Biochemistry · Molecule
Galactose !
Galactose is half of lactose, the sugar of milk; the liver turns it into glucose through the Leloir pathway.
Updated 2026-11-01
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Key facts
- An aldohexose (C₆H₁₂O₆), the carbon-4 epimer of glucose.
- It is absorbed alongside glucose through SGLT1 (with sodium) in the small intestine.
- It is part of glycolipids, glycoproteins, blood group antigens and breast-milk lactose.
- Formula
- C₆H₁₂O₆
- PubChem
- CID 439353
Structure
- Identical to glucose except the OH on carbon 4, which points the other way (the 3D model is β-D-galactopyranose).
Clinical notes
- Classic galactosaemia (GALT), galactokinase deficiency or epimerase deficiency.
- When it accumulates, aldose reductase turns it into galactitol: cataract.
Pathways
Related conditions
Related
Test yourself
Think of the answer, then tap the question to see it.
At which carbon do galactose and glucose differ?
At carbon 4: they are epimers.
Which disaccharide supplies dietary galactose?
Milk lactose (galactose + glucose).
Which galactose product causes cataract?
Galactitol, made by aldose reductase.
Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: beta-D-Galactopyranose (CID 439353) (PubChem, NCBI, 2026) · Public domain; Galactose catabolism (Reactome, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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Representative model, for educational purposes only.