Carbon carbohydrate structure

Cellulose and starch are macromolecules with empirical formulas that resemble hydrated carbon, CX (H2 0)y, where x and y are integers. The monomers from which these macromolecules are consfructed are sugars such as glucose and fructose. These monomers and macromolecules are the carbohydrates. Structurally, carbohydrates are very different from simple combinations of carbon and water. Even the smallest carbohydrates contain carbon chains with hydrogen atoms, OH groups, and occasional ether linkages. 

A. Dondoni, M. Kleban, and A. Marra, The assembly of Carbon-linked calix-arene-carbohydrate structures (C-calixsugars) by multiple Wittig olefination, Tetrahedron Lett., 38 (1997) 7801-7804. 

The light reactions illustrated in Figure E9.1 are accompanied by a sequence of dark reactions leading to the formation of carbon intermediates and sugars. This sequence of reactions, called the Calvin cycle, incorporates C02 into carbohydrate structures. 

The carbohydrate most likely to appear on the MCAT is fructose or glucose. Both are six carbon carbohydrates called hexoses. These may appear as Fischer projections or ring structures. The Fischer projections are shown below ... 

When considering biomass as a source of chemical feedstock, it is also important to remember that it is not a homogeneous organic structure. The carbohydrate structures of terrestrial plants are composed of both five-carbon and six-carbon sugar polymers. The lignin component, which binds the polymers together, is an aromatic polymer of nominally propyl-methoxyphenols. In addition, there are proteins and fatty acids/oils, as well as the trace biocomponents that incorporate much of the mineral content. Therefore, processing biomass to chemical products must take into consideration both its bulk chemical structure and its components. 

In mammalian cells, glucose is the most abundant carbohydrate energy source. It is metabolized in all cells as a glycolytic fuel and is stored in liver and muscle as the polymer glycogen. But certain cells have the enzymes to catalyze the synthesis of glucose under certain conditions. The requirements are (1) the availability of specific carbon skeletons (carbon backbone structures of various types), (2) energy, in the form of ATP, necessary to accomplish the sequence of reactions, and (3) the enzymes to catalyze reactions of the sequence. 

As briefly discussed above, every synthesis that will be described involves the addition of one linking carbon between two cyclic carbohydrate structures in order to replace the anomeric oxygen. The easiest route to accomplishing this task is to target a (1 6) linkage because the... 

Like other compounds that contain two or more - OH or - O groups on adjacent carbon atoms, carbohydrates undergo oxidative cleavage by periodic acid, HIO4 (Sec. 16.12). This reaction, introduced in 1928 by L. Malaprade (at the University of Nancy, France), is one of the most useful tools in modern research on carbohydrate structure. 

Thinking Criticaiiy If a carbohydrate has 2" possible isomers, where n is equal to the number of carbon atoms in the carbohydrate structure that are... 

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. 

For the carbohydrate structures, the CRYSNET facility was used.4 The carbon and hydrogen atoms are shown as small, solid circles, and other atoms by the appropriate symbol. Where positions of hydrogen atoms were not reported, or could not be deduced, the atom is indicated by H. 

NMR techniques used in combination with databases is helpful for carbohydrate analysis. For example, SUGABASE is a carbohydrate-NMR database that combines CarbBank complex carbohydrate structure data (CCSD) with proton and carbon chemical shift values (151). 

Fischer Projection (or Fischer-Pollens projection) A planar projection formula in which the vertical bonds lie behind the plane of the paper and the horizontal bonds lie above the plane. Used commonly in carbohydrate structures, where each carbon in turn is placed in the proper orientation for planar projection. 

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