Cellulose: Definition, Types, Structure, & Examples

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Cellulose Definition

(1) Cellulose is a polysaccharide made up of a β (1→4) linked linear chain of D-glucose units: (C6H10O5) n

(2) C6H10O5, a fibrous carbohydrate found in the cell walls of green plants, algae, and oomycetes. It gives plant cells their strength and rigidity.

What is Cellulose?

Cellulose is a polysaccharide carbohydrate that belongs to the category of carbohydrates known as polysaccharides. Carbohydrates are organic molecules that are made up of carbon, hydrogen, and oxygen in a 1:2:1 ratio.

Cellulose, What is Cellulose,

They belong to one of the most important groups of biomolecules. Carbohydrates made up of numerous saccharide units are known as polysaccharides. Some of them provide energy (for example, carbohydrates and glycogen), while others provide structural support (e.g. cellulose).

History of Cellulose

Anselme Payen (1795–1871), a French scientist, was the first to separate cellulose from plant materials in 1838. He also discovered cellulose’s chemical formula: (C6H10O5) n, where n denotes the degree of polymerization.

Cellulose Characteristics

Cellulose is odourless, tasteless, and biodegradable. It’s a carbohydrate polymer with a straight chain. It, like the other carbs, is a chemical substance. It consists of a linear chain of numerous glucose residues (300 to 1000 or more) connected by β(1→4) glycosidic bond.

The hydroxyl groups on one chain of glucose form hydrogen bonds with the oxygen atoms on another or the same chain of glucose. Between the chains, there are no glycosidic linkages. The hydrogen bonds that hold the chains side by side are what keep them together. As a result, cellulose emerges in the form of a microfibril.

It gives the cell wall tensile strength and functions as the plant’s “cytoskeleton.” The length of the chain or the degree of polymerization determine the other characteristics of cellulose.

Cellulose vs Starch

Cellulose is made up of multiple glucose monomers, comparable to starch. However, -glycosidic linkages connect the glucose residues in starch, i.e. α(1→4) in amylose and α-(1,4) and α(1→6) in amylopectin components.

Furthermore, cellulose is a monomer. It lacks the coiling and branching found in starch. Cellulose takes on a fairly stiff, rod-like shape. Plants biosynthesize both of these substances. Plants, on the other hand, use starch largely as a storage carbohydrate.

Plants generate cellulose primarily as a component of cell walls. Cellulose is a structural component of vascular plants’ main cell walls (as well as of many algae and oomycetes).

Cellulose vs Chitin

The most prevalent natural polysaccharide is cellulose, which is followed by chitin. Cellulose is a polysaccharide, similar to chitin, with monomers connected by β(1→4) glycosidic bonds. The monosaccharide components of cellulose and chitin differ: cellulose is a polymer of N-acetyl-D-glucosamine monomers, whereas chitin is a polymer of N-acetyl-D-glucosamine monomers.

Each monomer of chitin bears an acetylamine group instead of a hydroxyl group. This allows for greater hydrogen bonding between the polymers in chitin. As a result, chitin is a harder polysaccharide than cellulose, especially when coupled with calcium carbonate in a composite material.

Cellulose vs Hemicellulose

Another polymer found in plant cell walls is hemicellulose. Hemicellulose and cellulose are both polysaccharides, but hemicellulose is generated from more than just glucose polymerization. Xylose, galactose, mannose, rhamnose, and arabinose are also found in hemicellulose.

Hemicellulose is also a branched, cross-linked polymer, whereas cellulose is a straight-chain, unbranched polymer. They are also synthesised in different ways. While cellulose is made outside the cell (by the “rosette terminal complex” at the plasma membrane), hemicellulose is made inside the cell, in the Golgi apparatus, from sugar nucleotides.

Cellulose Synthesis

Aside from plants, cellulose is generated naturally by other species. Bacteria, protists, algae, and animals have all been found to produce it (e.g. tunicates). The earliest creature to generate cellulose is thought to be cyanobacteria.

Cellulose is generated outside the cell in higher plants, notably at the extracellular matrix or cell wall. The rosette terminal complex, a proteinaceous structure floating at the plasma membrane, produces it.

The cellulose synthases in the complex are involved in the production of the cellulose chain. Glucose is used as a precursor in the cellulose biosynthesis pathway. The following are the several steps in the path:

  • Glucose 6-phosphate (produced by hexokinase) from glucose
  • Glucose 6-phosphate (via phosphoglucomutase) Glucose 1-phosphate (via phosphoglucomutase)
  • UDP-glucose from glucose 1-phosphate (via UDP glucose pyrophosphorylase)
  • Glucan chains synthesized from UDP-glucose (via cellulose synthase)
  • Crystalline cellulose (crystallization process) Glucan chains

Cellulose chains are organised in the matrix like “cables.” Various glycoproteins and other polysaccharides are found in the matrix. A biofilm is made up of cellulose, which is generated by microorganisms. A biofilm is a microbial population that is held together by a polysaccharide, protein, and nucleic acid extracellular matrix.

Cellulose Degradation

Cellulolysis is the process of breaking down cellulose into cellodextrins and glucose units by hydrolysis. Many animals are unable to digest cellulose-rich foods. Ruminants, such as cows and sheep, can digest cellulose thanks to symbiotic anaerobic bacteria (such as Cellulomonas) that have cellulose-degrading enzymes. Cellulases are the enzymes in question.

The bacteria live in the hindgut, where they consume cellulose and digest it. Termites that feed on cellulose-rich wood can also digest it. In the hindgut of some of them, flagellate protozoans or microbial symbionts generate enzymes that may break glycosidic bonds. Cellulases are produced by other termites.

Biological Importance of Cellulose

Plant cell walls comprise cellulose, which is a key component. It helps to keep the cell wall stiff and strong. Animals which will digest cellulose may use this polysaccharide as a source of energy. Due to a lack of enzymes, humans are unable to digest cellulose. However, cellulose can still be included in the diet as a source of dietary fibre.

Cabbage, almonds, legumes, avocado, cherries, apples, pumpkin seeds, and other foods contain cellulose. It can also be chemically processed and used to make parmesan cheese, ice cream, and other commercial goods as a creaming agent or thickener. When eaten, the cellulose in these foods acts as an insoluble fibre, absorbing water and bulking up the stool.

When human microbiota are present in the large intestine, they can digest cellulose and produce short-chain fatty acids and gases.The body absorbs and metabolises the short-chain fatty acids.

Cellulose has a wide range of industrial uses. Cotton plants, for example, generate cotton fibres that contain more than 90% cellulose. Clothes, paper, rayon, cellophane, and construction materials can all be made from them. Biofuels have also been made using cellulosic material derived from energy crops (e.g. cellulosic ethanol).

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