biological chemistry

Monosaccharides: Definition, Structure, Characteristics, Classification, Examples and Functions

Biochemistry of Monosaccharides

Chemical Structure, Characteristics, Examples & Classification

Monosaccharides are Simplest Sugars

Monosaccharides are the simplest carbohydrates. They are polyhydroxy aldehydes or ketones with a carbon backbone. The carbon backbone in monosaccharides usually consists of 3 – 6 carbon atoms. The simplest monosaccharides are glyceraldehyde and dihydroxyacetone (with 3 carbons). The most abundant monosaccharide in nature is a 6 carbon sugar called glucose. Majority of the monosaccharides follow the empirical formula C(H2O)n. Monosaccharide with five or more carbon can predominantly exist as cyclic structures in the aqueous condition. All monosaccharides are colourless, crystalline solids and that are readily soluble in water but insoluble in nonpolar solvents. Most of the monosaccharides are sweet in taste.

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Polyhydroxy aldehydes

Chemical Structure of Monosaccharides

Ø  All monosaccharides are polyhydroxy (contain many hydroxyl groups) aldehydes or ketones.

Ø  The hydroxyl groups are attached to the carbon backbone.

Ø  The number of carbon atoms in the backbone of monosaccharides varies from 3 to 6.

Ø  The carbon backbone of monosaccharides is unbranched and individual carbon atoms are connected by single bonds.

Ø  Monosaccharides are broadly classified into Aldoses and Ketoses.

Ø  In the open chain conformation of a monosaccharide, one of the carbon atoms of the backbone is double bonded to an oxygen atom to form the carbonyl group (C=O).

Ø  If the carbonyl group is at the end of the carbon chain it will be an aldehyde group (R – COH) and thus the sugar formed will be an Aldose sugar.

Ø  Similarly, if the carbonyl group is inner to the carbon chain, it will be a keto group (C=O) and the sugar formed will be a Ketose sugar.

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