Cellulose is a hexose polysaccharide.
Cellulose [(C6H10O5)n] is a natural homopolymer and the main structural component of the plant cell wall. Cellulose is the most ubiquitously found organic molecule on earth. Microorganisms, algae, and plants synthesize cellulose fibers from glucose molecules (100s-1000s in numbers). French scientist Anselme Payen discovered the carbohydrate cellulose in 1838 and German Chemist Hermann Staudinger elucidate the chemical structure in 1920.
The glucose molecules are linked together by β(1→4)-glycosidic bonds to forms long cellulose fibers. About 100s to 1000s numbers of glucose molecules are linked together to form a glucose fiber. The enzyme cellulose synthase catalyzes the polymerization of glucose into cellulose fibers.
Cellulose is a water-insoluble polysaccharide. In the plant cells, cellulose is present in the form of fibrils. These fibrils are made up of microfibrils. Cellulose microfibrils consist of long parallel chains of glucose molecules. These polysaccharide chains are joined together by Hydrogen bonds in the microfibrils. These cellulose microfibrils are cementing together by a matrix mainly composed of polysaccharide pectin. This type of arrangement provides stability and high mechanical strength to plant cell walls.
Cellulase is the enzyme that breaks the β(1→4)-glycosidic bonds of cellulose. Due to the absence of cellulase enzyme, humans do not digest cellulose. Termites and herbivores also do not produce cellulase but they can able to digest cellulose due to the presence of gut microbes. The gut bacterium Ruminococcus flavefaciens in the ruminants mammals and the flagellated protists Trichonympha campanula produce cellulase enzyme and digests the cellulose.