Difference Between Oligosaccharides and Polysaccharides

Main Difference – Oligosaccharides vs Polysaccharides

Oligosaccharides and polysaccharides are carbohydrates. These carbohydrates play a major role in nutrition and act as structural components of living organisms. Both oligosaccharides and polysaccharides are made of simple sugar molecules called monosaccharides. The main difference between oligosaccharides and polysaccharides is that oligosaccharides are made out of a few number of monosaccharides whereas polysaccharides are made out of a large number of monosaccharides.

Key Areas Covered

1. What are Oligosaccharides
      – Definition, Properties, Examples
2. What are Polysaccharides
      – Definition, Properties, Examples
3. What are the Similarities Between Oligosaccharides and Polysaccharides
      – Outline of Common Features
4. What is the Difference Between Oligosaccharides and Polysaccharides
      – Comparison of Key Differences

Key Terms: Carbohydrates, CH₂O, Empirical Formula, Glycosidic Bond, Monosaccharides, Oligosaccharides, Polysaccharides

What are Oligosaccharides

Oligosaccharides are carbohydrates composed of a few number of monosaccharide units. A monosaccharide is a simple sugar, having the empirical formula CH₂O. The number of monosaccharides present in an oligosaccharide varies from 3 to 6. In rare occasions, oligosaccharides having about 10 monosaccharides are also found. The bond between two monosaccharides is called a glycosidic bond. It is a covalent bond that formed through a condensation reaction. This bond occurs between a carbon atom of one sugar molecule and the oxygen atom of the hydroxyl group (-OH) of another sugar molecule. This condensation polymerization results in a water molecule (H₂O) per every glycosidic bond, as a byproduct.

Oligosaccharides are water soluble carbohydrates since their structure is not that much complex. Oligosaccharides taste are sugars and taste sweet. Most of the oligosaccharides act as transport molecules, but they are not storage molecules.

Main Difference - Oligosaccharides vs Polysaccharides

Figure 1: Structure of Raffinose

Examples for Oligosaccharides

Oligosaccharide	Number of Monosaccharides	Types of Monosaccharides	Occurrence
Raffinose	three	Glucose, Galactose, Fructose	Vegetables and whole grains
Stachyose	Four	Glucose, two Galactose, Fructose	Vegetables

What are Polysaccharides

Polysaccharides are large molecules composed of a large number of monosaccharides. These monosaccharides are linked via glycosidic bonds. Typically, a polysaccharide is composed of about 200 monosaccharides. These monosaccharides are connected to each other either as a linear chain or as a branched structure. The formation of a polysaccharide occurs through condensation polymerization.

Most of the polysaccharides act as structural carbohydrates and energy storing carbohydrates. Therefore, cellulose is the most abundant organic molecule on earth. Polysaccharides do not taste sweet and are non-reducing molecules. Almost all polysaccharides are insoluble in water.

Difference Between Oligosaccharides and Polysaccharides

Figure 2: Complex Structure of Glycogen

Examples of Polysaccharides

Polysaccharide	Types of Monosaccharides present	Uses
Starch	Glucose	Energy storage in plants
Glycogen	Glucose	Energy storage in animals
Cellulose	Glucose	Structural component of plant cell wall

Similarities Between Oligosaccharides and Polysaccharides

Oligosaccharides and polysaccharides are carbohydrates.
They are essentially composed of C, H and O atoms
Both are made out of monosaccharide units
Glycosidic bonds are present in both types.

Definition

Oligosaccharides: Oligosaccharides are carbohydrates composed of a few number of monosaccharide units.

Polysaccharides: Polysaccharides are large molecules composed of a large number of monosaccharides.

Number of Monosaccharides

Oligosaccharides: Oligosaccharides are composed of 2 to 6 (rarely 10) monosaccharides.

Polysaccharides: Polysaccharides are composed of about 200 monosaccharides.

Function

Oligosaccharides: Oligosaccharides act as transport molecules.

Polysaccharides: Polysaccharides act as structural or energy storage molecules.

Water Solubility

Oligosaccharides: Oligosaccharides are water soluble.

Polysaccharides: Polysaccharides are water insoluble.

Taste

Oligosaccharides: Oligosaccharides tastes sweet.

Polysaccharides: Polysaccharides do not taste sweet.

Conclusion

Although oligosaccharides and polysaccharides fall into the same carbohydrate category, there are some distinct features among them. The main difference between oligosaccharides and polysaccharides is their composition; oligosaccharides are made out of a few number of monosaccharides whereas polysaccharides are made out of a large number of monosaccharides.

Image Courtesy:

1. “Raffinose” By Yikrazuul – Own work; ISBN 978-3540737322, S. 390, Public Domain) via Commons Wikimedia
2. “Glycogen structure” – “Medical gallery of Mikael Häggström 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.008. ISSN 2002-4436. (Public Domain) via Commons Wikimedia

References:

1.”Polysaccharides.” Study.com. Study.com, n.d. Web. Available here. 29 June 2017.
2.”Oligosaccharides.” Chemistry LibreTexts. Libretexts, 11 Mar. 2017. Web. Available here. 29 June 2017.