Polysaccharides plant, metabolism

Studies performed over the years have contributed to better understanding of the interactions between proteins and tannins, which are important not only due to their astringency but also because of their impact on food nutritional characteristics, on human health, and on plant metabolism. It is clear that protein-tannin interactions are influenced by several factors, among which polysaccharides could be important because they are also present in tannin-rich vegetables. Much remains to be studied in this field, particularly the specific phenomenon that occurs between proteins, tannins, and polysaccharides that leads to a decrease in aggregation, and further studies are needed involving other salivary proteins and digestive enzymes. 

Carbohydrates are aldehydes or ketones of higher polyhydric alcohols or components that yield these derivatives on hydrolysis. They occur naturally in plants (where they are produced photosynthetically), animals and microorganisms and fulfil various structural and metabolic roles. Monosaccharides are the simplest carbohydrates and they often occur naturally as one of their chemical derivatives, usually as components of disaccharides or polysaccharides. 

In terms of function, polysaccharides fall into one of two groups structural and nutritional. For example, cellulose is a principal structural component of plants. Glycogen and starch, in contrast, are nutritional reservoirs for animals and plants, respectively. Monosaccharides may be mobilized from storage reservoirs such as glycogen and starch and then be metabolized to generate energy. 

Incubation of D-[U-I4C]apiose with sterile Lemma minor (duckweed) produced less than 0.01% incorporation into the cell-wall polysaccharides.75 Most of the d-[U-i4C]apiose appeared as 14C02 some remained in solution in the medium and in the duckweed plants, primarily as degradation products of D-[U-14C]apiose, but not as the branched-chain sugar.75 There is an efficient synthesis of the [U-14C]apiose moiety of cell-wall polysaccharides from D-[U-14C]glucose under similar conditions.81 Of the plant tissues tested, only L. minor contained an enzyme system able to metabolize free apiose. Carrot, lettuce, and spinach tissues are unable to metabolize the free, branched-chain sugar.75... 

There is thus some evidence for the tight binding of enzymes, especially glycosidases, to cell walls in both dicots and monocots. The nature and localization of these enzymes suggest that they may, perhaps, play a role in wall breakdown and such other processes as elongation growth. The membrane systems of plant cells are known to be involved in the transport, and introduction, of polysaccharides into the cell wall247-249 enzymes localized in the wall may also play a part in the metabolism of these polymers when they are transferred from the membrane system to the wall. 

The processes generating plant compounds have been separated into primary and secondary metabolism. Primary metabolism produces the basic products for the life of the plant like carbohydrates, amino acids, fatty acids, polysaccharides, proteins, lipids, RNA and DNA. The primary metabolites are produced in relatively large quantities and their distribution is universal. On the contrary, the secondary metabolites are... 

Because of its roles in the synthesis of glycogen, in isomerization of hexose phosphates, and as a precursor for numerous biosynthetic intermediates, UDP-glucose is regarded as a central hexose derivative in mammalian metabolism. In bacteria and plants, both ADP-glucose (production of storage polysaccharide) and UDP-glucose (sugar interconversions and biosynthesis) play important roles as precursors. 

The details of the metabolism of plant polysaccharides that contain a-D-galactopyranosyl residues are limited to D-galactomannans.12 However, published data on the exact mechanism of biosynthesis are still not available. 

Of the three naturally occurring hexuronic acids, D-glucuronic acid appears to be by far the most widely distributed. It has not been found free in Nature, except possibly in small amounts in blood and urine, but it occurs in a wide variety of polysaccharides and mucoproteins of plant, animal and bacterial origin, and plays an important part in the metabolism of many types of organic compounds. 

CARBOHYDRATES ARE IMPORTANT, naturally occurring organic compounds. They include simple sugars, or monosaccharides, such as glucose and fructose, and polysaccharides, such as starch and cellulose, which are more complex compounds composed of a number of sugar units. Carbohydrates are one of the initial products of photosynthesis. As such, they serve as the molecules that store the sun s energy for later use in metabolism. In addition, carbohydrate polymers are structural materials used by plants and animals. Even our genetic material, DNA, contains carbohydrate units as part of its polymeric backbone. 

Biological Functions of Oligosaccharides and Polysaccharides. Polysaccharides serve two important biological roles. Glycogen and starch are polymers of glucose units linked in a(l —> 4) linkages that serve as carbohydrate reserves for animals, bacteria, and plants. Because these polymers are readily converted to intermediates for pathways that yield metabolic energy, they can also be... 

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