Carbohydrates, photosyntheses

A substance which proved to be a polymer of crotonic acid, also possessing the formula (C4HeO])n that has just been mentioned, has been extracted from certain purple bacteria. It is formed during the metabolism of some photosynthesizing bacilli and occurs as a reduction product of compounds of carbohydrate nature. 

As distinct from the purple bacteria, plants, when photosynthesizing carbohydrates from C02, use water rather than H2S as an oxidized substrate. The oxidation of water requires far more energy than that of hydrogen sulphide. This circumstance plus the necessity for the sites of formation of oxidized and reduced particles to be spatially separated (in order to avoid their rapid recombination) seems to be the reason for the formation in plants... 

Other than a brief collaboration with S. AronofF, A. Benson, and M. Calvin (1947) on the distribution of label in photosynthesizing plant-tissue, this short sojourn by Hassid in the field of photosynthesis was not continued, and his involvement appears to have been based more on an interest in carbohydrate structural analysis than in the fundamentals of carbon fixation in plants. However, it is apparent from the later turn of events that this introduction to the utility of radioactive-tracer techniques for the elucidation of biochemical processes had a strong influence on his development. 

The incorporation of COz into carbohydrate by eukaryotic photosynthesizing organisms, a process that occurs within chloroplast stroma, is often referred to as the Calvin cycle. Because the reactions of the Calvin cycle can occur without light if sufficient ATP and NADPH are supplied, they have often been called the dark reactions. The name dark reactions is somewhat misleading, however. The Calvin cycle reactions typically occur only when the plant is illuminated, because ATP and NADPH are produced by the light reactions. Therefore light-independent reactions is a more appropriate term. Because of the types of reactions that occur in the Calvin cycle, it is also referred to as the reductive pentose phosphate cycle (RPP cycle) and the photo synthetic carbon reduction cycle (PCR cycle). 

The first autotrophes to use the Sun s energy (i.e. photosynthesizers) would also have been prokaryotic anaerobes hving in aquatic environments, and they used hydrogen sulphide as a source of the hydrogen needed for carbohydrate synthesis, yielding sulphur as a byproduct, not oxygen ... 

Effect of Externally Supplied 1% C Carbohydrates ON THE Release of Fixed from Xanthoria aureola (Photosynthesizing) on Illuminated NaH Coa Solutions"... 

This experiment needs to be repeated with the modification that the lichens are first allowed to photosynthesize for a period of a few hours on distilled water without added This would allow the various carbohydrate... 

Today it is estimated that 3.4 X 10 " kg (4 X 10 tons) of carbohydrate are biosynthesized each year on the Earth by plants and photosynthesizing bacteria. Carbohydrates make up an important constituent in the human diet and provide a high proportion (50-60%) of the calories consumed. Carbohydrates are also utilized as structural materials in plants, animals, and microorganisms. 

The reactions involved in the fixing of CO2 and its incorporation into carbohydrates by photosynthesizing organisms are complicated. These reactions were studied by Melvin Calvin and his associates James Bassham and Andrew Benson over a ten-year period from 1946 to 1956. They used " C-labeled CO2 and traced the metabolic fate of the CO2 by exposing it to growing cultures of algae Chlorella) for various periods of time. They analyzed what radioactive com-... 

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