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Fructose (/ ˈ f r ʌ k t oʊ s,-oʊ z /), or fruit sugar, is a ketonic simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose.It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed by the gut directly into the blood of the portal vein during digestion.
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.
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 lipids in a process called ...
In 1897, an unfermentable product obtained by treatment of fructose with bases, in particular lead(II) hydroxide, was given the name glutose, a portmanteau of glucose and fructose, and was claimed to be a 3-ketohexose. [12] [13] However, subsequent studies showed that the substance was a mixture of various other compounds. [13] [14]
Haworth projection of the structures for α-D-glucopyranose and α-L-glucopyranose. 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.
Fructose, galactose, and glucose are all simple sugars, monosaccharides, with the general formula C 6 H 12 O 6. They have five hydroxyl groups (−OH) and a carbonyl group (C=O) and are cyclic when dissolved in water.
Right: a lactol of fructose, a cyclic hemiketal. Hemiacetals commonly exist in nature as aldoses such as glucose , and hemiketals commonly exist in nature as ketoses such as fructose . The favorability of the formation of a strain-free six-membered ring and the electrophilicity of an aldehyde combine to strongly favor the acetal form.
However, in order for anomers to exist, the sugar must be in its cyclic form, since in open-chain form, the anomeric carbon atom is planar and thus achiral. More formally stated, then, an anomer is an epimer at the hemiacetal/hemiketal carbon atom in a cyclic saccharide. [1] Anomerization is the process of conversion of one anomer to the other.