(C6H10O5)n. A structural polysaccharide found mainly in the cell walls of woody and fibrous plant material, such as cotton. It is a condensation polymer with glucose, and isomeric with starch. It is the main raw material for paper. Many important derivatives are formed by esterifying some of the hydroxyl groups; these include rayon (cellulose acetate) and guncotton (cellulose nitrate or nitrocellulose). Cellophane (a trade mark in some countries) is a form of cellulose which has been stretched into thin transparent sheets; it is used in the packaging of food and other perishable products.
The primary cell wall of green plants is made primarily of cellulose; the secondary wall contains cellulose with variable amounts of lignin. Lignin and cellulose, considered together, are termed lignocellulose, which (as wood) is argued to be one of the most common biopolymers on Earth (chrysolaminarin is often argued to be the other). Some acetic acid bacteria are also known to synthesize cellulose.Background
Cellulose is a common material in plant cell walls and was first noted as such in 1533.
Some animals, particularly ruminants and termites, can digest cellulose with the help of symbiotic micro-organisms - see methanogen. Cellulose is not digestible by humans, and is often referred to as 'dietary fiber' or 'roughage', acting as a hydrophilic bulking agent for faeces.
Cellulose is the major constituent of paper; Cellulose is used within the laboratory as a solid-state substrate for thin layer chromatography, and cotton linters, is used in the manufacture of nitrocellulose, historically used in smokeless gunpowder.
Rayon is a very important fiber made out of cellulose and has been used for textiles since the beginning of the 20th century.
Chemistry
Cellulose monomers (β-glucose) are linked together through ß1→4 glycosidic bonds by condensation. Cellulose is a straight chain polymer: unlike starch, no coiling occurs, and the molecule adopts an extended rod-like conformation.
In contrast to starch, cellulose is also much more crystalline. Whereas starch has an crystalline to amorphous transition at 60 -70 °C in water as in cooking, it takes 320°C and 25 MPa for cellulose to become amorphous in water .
Given a cellulose material, the portion that does not dissolve in a 17.5% solution of sodium hydroxide at 20 °C is α cellulose, which is true cellulose;
Cellulose can be assayed using a method described by Updegraff in 1969, where the fiber is dissolved in acetic and nitric acid, and allowed to react with anthrone in sulfuric acid.
Biosynthesis
Cellulose is synthesized in higher plants by enzyme complexes localized at the cell membrane called cellulose synthase. Cellulose synthase utilizes UDP-D-glucose precursors to generate microcrystalline cellulose. Cellulose synthesis requires chain initiation and elongation, and the two processes are separate.
Breakdown
The ability to breakdown cellulose is not possessed by mammals. The enzymes utilized to cleave the glycosidic linkage in cellulose are glycoside hydrolases including endo-acting cellulases and exo-acting glucosidases. Such enzymes are usually secreted as part of multienzyme complexes that may include dockerins and cellulose binding modules.
Derivatives
The hydroxyl groups of cellulose can be partially or fully reacted with various chemicals to provide derivates with useful properties. Cellulose esters and cellulose ethers are the most important commercial materials.
Among the esters are cellulose acetate and cellulose triacetate, which are film- and fiber-forming materials that find a variety of uses. Hydroxypropyl methyl cellulose, E464, used as a viscosity modifier, gelling agent, foaming agent and binding agent; Hydroxyethyl methyl cellulose, used in production of cellulose films.
Many cellulolytic bacteria break down cellulose into shorter linked chains known as cellodextrins.
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