Cellulose in plant cell walls

Hemicelluloses repr s ni a class of noncellulosic polysaccharides that is associated with cellulose in plant cell walls [56]. The term hemicelluloses was first used by Schulze in 1887 in the belief that (hemi- or half)-celluloses were perhaps components that were on the way of becoming cellulose a term meant to distinguish this group of noncellulosic polysaccharides from that which makes up the cell wall stmcture. It has long been recognized that the term is unfortunate and misleading, and that polyoses or heteropolysaccharides are better descriptors [57]. However, hemicelluloses is an often-used designation for the noncellulosic heteropolysaccharide components in plants. The latter term shall be used in this text. 

In an analogous way to collagen In mammalian connective tissues and cellulose In plant cell walls. All of these tissues can be classified as fiber-matrix composites in the cell walls of higher plants the cellulose fibrils are surrounded by other polysaccharides, proteins, and also lignin In some cases In... 

Hemicellulose, which is a highly branched polysaccharide in contrast to linear cellulose, is located attached to the cellulose in plant cell walls. Hemicellulose, such as ara-binoxylans, is not a form of cellulose but is another group of polysaccharides [3]. Being... 

Callose is an amorphous -(1 3) glucan accompanying cellulose in plant cells walls, but it is less common than cellulose. Most plants synthesise this polysaccharide in response to injury or only at certain stages of development of cell walls. The basic building unit of callose is disaccharide laminaribiose, (S-D-glucopyranosyl-(1 3)-D-glucopyranose (4-149). 

Xylans are a group of polymers based on a structure analogous to that of cellulose wherein xylose is the repeating unit. The simplest representative contains only D-xylose with /3-1-4 linkages and is a common component of plant walls. Several heteropolysaccharides utilize the xylan backbone and have various other saccharides as branches. Xylans are often associated with cellulose in plant cell walls. 

Source Adapted from various sources including (i) Wood chemistry , E. Sjostrom, 2nd edition, 1993, p. 52 (ii) Cellulose Biosynthesis , D.F. Delmer, Ann. Rev. Plant Physiol., 1987, 38, 259-290 (iii) Biosynthesis in Plant Cell Walls , D.F. Delmer, in The Biochemistry of Plants , vol. 14, Academic Press, San Diego, 1988, pp. 373-420). 

The largest and most complex carbohydrates are the polysaccharides. They are polymers, long chains of repeating chemical units. Each individual unit is called a monomer. The monomer unit of polysaccharides is the monosaccharide, normally glucose. A typical polysaccharide contains several hundred individual monomers. Examples of common polysaccharides are starches, plant products that are major macronutrients in the human diet, and cellulose, found in plant cell walls. In the human diet, cellulose is referred to as fiber, indigestible but beneficial for normal intestinal motility. More than half of the Earth s total carbon is stored in these two polysaccharides. 

Cellulose is reputedly the most abundant organic material on Earth, being the main constituent in plant cell walls. It is composed of glucopyranose units linked pi 4 in a linear chain. Alternate residues are rotated in the structure, allowing hydrogen bonding between adjacent molecules, and construction of the strong fibres characteristic of cellulose, as for example in cotton. 

Lignin is found in plant cell walls of supporting and conducting tissue, mostly the trac-heids and vessel parts of the xylem. It is largely found in the thickened secondary wall but can occur elsewhere close to the celluloses and hemicelluloses. 

Newman, R. H., Davies, L. M., Harris, P. J. (1996). Solid-state C nuclear magnetic resonance characterization of cellulose in the cell walls of Arabidopsis thaliana leaves. Plant Physiol, III, 475 85. 

Fred s courage, and his capability to delve into multidisciplinary problems involving a range of subjects from physical chemistry to cellular biology, are clearly reflected in his penetrating analysis and discussion in an article on the morphology and biogenesis of cellulose and plant cell-walls. This article unfolded more than a century of multidisciplinary developments in a critical and coherent manner that constituted a hallmark in cellulose... 

Dietary Fiber. Dietary fiber is a broad term that encompasses the indigestible carbohydrate and carbohydrate-like components of foods that are found predominantly in plant cell walls (see Carbohydrates). It includes cellulose lignin, hemicelluloses. pentosans, gums, and pectins. 

There are other polysaccharides besides cellulose in the cell walls of plants. These are called hemicelluloses, but the name is misleading because they are unrelated to cellulose. Those that are made of pentose units (mainly xylose) are most abundant. They accumulate as wastes in the processing of agricultural... 

Fractionation and Chemistry of Citrus Pectic Polysaccharides. Pectic polysaccharides, commonly known as pectin, appear early in plant cell-wall formation. A series of complex biochemical steps results in the formation of cell plates followed first by its growth in area (primary cell wall) then in thickness (secondary cell wa.ll). Exclusive of randomly oriented cellulose fibrils, primary cell wall is composed mainly of pectic polysaccharides (34). These pectic polysaccharides are rich in D-galacturonic acid, D-galactose and L-arabinose residues. With growth in thickness of cell wall (secondary cell wall),there appears to be a replacement of pectic polysaccharide deposition with polysaccharides rich in D-glucuronic acid or 4-0-methyl-D-glucuronic acid,... 

Polysaccharides Long chains of monosaccharides joined together are collectively called polysaccharides. The major storage polysaccharides are glycogen (in animals), starch (in plants) and dextran (in yeast and bacteria). Cellulose is a structural polysaccharide found in plant cell walls. 

Lignin is the third most abundant structural polymeric material found in plant cell walls typically comprising up to 20-30% of woody biomass, from which most lignin is sourced as a by-product of papermaking. Lignin binds hemicellulose and cellulose together in plant cell walls and shields them from enzymic and chemical degradation. 

Cellulose a highly abundant polysaccharide found in plant cell walls that is composed of long linear chains of glucose units connected as h -fi-glycoside linkages. 

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