Plant cell walls, molecular organization

Cellulose is the most abundant organic material found in nature (13). It is the primary component of plant cell walls and is therefore a large constituent of fruits and vegetables. Since cellulose is safe for human consumption, it is commonly used as an additive in food products. Cellulose and chemical derivatives of cellulose are also widely used as excipients in pharmaceutical applications. The biocompatibility of cellulose coupled with a molecular structure that is conducive to chemical modification, has made cellulose a staple of pharmaceutical formulations. Each anhydroglucose unit of the cellulose backbone contains three hydroxyl groups that provide reactive sites for chemical substitution. Thereby, cellulose can be chemically modified in a variety of ways to yield materials with differing properties useful for diverse pharmaceutical applications. 

Many questions about the molecular organization in plant cell walls... 

A classic example of the creation of macrostructure from molecular organization is cellulose-based fibre materials. Cellulose is the dominant polysaccharide in plant cell walls and is often touted as being the most abundant biopolymer on earth. A basic cellulose unit, known as the elementary fibril, contains thirty-six l,4-(3-D-linked polyanhydroglucopyranose chains (Figure 12.3a), and may eventually be coated with non-cellulosic polysaccharides to form the cell wall microfibril. These microfibrils are then crosslinked by hemicelluloses/pectin matrixes during cell growth. The cellulose molecule is constrained to adopt... 

The molecular mass of cellulose preparatious varies from about 50,000 to more than one million. Cellulose is organized into structures, microfibrils, which contain many molecules parallel to each other. These are localized in the cell walls of higher plants, providing strength. It is the strength of these cell walls that basically creates the structural stability of plants witness the strength of trees. 

Copper is an essential element. Copper plays a significant role in several physiological processes - photosynthesis, respiration, carbohydrate distribution, nitrogen reduction and fixation, protein metabolism, and cell wall metabolism. Many plant metalloenzymes contain copper. It also influences water permeability of xylem vessels and thus controls water relationships. It is mainly complexed with organic compounds of low molecular weight and with proteins (Henze and Umland, 1987). Kabata-Pendias and Pendias (1984) have compiled data on the Cu concentrations in... 

Cellulose is the most abundant organic substance found in nature. It is a linear polymer of glucose, with 500 - 5000 glucose units linked together to give molecules of molecular weight 100,000 to 1,000,000. It is the principal constituent of cell walls in higher plants. It occurs in almost pure form (98%) in cotton fibres and to a lessor extent in flax (80%), jute (60-70%), wood (40-50%) and cereal straws (30-43%). 

THE MAJOR CLASSES of organic compounds common to living systems are lipids, proteins, 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. Carbohydrates are structural components of the walls of plant cells and the wood of trees they are also major components of the exoskeletons of insects, crabs, and lobsters. Carbohydrates are found on every cell surface, where they provide the molecular basis for cell-to-cell communication. Genetic information is stored and transferred by way of nucleic acids, specialized derivatives of carbohydrates, which weTl examine in more detail in Chapter 26. 

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