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How do aldose sugars differ from ketose sugars?

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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.

In biochemistry, monosaccharides are classified based on the position of their carbonyl group (C=O), which distinguishes aldose sugars from ketose sugars.1

Aldose Sugars: These contain an aldehyde group, which is located at the terminal carbon atom of the sugar chain. Because of this structural position, the aldehyde carbon is typically referred to as position 1.123
Ketose Sugars: These contain a ketone group, which is located at an internal position within the carbon chain, most commonly at the second carbon atom.21

This difference in the location of the carbonyl group influences the chemical properties and reactivity of the sugars. For example, aldoses and ketoses differ in their ability to form certain acid derivatives, such as the formation of specific aldonic acids. Additionally, because of their structural arrangements, ketose sugars possess one fewer asymmetrical center than aldose sugars for a given number of carbon atoms. In aqueous solutions, both types of sugars can form cyclic structures—hemiacetals for aldoses and hemiketals for ketoses—through the reaction of the carbonyl group with a hydroxyl group.4513