Cell wall of plant cells

Cell walls of plant cells. These are strong structures that provide stiffness and strength. Cell walls are composed mostly of cellulose, which will be discussed later in this chapter. 

Cellulose is a polymer found in the cell walls of plant cells such as those of wood, cotton, and leaves. It is responsible for giving plants their structural strength. Can you find the portions of the cellulose structure that repeat Notice that the ring parts of the molecule are all identical. These are the monomer units that combine to form the polymer. Glucose is the name of the monomer found in cellulose. In Figures 18.17 and... 

Protopectin is composed of water-insoluble pectic substances, which are fixed to the middle lamella and primary cell walls of plant cells. The neutral sugar side chain of the pectin is attached to the xyloglucan residues, which are bound to the cellulose fibers. The protopectin includes polyvalent such as calcium (Fig. 11.4-8). Protopectin is present in unripe fruits. During the maturation process of fruits or after harvesting, the protopectin is converted to soluble pectin11851. The insolubility of protopectin may be due to the polymerization of the molecule and to the cross-linking with divalent cations11861. 

Polysaccharide materials are the most abundant and diverse molecules present as an integral part of the natural system on this planet. They are renewable, biodegradable and can be cultivated as plant biomass, which is essentially made of polysaccharides. Nature has been using polysaccharides from time immemorial. Polysaccharides serve as structural material (e.g. the cell walls of plant cells), and are used for energy storage in the form of starch in plant cells and as glycogen in the liver cells of animals. 

Cellulose is found in the cell wall of plant cells and helps to give plants their structure. It is found in large amounts in trees and cotton fibres (which are nearly pure cellulose). Cellulose has many uses, including the making of paper. Cellulose molecules have many O-H bonds and the strength of wood is due, in part, to hydrogen bonding between nearby molecules. 

The major classes of organic compounds common to living systems are lipids pro terns nucleic acids and carbohydrates Carbohydrates are very familiar to us— we call many of them sugars They make up a substantial portion of the food we eat and provide most of the energy that keeps the human engine running Carbohy drates are structural components of the walls of plant cells and the wood of trees Genetic information is stored and transferred by way of nucleic acids specialized derivatives of carbohydrates which we 11 examine m more detail m Chapter 28... 

McNeil, M., Darvill, A. G., Fry, S. C., and Albersheim, P, 1984. Structure and fnncdon of die primary cell walls of plants. Annual Review of Biocheviistry 53 625-664. 

El Gueddari N.E. Rauchhaus U. Moerschbacher B.M. Deising H.B. (2002) Developmentally regulated conversion of surface-exposed chitin to chitosan in cell walls of plant pathogenic fimgi // New Phytologist. V. 156. P. 103-112. 

Biosorption is a rather complex process affected by several factors that include different binding mechanisms (Figure 10.4). Most of the functional groups responsible for metal binding are found in cell walls and include carboxyl, hydroxyl, sulfate, sulfhydryl, phosphate, amino, amide, imine, and imidazol moieties.4 90 The cell wall of plant biomass has proteins, lipids, carbohydrate polymers (cellulose, xylane, mannan, etc.), and inorganic ions of Ca(II), Mg(II), and so on. The carboxylic and phosphate groups in the cell wall are the main acidic functional groups that affect directly the adsorption capacity of the biomass.101... 

These protruding structures may form catalytic sites or binding sites for small molecules. Remarkably, some polysaccharide modification enzymes of pathogenic bacteria are similar to enzymes of their host cells. For example, during cell development, pectin, a principal component in the primary cell wall of plants, is modified by its own pectin methylesterases that have /1-solenoid structures (Johansson et al, 2002) and in this respect, resemble pectin lyases secreted by bacteria to break down these structures (Lietzke et al., 1996). 

Occurrence in plant Cell interior Structural tightly bound to cellulose wall of plant cell... 

