Monomer of Carbohydrates | Their Chemical Structure and Examples

Carbohydrates are optically active poly-alcoholic aldehydes or ketones.

They contain 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 as sucrose, starch, cellulose etc.

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

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

What is the monomer of carbohydrates

A monomer is one which is a basic carbohydrate molecule. It can combine with other 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 which has as aldehyde group in its structure. Since three carbons are present, it is a triose sugar. It structure is

This is found in oils and fats as part of fatty acid ester. It is soft viscous liquid which 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 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 (Ribo nucleic acids) and its deoxy form makes DNA. Thus ribose a 5 carbob 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 a aldehyde.

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

Besides above there are also ketoforms like ribulose, xylulose etc.
Six carbon monomers: This group has monomers with carbons in them. These includes 8 monomers like

8. Glucose: A 6 carbon carbohydrate and a hexose sugar. It is one of the most abundant carbohydrate 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 few bacterium.

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

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

8. Heptose: It is 7 member carbohydrate. 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.
1. Lehninger principles of biochemistry.