Difference Between Cellulose and Hemicellulose

Main Difference – Cellulose vs Hemicellulose

Cellulose and hemicellulose are two types of polymers that serve as structural components of the plant cell wall. Both of them are polysaccharides. Thus, both cellulose and hemicellulose are made up of sugar monomers. Cellulose is produced by the polymerization of exclusively β-glucose monomers. In contrast, hemicellulose is made up of several monomers: xylose, galactose, mannose, rhamnose, and arabinose. Cellulose is a long polymer while hemicellulose is comparatively short. The main difference between cellulose and hemicellulose is that cellulose is a straight-chain polymer whereas hemicellulose is a cross-linked polymer.

Key Areas Covered

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

Key Terms: Cellulose, Glucose, Hemicellulose, Lignin, Microfiber, Pectin, Plant Cell wall, Polysaccharides

What is Cellulose

Cellulose refers to an inert carbohydrate, which is the main constituent of the plant cell wall. It is the most abundant macromolecule on earth. Though the chemical structure of cellulose mostly resembles glucose, it is extremely rigid, imparting a great strength to the plant and protecting the internal structures of the plant cell. Cellulose is a linear polymer made by the polymerization of beta-glucose molecules in a long chain. Each glucose molecule is upside down in relation to the neighboring glucose molecule. The structure of cellulose is shown in figure 1.

Figure 1: Cellulose

Cellulose is the third mass of a plant. The parallel aligned chains of cellulose produce microfibers; these microfibers are bound together by hydrogen bridges. The hydrogen bridges are formed by the hydroxyl groups of glucose molecules. Around 80 cellulose molecules are involved in the formation of a microfiber. Further cross-linking of fibers occurs through hemicellulose. The two types of fibers are suspended in a gel-like matrix made up of pectin that forms the middle lamella. The hydrogen bonds between linear cellulose molecules are shown in figure 2.

Figure 2: Hydrogen Bonds between Cellulose Molecules

As cellulose is the main component of the plant cell wall, it protects the plasma membrane of plant cells. Generally, cellulose can only be digested by the ruminant digestive system. There are few types of enzymes that are capable of hydrolyzing cellulose.

What is Hemicellulose

Hemicellulose refers to a constituent of the plant cell wall that consists of a simple structure than cellulose. It occupies 20 – 30% of the dry weight of wood. Hemicellulose consists of β-(1→4)-linked backbones. The types of monomers involved in the polymerization of hemicellulose are xylose, galactose, mannose, rhamnose, and arabinose. Hemicellulose cross-links with either cellulose or lignin, strengthening the cell wall. The biosynthesis of hemicellulose occurs in the Golgi apparatus under the influence of glycosyltransferases. The structure of the plant cell wall is shown in figure 3.

Figure 3: Plant Cell Wall

The composition of hemicellulose in softwood and hardwood differ from each other. The softwood mainly contains mannose, galactose, and lignin while the hardwood mainly consists of xylan and acetyl.

Similarities Between Cellulose and Hemicellulose

• Both cellulose and hemicellulose are polysaccharides made up of sugar monomers.
• Both cellulose and hemicellulose are structural components of the plant cell wall.

Difference Between Cellulose and Hemicellulose

Definition

Cellulose: Cellulose refers to an inert carbohydrate, which is the main constituent of the plant cell wall.

Hemicellulose: Hemicellulose refers to a constituent of the plant cell wall that consists of a simple structure than cellulose.

Significance

Cellulose: Cellulose is the long chain polymer in the plant cell wall.

Hemicellulose: Hemicellulose is the cross-linked polymer of the plant cell wall.

Type of Monomers

Cellulose: Cellulose is made by the polymerization of β-glucose.

Hemicellulose: Hemicellulose is made up of xylose, Galactose, mannose, rhamnose, and arabinose.

Physical Properties

Cellulose: Cellulose is a crystalline polymer and a strong polymer.

Hemicellulose: Hemicellulose has an amorphous polymer with little strength.

Abundance

Cellulose: Cellulose is the main structural component of the primary cell wall of plants.

Hemicellulose: Hemicellulose is present along with cellulose.

Hydrolysis

Cellulose: Cellulose is resistant to hydrolysis.

Hemicellulose: Hemicellulose is hydrolyzed easily by a dilute acid or base.

Length of the Polymer

Cellulose: Cellulose consists of long chains (7,000 – 15,000 sugar units).

Hemicellulose: Hemicellulose consists of short chains (500 – 3,000 sugar units).

Branching

Cellulose: Cellulose is an unbranched polymer.

Hemicellulose: Hemicellulose is a branched polymer.

Biosynthesis

Cellulose: Cellulose is synthesized by rosette terminal complexes (RTCs) at the plasma membrane.

Hemicellulose: Hemicellulose is synthesized from sugar nucleotides in the Golgi apparatus.

Digestion

Cellulose: Cellulose is only digestible by ruminants.

Hemicellulose: Hemicellulose can be easily digested by both humans and ruminants.

Importance

Cellulose: Cellulose can be used to produce paper, textiles, pharmaceuticals, and explosives. 

Hemicellulose: Hemicellulose can be used to produce paper, furfural, and ethanol. 

Conclusion

Cellulose and hemicellulose are two polysaccharides that serve as the structural components of the plant cell wall. Cellulose is made up of glucose monomers while hemicellulose is made up of several polymers. Cellulose is a linear polymer whereas hemicellulose is a cross-linked polymer. The main difference between cellulose and hemicellulose is the role of each polysaccharide in the plant cell wall.

Reference:

1. “Function of Cellulose in Plants.” Actforlibraries.org, Availabe here.
2. “Hemicelluloses.” Hemicelluloses | Annual Review of Plant Biology, Available here.

Image Courtesy:

1. “Cellulose Sessel” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
2. “Cellulose spacefilling model” By CeresVesta (talk) (Uploads) – Own work (Public Domain) via Commons Wikimedia
3. “Plant cell wall diagram-en” By LadyofHats – Own work (Public Domain) via Commons Wikimedia