Carbohydrates
CarbohydratesThere are three principal kinds of carbohydrates and each are classified according to the number of sugar molecules they contain. Monosaccharides, such as ribose, glucose, and fructose, contain only one sugar molecule. Disaccharides consist of two sugar molecules linked covalently. Familiar examples are sucrose (table sugar), maltose (malt sugar), and lactose (milk sugar). Polysaccharides, such as cellulose and starch, contain many sugar molecules linked together.
Monosaccharides are organic compounds composed of carbon, hydrogen, and oxygen. They can be described by the chemical formula (CH2O)n, where n may be as small as 3 or as large as 8. They are characterized by hydroxyl groups and an aldehyde or ketone group. These functional groups make sugars highly soluble in aqueous solution. In solution the aldehyde or ketone group has a tendency to react with one of the hydroxyl groups, producing a ring structure. The alpha glucose, which is the base of many polymers, is an energy source in organisms.
Although glucose is the common transport sugar for vertebrates, sugars are often transported in other organisms as disaccharides. Sucrose, commonly called cane sugar, is the form in which sugar is transported in plants from the...
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