Polysaccharide biopolymers branching

Many polysaccharides contain branched structures and are chemically modified by the addition of other molecules. Their monomeric or repeat units are often made up of more than one sugar molecule and, consequently, can be quite complex. They form protective capsules of some of the most virulent microorganisms, capsules that, nevertheless, carry information that activate mammalian defenses the immune, interferon, and properdin systems [9, 136]. They are found as key portions of the exoskeletons of insects and arthropods and cell walls of plants and microbes and perform as reserve foodstuffs and important components of intercellular, mucous secretions, synovial and ocular fluids, and blood serum in many organisms. Food Applications compiles recent data on the food applications of marine polysaccharides from such various sources as fishery products, microorganisms, seaweeds, microalgae, and corals [137, 138]. One of the applications of this biopolymer relates to a method for protecting against diseases induced by Streptococcus pneumoniae infections, which comprises mucosal administration of a S. pneumoniae capsular polysaccharide to a patient in need. 

The chemistry of polysaccharides is a major frontier. Their branched and complex nature makes them far more difficult to synthesize than the linear biopolymers, proteins, and nucleic acids. For this reason, automated synthetic methods for polysaccharides were just created in 2001, several decades after com-... 

The phase separation threshold is lower for systems containing a branched polysaccharide than for systems containing a linear polysaccharide of the same molecular weight. It is higher for globular proteins compared to proteins of unfolded structure. An increase in excluded volume means a decrease in the free volume of the solution accessible for biopolymers. Thus, the excluded volume of biopolymer molecules implies that water in real foods can be nonsolvent water relative to macromolecules. 

The binodal branches do not coincide with the phase diagram axes. This means that the biopolymers are limitedly cosoluble. For instance, on mixing a protein solution A and a polysaccharide solution B a mixture of composition C can be obtained. This mixed solution spontaneously breaks down into two liquid phases, phase D and phase E. Phase D is rich in protein and E is rich in polysaccharide. These two liquid phases form a water-in-water (WIW) emulsion. Hie phase volume ratio is estimated by the inverse lever rule. The phase D/phase E volume ratio equals the ratio of the tieline segments EC/CD. Point F represents the phase separation threshold, that is, the minimal critical concentration of biopolymers required for phase separation to occur. 

Between 1950 and 1960 Size Exclusion Chromatography (SEC) became a popular technique in two branches the fractionation of synthetic polymers, described as gel permeation chromatography, and in the resolution of biopolymers, termed as gelfil-tration. The former was performed on cross-linked porous synthetic polymers, the latter on cross-linked polysaccharides (Sephadex). 

Starch is a naturally occurring biopolymer in which glucose is polymerized into amylose, an essentially linear polysaccharide, and amylopectin, a highly branched polysaccharide. Starch occurs in plant tissues in the form of discreet granules whose size, shape, and form are unique to each botanical species (Woolfe, 1992). Sweet potato roots contain approximately 80-90%... 

Primary structure (1° structure) is the arrangement (or sequence) of monomeric residues in the covalently linked biopolymers. This arrangement is linear for nucleic acids and proteins, but can be branched in polysaccharides. 

Polymers are mainly classified into two categories, natural and synthetic polymers (Table 30.1). Natural (water soluble) polymers are mostly obtained from natural sources. Naturally derived polymers with special focus on polysaccharides and proteins have become attractive in the biological applications of controlled release systems. Polysaccharides are a class of biopolymers constituted by either one or two alternating monosaccharides, which differ in their monosaccharide units in the length of a chain, in the types of the linking units, and in the degree of branching. ... 

Self-assembled nanostructures of biopolymers play an important role in nature. For example, extracellular branched polysaccharides decorate bacterial surfaces and therewith mediate cell adhesion [11], aggrecans (protein-polysaccharide complexes) control mechanical stresses in synovial joints [12], whereas neurofilaments (neuron-specific protein assemblies) support the elongated cell shape and participate in the maintenance of the axonal caliber [13]. It is believed that these biological functions rest on the ability of bioassemblies to provide adequate responses to variations in the local environment. Therefore, a better understanding of the physical mechanisms that govern conformational rearrangements in (bio)nanostructures, is of key importance, not only for colloid and material sciences, but also for cell biology. 

The multiplicity of possible branching points along polysaccharide chains will allow build up into arrangements more complex than those possible with other biopolymers such as proteins (Section 10.2) and nucleic acids (Section 10.4). These possible variations of polysaccharide structure arise in addition to the types of isomerism associated with individual monosaccharide units discussed above. 

Gelling Polysaccharides Gelling polysaccharides are generally more complex than structural polysaccharides in (1). They are hetero polysaccharides built from mixed monomer units and they contain many branched in addition to the straight chains as depicted in Equation 10.20e for starch. Starch, the second most abundant biopolymer, is probably the most important (below). 

Starch is a natural polymer available in large quantities from various sources. It can be obtained from different plants for which it is the most common source of polysaccharides of energetic reserve. In its native state, starch consists of semicrystalline granules insoluble in water. It is composed of two polysaccharides, branched amylopectin and essentially linear amylose. Starch is cheap, environmentally friendly and a completely biodegradable biopolymer, which has been also used to reinforce NR composites as filler. 

Other large scale biopolymers are polysaccharides. Polysaccharides are relatively complex carbohydrates. They are polymers made up of many monosaccharides joined together by glycosidic linkages. They are therefore very large, often branched, macromolecules. Polysaccharides tend to be amorphous, insoluble in water, and have no sweet taste. When all the constituent monosaccharides are of the same type they are termed homopoly saccharides, when more than one type of monosaccharide is present they are termed heteropolysaccharides. Examples include storage polysaccharides such as starch and glycogen and structural polysaccharides such as cellulose and chitin. 

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