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monosaccharide
Monosaccharides (from Greek ''monos'': single, ''sacchar'': sugar; ''British English'': monosaccharides) are the most basic units of carbohydrates. They are fundamental units of carbohydrates and cannot be further hydrolised to simpler compounds. The general formula is where ''n'' is 1, 2, 3 ... . They are the simplest form of sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose (dextrose), fructose (levulose) and galactose. Monosaccharides are the building blocks of disaccharides (such as sucrose and lactose) and polysaccharides (such as cellulose and starch). Further, each carbon atom that supports a hydroxyl group (so, all of the carbons except for the primary and terminal carbon) is chiral, giving rise to a number of isomeric forms, all with the same chemical formula. For instance, galactose and glucose are both aldohexoses, but have different physical structures and chemical properties.
== Structure and nomenclature ==
With few exceptions (e.g., deoxyribose), monosaccharides have this chemical formula: C''x''(H2O)''y'', where conventionally ''x'' ≥ 3. Monosaccharides can be classified by the number ''x'' of carbon atoms they contain: diose (2) triose (3) tetrose (4), pentose (5), hexose (6), heptose (7), and so on.
The most important monosaccharide, glucose, is a hexose. Examples of heptoses include the ketoses mannoheptulose and sedoheptulose. Monosaccharides with eight or more carbons are rarely observed as they are quite unstable.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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