Polysaccharides storage, synthesis

Glycolysis entails the breakdown of hexoses to 3 carbon compounds while producing ATP. The reverse process, gluconeogenesis entails the synthesis of hexose and related energy storage polysaccharides in a process that consumes ATP. 

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. 

Carbohydrates in algae and plants are often classified based on methodological discrimination. The structural carbohydrates are not water-soluble, whereas the other types of carbohydrates are water-soluble and typically extracted by hot water. In Phaeocystis five different pools of carbohydrates can be distinguished. Like all algal and plant cells, both solitary and colonial cells produce (1) structural carbohydrates, polysaccharides that are mainly part of the cell wall, (2) mono- and oligosaccharides, which are present as intermediates in the synthesis and catabolism of cell components, and (3) intracellular storage glucan. Colonial cells of Phaeocystis excrete (4) mucopolysaccharides, heteropolysaccharides that... 

It is now many years since it was discovered that heparin is a constituent of the mast cell granule. Because it has been found in mast cells, many assume that this cell is the principal site of synthesis of this polysaccharide. However, there is evidence also that fibroblasts not only make hyaluronic acid, but possibly sulfated chondroitin polysaccharides as well. - There is not always a distinct correlation between the numbers of mast cells and the content of heparin of a particular tissue. The mast cell is found only in connective and reticular tissues. There is some evidence that mast cells in culture may synthesize heparin.However, another point of view has been put forward that the fibroblasts may make the polysaccharide and store it for a time and that, when they are full of these storage granules, they are called mast cells. ... 

The ATP consumed in these reactions can be reconverted to ATP by numerous other reactions which occur in cells. Arginine phosphate (11.9b) appears to serve the same storage purpose in invertebrates. These compounds are sometimes called phosphagens. Adenosine triphosphate, ATP, is involved in the synthesis of all the essential biopolymers, that is, proteins, polysaccharides lipids... 

Each turn of the cycle may be summarized as the formation of 3 pentose molecules from 5 triose molecules. The carboxylation reaction forms 6 phosphoglycerates from the 3 pentoses. The net increase in compounds of this cycle may be balanced by the withdrawal of substances for the synthesis of cell constituents or, for the most part, by storage of hexose as polysaccharides (Chapter V). 

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