Question

How are carbohydrates classified?

Answer 1

There are several methods of classification, but the most common method is based on the number of sugar units they contain.

Explanation:

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

Functional Groups

• Aldoses — contain an aldehyde group, e.g. glucose
• Ketoses — contain a ketone group, e.g. fructose

Chemical Properties

• 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.

Structure

• Linear chains, e.g. amylose
• Branched chains, e.g. glycogen

Function

• Storage, e.g. starch, glycogen
• Structural, e.g. starch

Composition

• Homopolysaccharides — contain only single monosaccharide units, e.g. starch
• Heteropolysaccharides — contain different kinds of monosaccharides, e.g. hyaluronic acid (N-acetylglucosamine and glucuronic acid)