Monosaccharides, Biology


  • Simple carbohydrate monomers, which cannot be hydrolysed further into simpler or smaller subunits.
  • Monosaccharides are generally colourless, crystalline and mostly sweet to taste.
  • The empirical formula is (CH2O)where n = 3 to 7.
  • A monosaccharide with aldehyde group is called aldose, generally having suffix as ose.
  • A monosaccharide with keto group is ketose, generally having suffix as ulose.





1. Trioses


2. Tetroses


3. Pentoses


4. Hexoses


5. Heptoses



Erythrose, Threose


Ribose, Deoxyribose, Xylose, Arabinose


Glucose, Galactose, Mannose


Glucoheptose, Galactoheptose

Dihydroxy acetone









1.       TRIOSES

  • The monosaccharides posses three carbons, e.g. Glyceraldehyde (an aldose) and Dihydroxy acetone (a ketose).
  • They are formed in both respiration and photosynthesis.

2.      TETROSES

  • The monosaccharides posses four carbons, e.g. Erythrose,Threose, Erythrulose.
  • Tetroses are intermediates of photosynthetic and respiratory pathways as well as raw materials for many biochemicals.
  • Erythrose is raw material for synthesis of anthocyanin & lignin.

3.       PENTOSES

  • They are with 5-carbon monosaccharides, e.g. Arabinose, Deoxyribose, Ribose, Ribulose, Xylose, Xylulose.
  • Deoxyribose is also a pentose sugar but has one oxygen atom less at 2nd C, formula is C5H10O4.It is component of DNA.
  • Ribose is raw material for synthesis of ribonucleotides, cAMP, ATP, NAD, NADP, FAD and RNA.
  • Ribose and Deoxyribose sugars are involved in formation of nucleotides.
  • Some pentose sugars are intermediates of photosynthetic and respiratory pathways.
  • Arabinose and xylose produce wall materials.
  • Arabinose present in gum of Accacia.
  • Ribulose present in RuBP.

4.       HEXOSES

  • They are six-carbon monosaccharides, e.g. Fructose, Galactose,Glucose, Mannose.
  • Fructose is fruit sugar but absent in grapes. It is also the sweetest of all natural sugars with sweetness index of 170. Also known as laevulose.
  • Glucose is blood sugar with a sweetness index of 70. It is raw material for formationof complex carbohydrates.
  • Glucose is the main respiratory substrate that is oxidised by every cell in order to obtain energy.
  • Glucose is reserve carbohydrates in grapes (Grape Sugar).
  • Gluscose is also known as dextrose.
  • Glucose present in the form of open chain or ring form.

2154_gluvose and fructose.png

  • Galactose does not occur freely but is a component of lactose, agar-agar, glycolipids and glycoproteins.
  • Galactose is milk sugar or brain sugar.
  • Galactose is fastly circulated in blood.
  • Mannose is found in cell wall and many prosthetic polysaccharides.
  • Mannose is also found in wood with component of hemicellulose.
  • Mannose is not found in free form.

5.       HEPTOSES

  • Heptoses are seven - carbon monosaccharides.
  • e.g., Glucoheptose, Galactoheptose, Sedoheptulose.
  • Sedoheptulose is intermediate of both photosynthetic and respiratory pathways.


Posted Date: 10/9/2012 3:17:32 AM | Location : United States

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