saccharide

A saccharide is a sugar unit or carbohydrate molecule derived from the Greek word sakkharon. In biochemistry the term broadly covers monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Monosaccharides are the simplest units, while larger saccharides are built from them through glycosidic bonds. The term is often used to describe compounds that have the chemical formula and properties typical of sugars.

Saccharides are commonly classified by the number of monosaccharide units and by the presence of an aldehyde or ketone group. Monosaccharides include glucose, fructose, and galactose. Disaccharides such as sucrose, lactose, and maltose consist of two monosaccharides linked by a glycosidic bond. Oligosaccharides contain a few units, and polysaccharides such as starch, glycogen, and cellulose consist of many units. Monosaccharides may be further categorized as aldoses or ketoses, and as D- or L- isomers, with natural carbohydrates typically occurring in the D-configuration.

Chemically, saccharides can exist in linear or ring forms in solution. They form glycosidic bonds through dehydration synthesis and can be hydrolyzed by acids or specific enzymes. They are usually soluble in water, with properties influenced by the arrangement of hydroxyl groups. Reducing sugars include many monosaccharides and some disaccharides, while non-reducing sugars like sucrose lack a free anomeric carbon to reduce other reagents.

In biology, saccharides function as energy sources (glucose), energy stores (starch in plants, glycogen in animals), and structural components (cellulose in plants). They are also essential in nucleic acids (ribose, deoxyribose) and in cell signaling and recognition when linked to proteins and lipids.