Difference Between Chitin and Cellulose

The main difference between chitin and cellulose is that the chitin is a polymer of N-acetyl-D-glucosamine whereas the cellulose is a polymer of D-glucose. Furthermore, chitin occurs in the cell wall of fungi and also, it makes up the exoskeleton of arthropods while cellulose occurs in the cell wall of plants and algae. 

Chitin and cellulose are two polysaccharides made up of glucose-based polymers.  

Key Areas Covered 

1. What is Chitin
     – Definition, Structure, Function
2. What is Cellulose
     – Definition, Structure, Function
3. What are the Similarities Between Chitin and Cellulose
     – Outline of Common Features
4. What is the Difference Between Chitin and Cellulose
     – Comparison of Key Differences

Key Terms 

Cell Wall Components, Cellulose, Chitin, Polysaccharides, Strength

What is Chitin 

Chitin is the polysaccharide made up of N-acetyl-D-glucosamine monomers. The basic structure of chitin is similar to that of cellulose. The main function of chitin is to provide strength and support to the fungal cell wall. Moreover, chitin is the main structural component of the exoskeleton of arthropods such as insects and crustaceans. Chitin occurs in the radulae of mollusks, the beak of cephalopods, and the scales of fish as well. Chitin is used in the sizing and strengthening of paper and as a food thickener and stabilizer.

Figure 1: Chitin – Haworth Projection

The N-acetyl-D-glucose units form covalent β-(1→4)-linkages between them, creating a linear polymer. Cellulose will have the same structure as chitin when one of its hydroxyl group is replaced with the acetyl amine. The acetyl amine group increases the hydrogen bind formation capacity between adjacent polymers.  

What is Cellulose 

Cellulose is a polysaccharide made up of D-glucose monomers. It is the most abundant type of macromolecule on earth, making up of the plant and algal cell wall. Since the D-glucose monomers form β-(1→4)-linkages, cellulose is a linear polymer. The parallel-aligned polymers of cellulose form microfibers that are bound together by hydrogen bonds. There are around 80 cellulose molecules in a microfiber. These fibers are cross-linked with hemicellulose. Both cellulose and hemicellulose occur suspended in the middle lamella of the cell wall.

Figure 2: Hydrogen Bonding Between Cellulose Polymers

The main function of cellulose is to provide structural support to the plant cell and protection to the internal structures of the cell. 

Similarities Between Chitin and Cellulose 

• Chitin and cellulose are polysaccharides that occur in the cell wall of organisms. 
• They are biopolymers with glucose-based monomers. 
• Both are linked through covalent β-(1→4)-linkages. 
• They are insoluble in water. 
• Both form crystalline nanofibrils or whiskers.  
• The main function of chitin and cellulose is to provide structural support. 

Difference Between Chitin and Cellulose 

Definition 

Chitin refers to a fibrous substance consisting of polysaccharides, which is the major constituent in the exoskeleton of arthropods and the cell walls of fungi while cellulose refers to an insoluble substance, which is the main constituent of plant cell walls and of vegetable fibres such as cotton. 

Monomer Unit 

The monomer unit of chitin is N-acetyl-D-glucosamine while the monomer unit of cellulose is D-glucose. 

Nitrogen 

Chitin contains nitrogen while cellulose does not contain nitrogen. 

Functional Groups 

The second carbon of the glucose binds to an acetyl amine group in chitin while the second carbon of the glucose binds to a hydroxyl group in cellulose. 

Strength of the Polymer Matrix 

The strength of the chitin polymer matrix is higher due to the increased hydrogen bonding capacity while the strength of the cellulose polymer matrix is comparatively low. Therefore, chitin provides more rigidity to the structures than the cellulose does. 

Occurrence 

Chitin occurs in the cell wall of fungi and makes up the exoskeleton of arthropods while cellulose occurs in the cell wall of plants and algae. 

Evolution 

Chitin developed later and cellulose developed earlier. 

Abundance 

Chitin is comparatively less abundant and cellulose is the most abundant polysaccharide on earth.  

Conclusion 

Chitin is the structural component of the fungal cell wall and the exoskeleton of arthropods. Cellulose is the structural component of the plant and algal cell wall. The strength of chitin is higher than that of cellulose. The main difference between chitin and cellulose is the occurrence and strength of the molecules.

Reference:

1. “Chitin – Definition, Function, Structure and Examples.” Biology Dictionary, Biology Dictionary, 28 Apr. 2017, Available Here
2. “Cellulose.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 8 Feb. 2018, Available Here

Image Courtesy:

1. “Haworth projection of chitin” By Vaccinationist – Own work (Public Domain) via Commons Wikimedia    
2. “Cellulose spacefilling model” By CeresVesta (talk) (Uploads) – Own work (Public Domain) via Commons Wikimedia