Cellulose Digestion: Characteristic and Process

Cellulose digestion or breakdown of cellulose is usually seen in plants while higher animals and humans lack the necessary enzymes to digest it. cellulose is a significant component of a plant cell wall, made of complex carbohydrates. However, many animals, particularly herbivores, have evolved specialized digestive systems that allow them to obtain nutrients from plant-based foods that contain cellulose

Read More: Digestion and Absorption

Keywords: Cellulose, Cellulose digestion, Ruminants, Enzyme, Glucose, Digestion

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What is Cellulose?

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Cellulose is thought to be the most widely available organic compound on the planet, made up of a linear chain (14) linked D-glucose units: (C6H10O5)n. Polysaccharides are carbohydrates composed of multiple saccharide units. Some are energy fuels (for example, starch and glycogen), while others have structural functions (e.g. cellulose). It is a fibrous carbohydrate found in the cell walls of green plants, algae, and oomycetes. Plant cells benefit from their strength and rigidity.

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Characteristics of Cellulose

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Characteristics of cellulose is as follows;

• Cellulose is biodegradable, odorless, and tasteless.
• It is a straight-chain carbohydrate polymer. 
• It is an organic compound composed of a linear chain of multiple glucose residues (300 to 1000 or more units) linked by a (14) glycosidic bond.
• Glucose from one chain form hydrogen bonds with the oxygen atoms on the glucose from another or the same chain.
• There are no glycosidic bonds between the chains.
• The hydrogen bonds that hold the chains together are what keeps them together.
• As a result, cellulose appears as a microfibril. 
• It provides tensile strength to the cell wall, which serves as the "cytoskeleton" of the plant.
• Other cellulose properties are determined by the chain length or the degree of polymerization.

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Digestion of cellulose

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Cellulose is a complex carbohydrate found in the cell walls of plants. While it is an essential source of nutrition for many herbivorous animals, it is not readily digestible by most animals because they lack the necessary enzymes to break it down.

Ruminants, For instance, animals like cows, sheep, and deer, have unique digestive systems that enable them to digest cellulose. The process of cellulose digestion in these animals begins in the rumen, a large fermentation chamber located in the front part of their stomach.

Microorganisms such as bacteria, protozoa, and fungi that produce enzymes capable of breaking down cellulose break it down in the rumen. These microorganisms are symbiotic with the ruminant because they give a warm, moist environment and a steady food supply. The ruminant benefits from the microorganisms' ability to digest cellulose.

The process of cellulose digestion in animals (Ruminants) generally involves the following steps:

1. Ingestion

Animals consume plant-based foods that contain cellulose, such as grasses, leaves, and stems.

2. Mechanical breakdown

The food is mechanically broken down in the mouth and stomach through chewing and grinding. This increases the surface area of the food, making it easier to digest.

3. Enzymatic breakdown 

In the rumen and reticulum of ruminants (such as cows and sheep), cellulose is broken down by microorganisms such as bacteria and protozoa that produce cellulase enzymes.

4. Fermentation

As cellulose is broken down, it produces volatile fatty acids (VFAs) absorbed in the stomach and small intestine. In ruminants, VFAs are absorbed in the rumen and reticulum.

5. Absorption 

The nutrients and VFAs produced by cellulose digestion are absorbed through the small intestine walls and sent to the liver, where they are used for energy or preserved for later use.

Overall, the process of cellulose digestion in animals is a complex and multi-step process that requires the involvement of specialized microbes and enzymes.

• Non-ruminant animals, such as rodents and rabbits, have a specialized portion of their digestive system called the cecum.
• It allows them to ferment and digest cellulose using bacteria and other microorganisms.
• The process is similar to ruminants but occurs in a different part of the digestive tract.
• Termites are another example of animals that can digest cellulose. 
• These insects have evolved a symbiotic relationship with microbes that live in their gut.
• The microbes produce enzymes that break down cellulose into glucose.
• Termites use it as their primary energy source.

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Why Can't Humans Digest Cellulose?

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In contrast to herbivorous animals and termites, cellulose cannot be digested in the human body without appropriate enzymes to break the beta-acetal linkages. 

• The human body lacks the digestive mechanism to break cellulose bonds.
• Although cellulose is indigestible, it aids in the smooth functioning of the intestinal tract.
• It plays an essential role in the human body because it is an excellent source of fiber. 

However, some researchers have suggested that certain microbes in the human gut, such as bacteria in the genus Bacteroides, may be able to break down cellulose to some extent, providing additional nutrients for the host.

Read More: Auxins

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Things To Remember

• Cellulose is a complex carbohydrate.
• It is present in plants and they can easily digest it
• It is highly resistant to digestion in most animals, including humans.
• However, some animals, such as herbivores and termites can digest it.
• Cellulose provides tensile strength to the cell wall.
• It serves as a cytoskeletal component.
• It is a linear chain of glucose molecules bonded to each other with glycosidic bonds.