MONOSACCHARIDES

Monosaccharides are single-molecule sugars (the prefix “mono” means one) that form the basic units of carbohydrates. They usually consist of three to seven carbon atoms with attached hydroxyl (OH) groups in specific stereochemical configurations. The carbons of carbohydrates are traditionally numbered starting with the carbon of the carbonyl end of the chain (the carbonyl group is the carbon double-bonded to oxygen). The number of carbons in the molecule generally categorizes monosaccharides. For example, three-carbon carbohydrate molecules are called trioses, five-carbon moleculesare called pentoses, and six-carbon molecules are called hexoses.

Ribose and 2-deoxyribose are pentoses, and both have a crucial role in reproduction as polymers known as ribonucleic acid (RNA) and deoxyribonucleic acid
(DNA). One of the most important monosaccharides is glucose (dextrose). This molecule is the primary source of chemical energy for living systems. Plants and animals alike use this molecule for energy to carry out cellular processes. Mammals produce peptide hormones (insulin and glucagon) that regulate blood glucose levels, and a disease of high blood glucose is called diabetes. Other hexoses include fructose (found in fruit
juices) and galactose. Different structures are possible for the same monosaccharide. Although glucose and fructose are identical in chemical composition (C6H12O6), they are very different in structure (see molecular models). Such materials are called isomers. Isomers in general have very different physical properties based on their structure.