A carbohydrate is a biological molecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water); in other words, with the empirical formula Cm(H2O)n (where m could be different from n). Some exceptions exist; for example, deoxyribose, a sugar component of DNA, has the empirical formula C5H10O4. Carbohydrates are technically hydrates of carbon; structurally it is more accurate to view them as polyhydroxy aldehydes and ketones.
The term is most common in biochemistry, where it is a synonym of 'saccharide', a group that includes sugars, starch, and cellulose. The saccharides are divided into four chemical groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Monosaccharides and disaccharides, the smallest (lower molecular weight) carbohydrates, are commonly referred to as sugars. The word saccharide comes from the Greek word σάκχαÏον (sákkharon), meaning "sugar". While the scientific nomenclature of carbohydrates is complex, the names of the monosaccharides and disaccharides very often end in the suffix -ose. For example, grape sugar is the monosaccharide glucose, cane sugar is the disaccharide sucrose, and milk sugar is the disaccharide lactose.
The major dietary carbohydrates
| Class (DP*) |
Subgroup |
Components |
|
Sugars (1–2) |
Monosaccharides |
Glucose, galactose, fructose, xylose
|
| Disaccharides |
Sucrose, lactose, maltose, trehalose
|
| Polyols |
Sorbitol, mannitol
|
|
Oligosaccharides (3–9) |
Malto-oligosaccharides |
Maltodextrins |
| Other oligosaccharides |
Raffinose, stachyose, fructo-oligosaccharides |
|
Polysaccharides (>9) |
Starch |
Amylose, amylopectin, modified starches |
| Non-starch polysaccharides |
Cellulose, hemicellulose, pectins, hydrocolloids
|
- Its monosaccharides: glucose and fructose
- Their ring types: glucose is a pyranose and fructose is a furanose
- How they are linked together: the oxygen on carbon number 1 (C1) of α-D-glucose is linked to the C2 of D-fructose.
- The -oside suffix indicates that the anomeric carbon of both monosaccharides participates in the glycosidic bond.
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