Monosaccharides

Carbohydrates are major functional constituents of living system. Carbohydrates may be classified as monosaccharides, oligosaccharides, and polysaccharides.

Monosaccharides are simple carbohydrates containing between three and eight carbon atoms, but only those with six and five or six carbon atoms are common.

Monosaccharides consist of a single sugar molecule – mono meaning “one” and saccharide “sugar”.

Monosaccharides are often classified by both their number of carbon atoms and their functional group.

For example, an aldohexose is a monosaccharides that contains a total six carbon atoms including that of the aldehydes in its structure. Similarly, a ketopentose has five carbons in its structure including the one in the keto group.

Three of the most important ones in foods are the six carbon sugars glucose, fructose and galactose.

All the three monosaccharides have the same number and kinds of atoms but in different arrangements.

Glucose is known as an aldose sugar because it contains an aldehydes group (CHO) located on the first carbon atom of the chain.

Most cells depend on glucoses for their fuel to some extent, and the cells of the brain and the rest of the nervous system depend exclusively on glucose for their energy.

Fructose is a six carbon sugar, like glucose but it is a ketose sugar, not aldose , because it contains ketone group and not an aldehydes group.

Fructose occurs naturally in fruits, honey, and saps, Other source include soft drinks, ready to eat cereals and other products sweetened with high-fructose-corn-syrup.

Galactose rarely occurs as a monosaccharide in food. It usually chemically bonded to glucose to form lactose the primarily sugar in milk and dairy product.

During digestion galactose is freed as a simple sugar.

Monosaccharides are also often called sugar. Hexose are six-carbon sugars, pentoses five carbon sugar and so on. The word ‘sugar’ associated with ‘sweetness’ and most (but not all) monosaccharides, have a sweet taste.
Monosaccharides