Polysaccharide linearly branched type

Fig. 4.16. Schematic representation of the effective volumes of linear, branched and linearly branched types of polysaccharides...

Structural polysaccharides are almost always linear molecules, while polysaccharides that serve primarily as energy sources are commonly branched, or in some cases (e.g. starch) a mixture of linear and branched polysaccharides with the branched type predominating. In general, branched polysaccharides are easily soluble in water and have... 

Molecular Structure. Most starches consist of a mixture of two polysaccharide types amylose, an essentially linear polymer, and amylopectin, a highly branched polymer. The relative amounts of these starch fractions in a particular starch are a major factor in determining the properties of that starch. 

The integral intensities of signals of polysaccharides, obtained with a modem spectrometer under the usual operating conditions, are proportional or quasi-proportional, to the number of 13C nuclei present. This has been observed, in particular, in the case of linear hexo-pyranan structures containing one type,11,47,51,55,56 58-61 or two equal types, of linkage,62 or branched-chain polymers having two linkage types,53,58 where the resonances are readily resolved. In such cases, the T values would be low, 0.2 s or less, and the n.O.e. values would be approximately equal. However, few actual determinations of these values have been made, and extrapolation of such assumptions to more-complex polysaccharide structures is not recommended, as outlined in Section V,2,... 

Figure 14.2 Representative oligosaccharide structures found on mammalian glycoproteins and glycolipids. The complex oligosaccharides may be bi-, tri-, or tetra-antennary the branches may be more or less elongated with 1—>4 linked lactosamine units, and they may or may not be sialylated. The SLex, Lea, and Leb structures represent the different blood group determinants often present on lipids, and the elongated core 2 structure is a mucin-type glycosylation. Proteoglycans have a common core to which a variety of linear acidic polysaccharides are attached.

The bulk of all carbohydrates in nature exists in the form of polysaccharides. These are very large molecules formed by linking together long chains of monosaccharide units. These chains may be linear, like polypeptides or polynucleotides, or branched. They may contain a single type of monosaccharide unit, similar to polyglycine or polyA for example, or two or more types of monosaccharide, like nucleic acids (four types of nucleotides) or proteins (20 types of amino acids). However, polysaccharides that contain more than two types of monosaccharide are rare in nature. 

Polysaccharides that are formed from only one type of monosaccharide are called homo-glycans, while those formed from different sugar constituents are called heteroglycans. Both forms can exist as either linear or branched chains. 

Most potato starches are composed of a mixture of two polysaccharides, a linear fraction, amylose, and a highly branched fraction, amylopectin. The content of amylose is between 15 and 25% for most starches. The ratio of amylose to amylopectin varies from one starch to another. The two polysaccharides are homoglucans with only two types of chain linkage, a-(l 4) in the main chain and a-(l 6)-linked branch chains. Physicochemical properties of potato and its starch are believed to be influenced by amylose and amylopectin content, molecular weight, and molecular weight distribution, chain length and its distribution, and phosphorus content (Jane and Chen, 1992). 

Abbreviations for biosynthetic types are composed from abbreviations of nucleoside residues of activated forms of the monosaccharide components. 6 See footnote a to Table VI lin. and br. mean linear and branched polysaccharides. c Including other bacterial amphi-philes of Gram-negative, outer membranes. d Including amphiphiles of Gram-positive cell-membranes. 

The starch granule contains two polysaccharide types amylose, which is a linear polymer, and amylopectin, which is a branched polymer. Amylose is composed of linear chains of about 800 to 22,000 a-D-glucopyranosyl units in (a-1,4) linkage... 

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