Isomers

Glucose, galactose and fructose are isomeric monosaccharides (hexoses), meaning they have the same chemical formula but have slightly different structures. Glucose and galactose are aldoses, and fructose is a ketose. By convention, the carbon atoms in a monosaccharide are numbered from the terminal carbon closest to the carbonyl group. Monosaccharides can exist as a linear chain or as ring-shaped molecules..

Chemical structures of glucose, galactose and fructose. Each structure has a 6 carbon backbone. Glucose has a double bonded oxygen on C1 and an O H group to the right of C4. Galactose has a double bonded oxygen to C1 and an O H group to the left of C4. Fructose has a double bonded oxygen on C2 and an O H group on C1.

Figure 1: Chemical structure isomerism of glucose, galactose and fructose.

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Monosaccharides