They are carbohydrates made up of chains of five carbon atoms.
The aldopentoses have three asymmetric carbons (C2 ,C3 and C4), so there are eight possible molecular structures (23 = 8). Only four are found in nature:
- D-ribose, in ribonucleic acid .
- D-2 -deoxyribose, in deoxyribonucleic acid .
- D-xylose, a component of the wood xylan polysaccharide .
- L-arabinose, forming the polysaccharide arabana , which is one of the components of gum arabic.
Among the ketopentoses, mention should be made of D-ribulose, which plays a fundamental role in photosynthesis, since it binds to the carbon dioxide (CO2) molecule, introducing it into organic matter.