Glucose photosynthetic production

These reactions of course occur in the presence of the proper enzyme catalysts and coEactors. Glucose is the primary photosynthetic product. As will be shown later in the discussion of the structures of the organic intermediates in the various pathways, the dark reactions take place in such a manner that ribulose-1,5-diphosphate is regenerated. 

Polymers of fructose are of widespread occurrence in plants, but are common only in a few orders, particularly the Compositae ind Graminae, They differ in several respects from prokaryotic fructans, especially in that they are intracellular rather than extracellular, that they are far smaller than their bacterial counterparts and that they contain relatively more glucose. Their function in plants is as storage polysaccharides and they are synthesised, ultimately from photosynthetic products. In bacteria such polymers are often assembled from exogenous, rather than endogenous disaccharides. 

The quantity of carbon used annually in the photosynthetic production of glucose is enormous, being estimated at some 150 x 10 tons, requiring about 5 x 10 calories of solar energy. This conversion is achieved largely in forests, which are consequently responsible for controlling the level of oxygen and carbon dioxide in the atmosphere. 

Benson and Calvin showed that when algae were allowed to photo-synthesize for short periods in the presence of C Mabeled sodium bicarbonate and the photosynthetic products were separated on a paper chromatogram, the first free carbohydrate that appeared after short photosynthetic periods of 30 to 90 seconds was sucrose. Glucose and fructose were also present but they were not radioactive. These authors have reasoned that if free glucose or free fructose were intermediates in the synthesis of sucrose, they should have become radioactive either prior to the appearance of radioactive sucrose or simultaneously with it. They therefore suggested that the immediate sucrose precursors are probably glucose-l-phosphate and fructose-6-phosphate and that the disaocharide... 

Although the reactions of gluconeogenesis are the same in all organisms, the metabolic context and the regulation of the pathway differ from one species to another and from tissue to tissue. In this section we focus on gluconeogenesis as it occurs in the mammalian liver. In Chapter 20 we show how photosynthetic organisms use this pathway to convert the primary products of photosynthesis into glucose, to be stored as sucrose or starch. 

The photosynthetic block precedes sucrose synthesis, and sucrose partially reverses the inhibition caused by the lack of fixation of carbon dioxide. D-Fructose disappears first, after treatment, followed by sucrose, and then u-glucose.188 It is likely that other metabolic systems are involved as well, since the amino acid distributions were not identical to the I4C02 dark-fixation products.189 Uptake of sucrose-14C increased some acids (as-... 

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