Structures and Functions of Polysaccharides

When many monosaccharides are linked together, the result is a polysaccharide. Polysaccharides that occur in organisms are usually composed of a very few types of monosaccharide components. A polymer that consists of only one type of monosaccharide is a homopolysaccharide a polymer that consists of more than one type of monosaccharide is a heteropolysaccharide. Glucose is the most common monomer. When there is more than one type of monomer, frequently only two types of molecules occur in a repeating sequence. A complete characterization of a polysaccharide includes specification of which monomers are present and, if necessary, the sequence of monomers. It also requires that the type 

I FIGURE 10.21 The polymeric structure of cellulose. P-Cellobiose is the repeating 

The importance of carbohydrates as energy sources suggests that there is some use for polysaccharides in metabolism. We shall now discuss in more detail some polysaccharides, such as starches, that serve as vehicles for storage of glucose. 

Second, when an organism needs enei quickly, the glycogen phosphorylase has more potential targets if there are more branches, allowing a quicker mobilization of glucose. Again, this is not as important to a plant, so there was no evolutionary pressure to make starch highly branched. 

What role do polysaccharides play in the structure of cell walls  

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M.B. Nieto, Structure and function of polysaccharide gum-based edible films and coatings, in K.G. Huber, and M.E. Embuscado, eds.. Edible Films and Coatings for Food Applications, Springer New York, pp. 57-112,2009. 

The polysaccharide synthesis via ring-opening polymerization method is an attractive method leading to structurally well-defined polysaccharides which are rarely attained by direct chemical modifications of natural polysaccharides. The synthetic polysaccharides obtained are useful tools to elucidate relations between the structure and functionality of polysaccharides and to develop new types of polysaccharides with novel properties. 

In most cases, the precise functions of polysaccharides are not known even their primary sequences are very hard to determine using current analytical techniques. Thus, a major challenge is to crack the carbohydrate code and determine the structures and functions of all the polysaccharides found on human cells. Terms such as glycomics have already been coined to describe such global efforts. 

O Neill, M. A., Ishii, T., Albersheim, P, Darvill, A. G. (2004). Rhamnogalacturonan II structure and function of a borate cross-linked cell wall pectic polysaccharide. Ann. Rev. Plant Biol, 55,109-139. 

The chapters of Part I are devoted to the structure and function of the major classes of cellular constituents water (Chapter 2), amino acids and proteins (Chapters 3 through 6), sugars and polysaccharides (Chapter 7), nucleotides and nucleic acids (Chapter 8), fatty acids and lipids (Chapter 10), and, finally, membranes and membrane signaling proteins (Chapters 11 and 12). We supplement this discourse on molecules with information about the technologies used to study them. Some of the techniques sections are woven throughout the molecular descriptions, although one entire chapter (Chapter 9) is devoted to an integrated... 

BeMiller JN (2001) Classification, structure, and chemistry of polysaccharides in foods. In Cho SS, Dreher M (eds) Handbook of dietary fiber and functional foods. Marcel Dekker, New York, chap 31... 

In the following section, enzymes in the EC 2.4 class are presented that catalyze the polymerization of polysaccharides. The Enzyme Commission classification scheme organizes enzymes according to their biochemical function in living systems. Enzymes can, however, also catalyze the reverse reaction which is very often used in biocatalytic synthesis. Therefore newer classification systems have been developed, based on the three-dimensional structure and function of the enzyme, the property of the enzyme, the biotransformation that the enzyme catalyzes etc. [10-15]. The Carbohydrate-Active enZYmes Database [13], which is currently the best database/classification system for carbohydrate active enzymes, uses an amino acid sequence-based classification and would classify some of the enzymes presented in the following as hydrolases rather than transferases (e.g., branching enzyme, sucrases and amylomaltase). Nevertheless we present these enzymes here because they are transferases according to the EC classification. 

The extracellular matrix (ECM) is a complex meshwork of proteins and polysaccharides that contributes to the structure and function of a tissue. 

Darvill AG, Albersheim P, McNeil M, et al. 1985 Structure and function of plant cell wall polysaccharides. J Cell Sci, Supple 2 203-217. 

Ishii, T. Structure and functions of feruloylated polysaccharides. Plant Sci, 127, 111, 1997. 

Analytical Techniques to Evaluate the Structure and Function of Natural Polysaccharides, Glycosaminoglycans, ed. N. Volpi, Research Signpost Trivandrum, India, 2002... 

It can be said that chitin is most relevant to our health and welfare, because of the very important interactions between human life and chitin-based life 1. To explain the importance of the knowledge of the chemistry of chitin for the biomedical sciences, we could mention the well-known investigation on structure and function of lysozyme carried out with chitin oligomers lysozyme is present in human body fluids as a defence against chitinous organisms on which it exerts hydrolytic action. A further example is the research on heparin and heparinoids heparin is probably the polysaccharide most closely related to chitin that can be found in the human body, where it reacts specifically with blood components to control blood fluidity and coagulation. 

As several novel reactions satisfying the criteria of click chemistry have been exposed in the last decade, we also mention the introduction of these new click reactions to the ground of polysaccharide chemistry, encompassing two metal-free [3 + 2] cycloaddition reactions, and the inverse electron-demand Diels-Alder reaction, In this section we emphasized on the chemistry of the reactions, and try to offer to readers a guide for executing such reactions. Simultaneously, the extremely diverse and controllable structures and functionalities of the click reaction products are established. Various types of chck reactions involved are illustrated in Fig. 4.4. In addition several examples of alkynes and azides generally used to functionalized polysaccharides are mentioned in Table 4.3. 

Naturally-occurring polysaccharides exhibit a variety of distinct physicochemical, physiological, and pharmaceutical properties. These properties and functions of polysaccharides depend on their chemical structures, which differ slightly in the kinds of monosaccharide components and functional groups, their positions, modes of linkage, and so on. The primary structures influence polysaccharide conformations, which determine highly-ordered solid structures and solution properties. 

Multipoint hydrogen-bonding is a nature s device for the maintenance of structures and functions of informational biopolymers such as nucleic acids, proteins, and oligo- and polysaccharides. Molecular recognition based on such interactions is still in an early stage, but there have eady been accumulated many good examples that convince one of its potential utilities in modem chemical science. 

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