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 ration 1:2:1.

These are biogenic and 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 monomer 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 one which is a basic carbohydrate molecule. It can combine with others to form more forms like polysaccharides, cellulose, starch, etc.

Three carbon monosaccharides: This group has only one monomer.

1. Glycerol: Also called as glyceraldehyde. This is the three-carbon carbohydrate that has an aldehyde group in its structure. Since three carbons are present, it is a triose sugar. Its structure is

This is 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 group: This group has two monomers as

2. Erythrose: It is a 4 carbon monomer i.e a tetrose sugar.

Monomer of Carbohydrates
3. Threose: It is also 4 carbon monomer similar to erythrose in structure with a small variation.

Five carbon carbohydrates:

4. Ribose: It is a 5 carbon monomer. A pentose sugar with many isomers. It is found widely in the nucleic acids of the living organisms. It makes up the sugar part of RNA (Ribonucleic acids) and its deoxy form makes DNA. Thus ribose a 5 carbon sugar is one of the monomers of DNA and RNA.
5. Arabinose: A 5 carbon saccharide which 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.

6. Xylose: It is a five-carbon monomer obtained from wood. It has two isomers and is an aldehyde.

7. Lyxose: Another 5 carbon monomer which is obtained from bacterial glycolipids. It is rarely available in nature


Besides 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

8. Glucose: A 6 carbon carbohydrate and a hexose sugar. It is one of the most abundant carbohydrates and sweet in taste.
9. 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.

10. Mannose: It is a carbohydrate which controls protein quality. It is formed in the body from glucose.


11. Altrose: It is a monomer found in a few bacteria.

12. Gulose: A 6 member monomer found in bacteria, archaea, and few eukaryotes. It is sweet in taste.

13. Talose: Another 6 member monomer but is unnatural.

8. Heptose: It is 7 member carbohydrates. A heptose sugar.

Monomers of carbohydrates present in any sample can be identified by tests for carbohydrates. The monomers combine to form dimers, tetramers and large polymers like starch, glycogen, cellulose, etc.
References:
1. Lehninger principles of biochemistry.