Monosaccharides, chemical structure

Since many essential nutrients (e.g., monosaccharides, amino acids, and vitamins) are water-soluble, they have low oil/water partition coefficients, which would suggest poor absorption from the GIT. However, to ensure adequate uptake of these materials from food, the intestine has developed specialized absorption mechanisms that depend on membrane participation and require the compound to have a specific chemical structure. Since these processes are discussed in Chapter 4, we will not dwell on them here. This carrier transport mechanism is illustrated in Fig. 9C. Absorption by a specialized carrier mechanism (from the rat intestine) has been shown to exist for several agents used in cancer chemotherapy (5-fluorouracil and 5-bromouracil) [37,38], which may be considered false nutrients in that their chemical structures are very similar to essential nutrients for which the intestine has a specialized transport mechanism. It would be instructive to examine some studies concerned with riboflavin and ascorbic acid absorption in humans, as these illustrate how one may treat urine data to explore the mechanism of absorption. If a compound is... 

How does the chemical structure of the monosaccharide glucose differ from that of the monosaccharide fructose ... 

Dennis, R.D., Baumeister, S., Geyer, R., Peter-Katalinic, J., Hartmann, R., Egge, H., Geyer, E. and Wiegandt, H. (1992) Glycosphingolipids in cestodes - chemical structures of ceramide monosaccharide, disaccharide, trisaccharide and tetrasaccharide from metacestodes of the fox tapeworm, Taenia crassiceps (Cestoda Cyclophyllidea). European Journal of Biochemistry 207, 1 053-1 062. 

Chemical structure elucidation of the carbohydrate moiety of a glycoprotein is a difficult problem because there is often chain branching and because the individual carbohydrate chains are not always identical. Specific exoglycosidases which release monosaccharide units only from the terminal nonreducing end of the carbohydrate chain are most useful in structural analysis. Among the enzymes available for sequence analysis... 

Figure 2 Mammalian monosaccharides and nucleotide sugars. (A) Chemical structures, common names, and abbreviations of the 11 monosaccharides found in mammalian glycans as well as ManNAc, the precursor for sialic acids. (B) Examples of the three classes of nucleotide sugars are provided by UDP-GIcNAc (Glc, GIcA, Gal, GalNAc, and Xyl also use UDP), GDP-Man (Fuc also is linked to GDP), and CMP-Neu5Ac/Gc (IdoA is produced by postsynthetic epimerization of GIcA and therefore does not require a nucleotide sugar).

FIGURE 3.48 The chemical structure of monosaccharides currently applied in the solid phase synthesis. 

Starch and cellulose are polysaccharides. Sugar is easily solvable in water, where it forms hydrogen bonds with the water molecules. In Figure 11.4, the structures have been optimized by quantum chemical methods (PM3). Water molecules are added to all possible cavities to simulate the solvated structure. Hydrogen bonds are formed between the saccharide and the water molecules. If optimization is done in open space, on the other hand, hydrogen bonds are formed between and in the monosaccharides. This structure appears in a water-free crystal. In the aqueous solution simulated in Figure 11.4, the final strnctme is relevant for aqueous solution. 

The discovery of enzymes that could selectively break down hyaluronan opened the door for the establishment of the polysaccharide molecule s chemical structure. In those days, a powerful tool for analysing the structure of polysaccharides such as nuclear magnetic resonance spectroscopy NMR was not known. At the present time, NMR makes it possible to determine the monosaccharide biopolymer residue s composition, centres for substitution reactions, sequence and three-dimensional structure. 

A relationship between chemical structure and g.c. retention index has been developed for permethylated, peracetylated or pertrimethylsilylated alditols, so that a tentative identification of monosaccharides present at trace levels can be made. ... 

Anthocyanins are glycosides of glucose, galactose, rhamnose, arabinose or other monosaccharides of flavylinm cation derivatives. Up to now, more than 500 different anthocyanins were reported [Castaneda-Ovando et al., 2009]. Their stmctnre mainly differs by the number and the position of hydroxyl groups and the nature and number of bonded saccharides. The aglycons of anthoeyanins, the anthocyanidins, are however limited to a few chemical structures. So far, only 23 anthocyanidins were identified of which only 6 are... 

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