Monomer of Carbohydrates | Their Chemical Structure and Examples

Carbohydrates are optically active poly-alcoholic aldehydes or ketones.

They contain the elements carbon, hydrogen, and oxygen in the ratio 1:2:1.

These are biogenic and are found in both plants and animals.

Through food, one can avail large quantities of carbohydrates like sucrose, starch, cellulose, etc.

These carbohydrates are basically monomers and they form polymers to produce long chain and complex carbohydrates.

The monomers of carbohydrates are either formed due to the breakdown of complex carbohydrates or by the synthesis in the body.

What is the monomer of carbohydrates

A monomer is a basic carbohydrate molecule.

It can combine with similar units to form complex or bulk forms like polysaccharides, cellulose, starch, dimers, tetramers, glycogen, etc.

Examples of carbohydrate monomers

The carbohydrate monomers are classified based on the number of carbons in their chemical structure. These include

Three carbon monosaccharides

This group has only one monomer.

three-carbon monomer

Example: Glycerol

  • It is called glyceraldehyde.
  • This is the three-carbon carbohydrate that has an aldehyde group in its structure.

Since three carbons are present, it is also called triose sugar.

This monomer is naturally found in oils and fats as part of fatty acid ester.

It is a soft viscous liquid that has a mild sweet taste.

Four carbon monomers group

This group has two monomers which have 4 carbon atoms in its structure.

1. Erythrose

It is a 4 carbon monomer, i.e., a tetrose sugar.

Monomer of Carbohydrates

2. Threose

It is also 4 carbon monomer similar to erythrose in structure with a small variation.

threose a carbohydrate monomer

Five carbon carbohydrate monomers

Ribose sugar

  • It is a 5 carbon monomer.
  • A pentose sugar with many isomers.
  • It is found widely in the nucleic acids of living organisms.
  • It makes up the sugar part of RNA (Ribonucleic acids) and its deoxy form makes DNA.

So, ribose, a 5 carbon sugar, is one of the monomers of DNA and RNA.

arabinose


Example is Arabinose

  • It is 5 carbon saccharide is an aldopentose.
  • It is obtained from guar gum and also hydrolysis of vegetable matter.
  • It is sweet in taste and has two isoforms as below.
  • But (L) is available in plenty in nature.

Another example is Xylose

It is a five-carbon monomer obtained from wood.

It has two isomers and is an aldehyde, as in the image below.

Xylose

Another 5 carbon monomerLyxose

It is obtained from bacterial glycolipids. It is rarely available in nature.

Besides the above, there are also keto forms like ribulose, xylulose, etc.

Six carbon monomers

This group has monomers with carbons in them. These include 8 monomers like

1. Glucose

A 6 carbon carbohydrate and a hexose sugar. It is one of the most abundant carbohydrates and sweet in taste.

glucose a carbs monomer

2. Galactose

It is also 6 member carbohydrate.

It is a milk sugar as it is found more in dairy products.

It is also found in gums and mucilage.

galactose

3. Mannose

It is a carbohydrate that controls protein quality. It is formed in the body from glucose.

mannose

4. Altrose

It is a monomer found in a few bacteria.

altrose

5. Gulose

A 6 carbon monomer is found in bacteria, archaea, and few eukaryotes.

It is sweet in taste.

gulose

6. Talose

Another 6 member monomer, but it is unnatural.

talose
lyxose

8. Heptose: It is 7 member carbohydrate—heptose sugar.

Monomers of carbohydrates present in any sample can be identified by tests for carbohydrates.

References:
1. Lehninger principles of biochemistry.