0.2 Bis2a 03.2 carbohydrates v1.2  (Page 54/19)

Carbohydrates

Molecular structures

Carbohydrates can be represented by the stoichiometric formula (CH ₂ O) _n , where n is the number of carbons in the molecule. In other words, the ratio of carbon to hydrogen to oxygen is 1:2:1 in carbohydrate molecules. This formula also explains the origin of the term “carbohydrate”: the components are carbon (“carbo”) and the components of water (hence, “hydrate”). Carbohydrates are classified into three subtypes: monosaccharides, disaccharides, and polysaccharides.

Nomenclature

One issue with carbohydrate chemistry is the nomenclature. Here are a few quick and simple rules:

1. Simple carbohydrates end with an "...ose"; such as glucose, lactose, or dexrose
2. Simple carbohydrates can be classified based on the number of carbon atoms in the sugar, such as a triose (3-carbons), pentose (5-carbons)or hexose (6-carbons).
3. Simple Carbohydrates can be classified based on the functional group found in the molecule, such as either a ketoses or aldoses
4. Polysaccharides are often organized by the number of sugar molecules in the chain, such as a monosaccharide, disaccharide or trisaccharide.

These will be explained in detail below. For a short video on carbohydrate classification see the Khan academy video (10 minutes in length) by clicking here .

Monosaccharides

Monosaccharides (mono- = “one”; sacchar- = “sweet”) are simple sugars, the most common of which is glucose. In monosaccharides, the number of carbons usually ranges from three to seven. Most monosaccharide names end with the suffix -ose. If the sugar has an aldehyde group (the functional group with the structure R-CHO), it is known as an aldose, and if it has a ketone group (the functional group with the structure RC(=O)R'), it is known as a ketose. Depending on the number of carbons in the sugar, they also may be known as trioses (three carbons), pentoses (five carbons), and or hexoses (six carbons). See [link] for an illustration of the monosaccharides.