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[Biochemistry](https://durgical.com/en/biochemistry/) · Molecule

# Fructose

Fructose is the sugar of fruit and honey, and half of table sugar; the liver handles almost all of it.

Updated 2026-11-01

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## Key facts

- A ketohexose (C₆H₁₂O₆), an isomer of glucose; sucrose is glucose + fructose.
- It is absorbed in the gut through GLUT5 (no sodium, no insulin) and leaves into the blood through GLUT2.
- In the liver: fructokinase → fructose 1-phosphate → aldolase B; it bypasses PFK-1.
- It is the sugar of semen (polyol pathway in the seminal vesicles): the sperm's energy source.

**Also called**
Levulose, Fruit sugar

**Formula**
C₆H₁₂O₆

**PubChem**
[CID 439709](https://pubchem.ncbi.nlm.nih.gov/compound/439709)

## Structure

- A ketose with the carbonyl on carbon 2; in sucrose and its phosphates it forms a five-membered furanose ring (the 3D model is β-D-fructofuranose).

## Clinical notes

- Hereditary fructose intolerance (aldolase B) and essential fructosuria (fructokinase).
- Absence of fructose in semen suggests obstruction or absence of the ejaculatory ducts or seminal vesicles.
- Excess added fructose favours fatty liver and high uric acid.

## Pathways

- [Fructose metabolism](https://durgical.com/en/biochemistry/pathways/fructose-metabolism/)

## Related conditions

- [Hereditary fructose intolerance](https://durgical.com/en/conditions/hereditary-fructose-intolerance/)
- [Essential fructosuria](https://durgical.com/en/conditions/essential-fructosuria/)
- [Gout](https://durgical.com/en/conditions/gout/)
- [Obesity](https://durgical.com/en/conditions/obesity/)

## Related

- [Glucose](https://durgical.com/en/biochemistry/molecules/glucose/)
- [Aldolase B](https://durgical.com/en/biochemistry/enzymes/aldolase-b/)
- [Galactose](https://durgical.com/en/biochemistry/molecules/galactose/)

## Test yourself

Think of the answer, then tap the question to see it.

## Through which transporter does fructose enter the enterocyte?

GLUT5, by facilitated diffusion without insulin.

## Which disaccharide contains fructose?

Sucrose (table sugar): glucose linked to fructose.

## What does absence of fructose in semen indicate?

A problem with the seminal vesicles or ejaculatory ducts (absence or obstruction).

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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-fructose (CID 439709)](https://pubchem.ncbi.nlm.nih.gov/compound/439709) (PubChem, NCBI, 2026) · Public domain; [Fructose metabolism](https://reactome.org/PathwayBrowser/#/R-HSA-5652084) (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/fructose/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/molecules/fructose/