The best-known aldopentose (1), D-ribose, is a component of RNA and of nucleotide coenzymes and is widely distributed. In these compounds, ribose always exists in the fura-nose form (see p. 34). Like ribose, D-xylose and L-arabinose are rarely found in free form. However, large amounts of both sugars are found as constituents of polysaccharides in the walls of plant cells (see p.42). 

Polysaccharides are composed of many monosaccharides bonded together. Common polysaccharides are cellulose, starch, and glycogen. Cellulose forms the structural material of the cell walls of plants. Cellulose is a polymer of glucose and consists of thousands of glucose molecules linked in an unbranched chain (Figure 16.6). 

Cellulose, a fibrous, tough, water-insoluble substance, is found in the cell walls of plants, particularly in stalks, stems, trunks, and all the woody portions of the plant body. Cellulose constitutes much of the mass of wood, and cotton is almost pure cellulose. Like amylose and the main chains of amylopectin and glycogen, the cellulose molecule is a linear, unbranched homopolysaccharide, consisting of 10,000 to 15,000 D-glucose units. But there is a very important difference in cellulose the glucose residues have the /3 configuration (Fig. 7-16),... 

The primary cell-wall of plants is formed by microfibrils of cellulose in a complex matrix of polysaccharides, proteins, and glycoproteins. The structure and relationship of the different components is under continuous study and revision, and most of them can now be identified and their biosynthesis studied.124"126... 

The fibrous tissue in the cell walls of plants contains the polysaccharide cellulose, which consists of long chains of glucose units, each of which is connected by a /3-glucoside link to the C4 hydroxyl of another glucose as in the... 

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... 

Phenolic acids, and especially ferulic acid, which is abundantly present in cereals, is found esterified to the polysaccharides present in primary and secondary cell walls of plants. Ferulic acid is the major phenolic acid occurring in the cell walls of monocotyledons and appears as cis and the more abundant trans isomers (reviewed in [Klepacka and Forna, 2006]). Ferulic acid is found in wheat, maize, rye, barley [Sun et al., 2001], oats, spinach, sugar beet, and water chesnuts [Clifford, 1999], generally esterified, and rarely as free form, such as in barley [Yu et al., 2001]. It is esterified in primary cell walls to arabinoxylans (Fig. 2.4) in the aleurone layer and pericarp [Clifford, 1999], as in spinach [Fry, 1982] or in wheat bran [Smith and Hartley, 1983], Ferulic acid can also be found esterified to other hydroxycinnamic acids such as in Mongolian medicinal plants where it is found as feruloylpodospermic acid, which is... 

Pectin is a polysaccharide found in the nonwoody cell walls of plants where it binds cells together and helps the plant take in water. In fruits, it is broken down during the ripening process, and this is why ripe fruits are soft. The fruits that contain the most pectin are apples, plums, grapefruits, and oranges. Pectin is commonly used as a food additive, especially as a thickener for jams and marmalades, where it provides the jellylike consistency. 

Such membranes do actually exist. Many animal membranes and the cell walls of plants serve as more or less perfect semi-permeable membranes. Many films of inorganic substance also can be prepared which are permeable to water but not to dissolved substances. 

So what effect do these differences in stereochemistry and extent of branching have on the uses of these polysaccharides Because of the extended nature of its chains, cellulose is the most common structural component of plants. Cellulose makes up the main component of the cell wall of plants. Wood is approximately 50% cellulose, while fiber-producing plants such as flax, jute, and hemp are 65% to 80%. The seed hairs of cotton are virtually pure cellulose. The long fibers from cottonseed (up to 5 cm long and 9 to 25 jxm in diameter [Franz 1986)) are spun into thread that is then woven into fabric for clothing. Short fibers, called linters, are used as the raw materials for chemical derivatives such as cellulose acetate (see Chapter 4). 

A linear jS-1,4 polymer of D-glucopyranose. Cellulose forms the cell walls of plants and is the major constituent of wood and cotton, (p. 1137)... 

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