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How are glucose, fructose, and galactose alike?

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A biochemical flowchart shows the metabolic pathways for carbohydrate utilization, including glycolysis, the pentose phosphate pathway, and the tricarboxylic acid (TCA) cycle. The diagram traces the conversion of glucose, fructose, and glycerol through various intermediates, leading to energy production, carbon dioxide release, and biosynthesis of amino acids and porphyrins. Key steps and branches are labeled, with colored boxes highlighting biosynthetic outputs. — Carbohydrate Pathways for the utilization of carbohydrates.

Glucose, fructose, and galactose are alike in that they are all monosaccharides, or simple sugars.1

They share the same molecular formula, $C_{6} H_{12} O_{6}$ , which classifies them as hexoses because they each contain six carbon atoms. Because they possess the same chemical formula but differ in the structural arrangement of their atoms, these three sugars are isomers of one another.1

While they share this fundamental chemical composition, their distinct structural arrangements—specifically the positioning of their hydroxyl groups—result in different biological characteristics, such as varying degrees of sweetness.1