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
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
Related conditions
Related
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).
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) (PubChem, NCBI, 2026) · Public domain; Fructose metabolism (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.