How are carbohydrates classified?
There are several methods of classification, but the most common method is based on the number of sugar units they contain.
Number of Sugar Units
- Monosaccharides — 1 unit, e.g. glucose
- Oligosaccharides —2 to 9 units
o Disaccharides — 2 units, e.g. sucrose
- Polysaccharides — ≥ 10 units, e.g., starch
Other methods of classification include:
Number of Carbon Atoms
- 5 = pentose, e.g. ribose
- 6 = hexose, e.g., glucose
- Aldoses — contain an aldehyde group, e.g. glucose
- Ketoses — contain a ketone group, e.g. fructose
- Reducing — react with Fehling's solution or Tollens' reagent, e.g. glucose, lactose
- Non-reducing — no reaction with Fehling's solution or Tollens' reagent, e.g. sucrose, all polysaccharides
Polysaccharides have other classifications.
- Linear chains, e.g. amylose
- Branched chains, e.g. glycogen
- Storage, e.g. starch, glycogen
- Structural, e.g. starch
- Homopolysaccharides — contain only single monosaccharide units, e.g. starch
- Heteropolysaccharides — contain different kinds of monosaccharides, e.g. hyaluronic acid (N-acetylglucosamine and glucuronic acid)