HOMOPOLYSACCHARIDES AND HETEROPOLYSACCHARIDES PDF

Homopolysaccharides contain only a single type of monomeric unit; heteropolysaccharides contain two or more different kinds of monomeric units ( Fig. ). Homopolysaccharides are polysaccharides composed of a single type of sugar monomer. For example, cellulose is an unbranched homopolysaccharide made. Carbohydrate – Heteropolysaccharides: In general, heteropolysaccharides ( heteroglycans) contain two The major heteropolysaccharides include the connective-tissue polysaccharides, the blood group substances, Homopolysaccharides.

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In general, heteropolysaccharides heteroglycans contain two or more different monosaccharide units. Although a few representatives contain three or more different monosaccharides, most naturally occurring heteroglycans contain only two different ones and are closely associated with lipid or protein.

The complex nature heteropolysaccharixes these substances has made detailed structural studies extremely difficult. The major heteropolysaccharides include the connective-tissue polysaccharides, the blood group substances, glycoproteins combinations of carbohydrates and proteins such as gamma globulinand glycolipids combinations of carbohydrates homopllysaccharides lipidsparticularly those found in the central nervous system of animals and in a wide variety of plant gums.

The most important heteropolysaccharides are found in the connective tissues of all animals and include a group of large molecules that vary in size, shape, and interaction with other body substances.

They have a structural role, and the structures of individual connective-tissue polysaccharides are related to specific hoompolysaccharides functions; hyaluronic acid, for example, the major component of joint hetsropolysaccharides in animals, functions as a lubricating agent and shock absorber.

The connective-tissue heteropolysaccharides contain acidic groups uronic acids or sulfate groups and can bind both water and inorganic metal ions. They can also play a heteropolysaccharudes in other physiological functions; e. Ion-binding ability also appears to be related to the anticoagulant activity of the heteropolysaccharide heparin. The size of the carbohydrate portion of glycoproteins such as gamma globulin or hen-egg albumin is usually between five and 10 monosaccharide units; several such units occur in some glycoprotein molecules.

The function of the carbohydrate component has not yet been established except for glycoproteins heteropolysacchariddes with cell surfaces; in this case, they appear to act as antigenic determinants—i. In general, monosaccharides are prepared by breakdown with acids of the polysaccharides in which they occur.

The techniques employed for separation of monosaccharides depend to some extent on their physical and chemical properties; chromatographic procedures are often used.

Oligosaccharides and polysaccharides are prepared from natural sources by techniques that take advantage of size, alkaline stability, or some combination of these and other properties of the molecule of interest. It should be noted that preparation of an oligosaccharide or polysaccharide usually results in a range of molecular sizes of the desired molecule.

The purity of a homopolyaaccharides preparation, which is frequently based on an analysis of its compositionis more easily established for monosaccharides and disaccharides than for heteropolsaccharides, insoluble molecules such as cellulose.

A variety of organic chemical analytical techniques are generally applicable to studies involving carbohydrates. Optical rotation, for example, once was frequently used to characterize carbohydrates. Optical rotation is no longer widely used homopoltsaccharides characterize monosaccharides.

Optical rotation is not a completely additive property; a trisaccharide composed of three glucose residues, for example, does not have a rotation three times that of one glucose molecule. Sugar alcohols cannot form ring structures; their rotation values are extremely small, suggesting a relationship between ring structure and the ability of a carbohydrate to rotate the plane of polarized light. Certain types of reactions e.

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This technique is frequently used to examine the breakdown of disaccharides or oligosaccharides to monosaccharide units, especially if a large change in the net optical rotation may be expected, as occurs in the hydrolysis of sucrose.

Several other optical techniques used in chemistry have been applied to the analysis of carbohydrates. Infrared spectroscopyused to measure vibrational and rotational excitation of molecules, and nuclear magnetic-resonance spectroscopywhich measures the excitation of certain components of molecules in a magnetic field induced by radio-frequency radiation, are valuable, although the similarity of the functional groups i.

Proton magnetic-resonance spectroscopy, nuclear magnetic resonance applied to protons H atomsis employed to identify the relative spatial arrangements of individual hydrogen atoms in a molecule.

When they are precisely placed, the corresponding positions of the hydroxyl groups attached to the same carbon atom can be deduced. An extension of this technique utilizes the resonance spectroscopy of carbon, a nonradioactive isotope of carbon, so that ring structures can be established with great accuracy.

Both the proton and carbon magnetic resonance methods are best applied to monosaccharides; they are less valuable in studying hfteropolysaccharides because an individual hydrogen atom in a heteropolyssaccharides molecule is too small for accurate detection. The study of polysaccharide structure usually focuses on the homopolyysaccharides composition, the linkage between the monosaccharide units, and the size and shape of the molecule.

The size and shape of a polysaccharide can be ascertained by techniques that are usually applied to large molecules; e. Indications of the shape of polysaccharide molecules in solution are obtained from viscosity measurements, in which the resistance of the molecules to flow viscosity is equated with the end-to-end length of the molecule; the viscosity of hyaluronic acid, for example, shows a marked dependence on both concentration of the acid and homopoysaccharides salt content of the solution, and, under conditions approximating those found in biological systems, a hyaluronic acid molecule may be thought of as occupying a great deal of space.

Alternatively, the compact nature of a glycogen molecule of molecular weight equal to that of a molecule of hyaluronic acid results in its accommodation to a much smaller space than the latter molecule.

The identification of sugars in a mixture resulting from the hydrolytic breakdown of a heteropolysaccharide is most often carried out by chromatography of the mixture on paper, silica gelor cellulose. Ready separations can be achieved between pentoses, hexoses and, for example, deoxy sugars; closely related compounds such as d -glucose and d -galactose also can be separated using chromatographic techniques.

The linkage positions in polysaccharides are usually determined using the methylation procedure described previously. The various monosaccharide methyl ethers produced by the methylation are separated by gas—liquid chromatography. Detailed statements about polysaccharide structure and function are limited by the statistical nature of some measurements e. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind.

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Heteropolysaccharides In general, heteropolysaccharides heteroglycans contain two or more different monosaccharide units. Page 8 of 8.

Homopolysaccharide

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Structural Biochemistry/Carbohydrates/Polysaccharides

Introduction General features Classification and nomenclature Biological significance Role in the biosphere Role in human nutrition Role in energy storage Role in plant and animal structure Structural arrangements and properties Stereoisomerism Configuration Hemiacetal and hemiketal forms Classes of carbohydrates Monosaccharides Sources Chemical reactions Formation of glycosides Formation of methyl ethers Disaccharides and oligosaccharides Sucrose and trehalose Lactose and maltose Polysaccharides Homopolysaccharides Heteropolysaccharides Preparation and analysis Analytical techniques Spectroscopic techniques Identification of subunits.

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Exopolysaccharides Production by Lactic Acid Bacteria

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