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Glucose circulates in the blood of animals as blood sugar. [5] [7] The naturally occurring form is d-glucose, while its stereoisomer l-glucose is produced synthetically in comparatively small amounts and is less biologically active. [7] Glucose is a monosaccharide containing six carbon atoms and an aldehyde group, and is therefore an aldohexose ...
Reducing form of glucose (the aldehyde group is on the far right). A reducing sugar is any sugar that is capable of acting as a reducing agent. [1] In an alkaline solution, a reducing sugar forms some aldehyde or ketone, which allows it to act as a reducing agent, for example in Benedict's reagent.
The aldehyde group (or formyl group) is colored red. From the left: (1) formaldehyde and (2) its trimer 1,3,5-trioxane , (3) acetaldehyde and (4) its enol vinyl alcohol , (5) glucose (pyranose form as α- D -glucopyranose), (6) the flavorant cinnamaldehyde , (7) retinal , which forms with opsins photoreceptors , and (8) the vitamin pyridoxal .
Glucose can be the substrate in Kiliani–Fischer synthesis that adds a carbon to the aldehyde group and forms sugars with one more carbon than the substrate. The first step is nucleophilic addition of aqueous cyanide to aldehyde group in glucose to generate the cyanohydrin. Then cyanohydrin is hydrolyzed to form aldonic acid lactone upon heating.
The skeletal structure of an aldonic acid, gluconic acid (top), and its aldose, glucose (bottom). Aldonic acids are sugar acids with the general chemical formula, HO 2 C(CHOH) n CH 2 OH. They are obtained by oxidizing the aldehyde (-CHO group) of an aldose to form a carboxylic acid (-COOH group). [1] Aldonic acids are generally found in their ...
Thus, for example, the term "glucose" may signify glucofuranose, glucopyranose, the open-chain form, or a mixture of the three. Cyclization creates a new stereogenic center at the carbonyl-bearing carbon. The −OH group that replaces the carbonyl's oxygen may end up in two distinct positions relative to the ring's midplane.
An aldose is a monosaccharide (a simple sugar) with a carbon backbone chain with a carbonyl group on the endmost carbon atom, making it an aldehyde, and hydroxyl groups connected to all the other carbon atoms. Aldoses can be distinguished from ketoses, which have the carbonyl group away from the end of the molecule, and are therefore ketones.
Like glucose, maltose is a reducing sugar, because the ring of one of the two glucose units can open to present a free aldehyde group; the other one cannot because of the nature of the glycosidic bond. Maltose can be broken down to glucose by the maltase enzyme, which catalyses the hydrolysis of the glycosidic bond. [citation needed]