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[Biochemistry](https://durgical.com/en/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

Loading the 3D model…

## 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](https://pubchem.ncbi.nlm.nih.gov/compound/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

- [Galactose metabolism](https://durgical.com/en/biochemistry/pathways/galactose-metabolism/)
- [Lysosomal ganglioside breakdown](https://durgical.com/en/biochemistry/pathways/lysosomal-ganglioside-breakdown/)

## Related conditions

- [Classic galactosaemia](https://durgical.com/en/conditions/classic-galactosaemia/)
- [Lactose intolerance](https://durgical.com/en/conditions/lactose-intolerance/)
- [Cataract](https://durgical.com/en/conditions/cataract/)

## Related

- [Glucose](https://durgical.com/en/biochemistry/molecules/glucose/)
- [UDP-glucose](https://durgical.com/en/biochemistry/molecules/udp-glucose/)
- [Galactose-1-phosphate uridylyltransferase (GALT)](https://durgical.com/en/biochemistry/enzymes/galactose-1-phosphate-uridylyltransferase/)
- [Fructose](https://durgical.com/en/biochemistry/molecules/fructose/)

## 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.

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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)](https://pubchem.ncbi.nlm.nih.gov/compound/439353) (PubChem, NCBI, 2026) · Public domain; [Galactose catabolism](https://reactome.org/PathwayBrowser/#/R-HSA-70370) (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.

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Source: https://durgical.com/en/biochemistry/molecules/galactose/
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