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Cellulose

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Cellose molecule.jpg

Cellulose is a insoluble complex carbohydrate (polysaccharide) formed from the products of photosynthesis, and is best known as dietary fiber or wood. It is the main component of the plant cell wall, and provides plants with structural integrity. It makes stems, stalks, and trunks rigid and therefore serves much the same function as the skeletal system in animals.

The best know use of this organic fiber is paper manufacturing. Papyrus is a type of paper produced as far back as 3000 BC from the papyrus plant, which was once abundant in the Nile river valley of Egypt.[1] It is also the raw material component used in the production of the manufactured fibers such as rayon, and is important in the manufacture of numerous products, such as pharmaceuticals and explosives.

Structure

Crystalline cellulose
Cellulose microfibril


Cellulose is an organic polymer composed of glucose monomers. It is a complex carbohydrate (polysaccharide) formed from monosaccharide subunits (glucose). The basic cellulose molecule contains alternating glucose residues in an inverted orientation. Pairs of these alternating glucose monomers form is the repeating structural unit called cellobiose (a disaccharide).[2]

It can be found in either a crystalline or fibrous structures with the chemical formula (C6H10O5)n.

Cell Wall

Main Article: Cell wall
Diagram of plant primary cell wall.

Cellulose in higher plants is organized into microfibrils, each measuring about 3 to 6 nm in diameter and containing up to 36 glucan chains having thousands of glucose residues. Like steel girders stabilizing a skyscraper’s structure, the primary cell-wall’s mechanical strength is due mainly to the microfibril scaffold. A microfibril’s crystalline and paracrystalline (amorphous) cellulose core is surrounded by hemicellulose, a branched polymer composed of pentose (5-carbon) and hexose (6-carbon) sugars. In addition to cross-linking individual microfibrils, hemicellulose in secondary cell walls (not shown) forms covalent associations with lignin, a rigid aromatic polymer whose structure and organization within the cell wall are poorly understood. The crystallinity of cellulose and its association with hemicellulose and lignin are two key challenges preventing efficient cellulose breakdown into glucose molecules.[3]

Cellulose Synthase Complexes

Many enzymes involved in cell-wall synthesis or modification are thought to be located in complexes. Within the plasma membrane are rosettes composed of the enzyme cellulose synthase; these protein complexes move through the membrane during the synthesis of glucan chains (36 per rosette) that aggregate to form cellulose microfibrils. Cellulose synthase interact with the cytoskeleton in a poorly characterized way impacting cellulose fibril orientation and perhaps length. Understanding the function of these complexes and their interactions with sugar-producing metabolic pathways will be important for eventually controlling cell-wall composition. A number of cellulose synthase genes have been cloned for a variety of plants.[4]

Metabolism

Enzymes such as cellulases synthesized by fungi and bacteria work together to degrade cellulose and other structural polysaccharides in biomass.[5]

References


See Also

Cellulose molecule showing glucose subunits