How are D-glucose and D-fructose classified in relation to each other?

D-glucose and D-fructose are classified as structural isomers, meaning they have the same molecular formula but differ in the arrangement of their atoms and the way the atoms are connected to each other. Specifically, both of these sugars are hexoses, containing six carbon atoms, and they share the same chemical formula, C6H12O6. However, the arrangement of those carbon atoms varies.

In D-glucose, the carbonyl group (C=O) is located at the first carbon (making it an aldose), while in D-fructose, the carbonyl group is found at the second carbon (making it a ketose). This difference in the position of the carbonyl group is what distinguishes the two sugars' structures and leads to different chemical and physical properties.

Understanding this classification is important in biochemistry as it underscores the diverse roles that isomerism plays in metabolic processes and the functionality of biomolecules.