars with [[ketone]] groups in their open chain form are capable of isomerizing via a series of [[tautomerism|tautomeric]] shifts to produce an aldehyde group in solution. Therefore, ketones like [[fructose]] are considered reducing sugars but it is the isomer containing an aldehyde group which is reducing since ketones cannot be oxidized without decomposition of the sugar. This type of isomerization is catalyzed by the base present in solutions which test for the presence of reducing sugars.<ref name=Campbell/>

===Reducing end===
Disaccharides consist of two monosaccharides and may be either reducing or nonreducing. Even a reducing disaccharide will only have one reducing end, as disaccharides are held together by [[glycosidic bond]]s, which consist of at least one [[anomeric carbon]]. With one anomeric carbon unable to convert to the open-chain form, only the free anomeric carbon is available to reduce another compound, and it is called the ''reducing end'' of the disaccharide. 
A nonreducing disaccharide is that which has both anomeric carbons tied up in the glycosidic bond.<ref>{{cite book |last1=Nelson |first1=David L. |last2=Cox |first2=Michael M. |date=2008 |title=Lehnniger: Principles of Biochemistry |publisher=W.H. Freeman and Company |edition=Fifth |page=[https://archive.org/details/lehningerprincip00lehn_1/page/243 243] |isbn=978-0716771081 |url-access=registration |url=https://archive.org/details/lehningerprincip00lehn_1/page/243 }}</ref>

Similarly, most polysaccharides have only one reducing end.