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For many monosaccharides (including glucose), the cyclic forms predominate, in the solid state and in solutions, and therefore the same name commonly is used for the open- and closed-chain isomers. Thus, for example, the term "glucose" may signify glucofuranose, glucopyranose, the open-chain form, or a mixture of the three.
Monosaccharides are classified according to three different characteristics: the placement of its carbonyl group, the number of carbon atoms it contains, and its chiral handedness. If the carbonyl group is an aldehyde, the monosaccharide is an aldose; if the carbonyl group is a ketone, the monosaccharide is a ketose.
[1] [2] The simplest ketose is dihydroxyacetone ((CH 2 OH) 2 C=O), which has only three carbon atoms. It is the only ketose with no optical activity . All monosaccharide ketoses are reducing sugars , because they can tautomerize into aldoses via an enediol intermediate, and the resulting aldehyde group can be oxidised , for example in the ...
Another nomenclature uses the systematic name of the molecular graph, a ' D-' or ' L-' prefix to indicate the position of the last chiral hydroxyl on the Fischer diagram (as above), and another italic prefix to indicate the positions of the remaining hydroxyls relative to the first one, read from bottom to top in the diagram, skipping the keto ...
Presumably, glucose is the most abundant natural monosaccharide because it is less glycated with proteins than other monosaccharides. [64] [65] Another hypothesis is that glucose, being the only d-aldohexose that has all five hydroxy substituents in the equatorial position in the form of β-d-glucose, is more readily accessible to chemical ...
Another important disaccharide is lactose found in milk, consisting of a glucose molecule and a galactose molecule. Lactose may be hydrolysed by lactase, and deficiency in this enzyme results in lactose intolerance. When a few (around three to six) monosaccharides are joined, it is called an oligosaccharide (oligo-meaning "few").
An oligosaccharide has both a reducing and a non-reducing end. The reducing end of an oligosaccharide is the monosaccharide residue with hemiacetal functionality, thereby capable of reducing the Tollens’ reagent, while the non-reducing end is the monosaccharide residue in acetal form, thus incapable of reducing the Tollens’ reagent. [2]
Like some other monosaccharides, pentoses exist in two forms, open-chain (linear) or closed-chain (cyclic), that easily convert into each other in water solutions. [3] The linear form of a pentose, which usually exists only in solutions, has an open-chain backbone of five carbons.