Ho

Dextran

FIGURE 7-19 Conformation at the glycosidic bonds of cellulose, amylose, and dextran. The polymers are depicted as rigid pyranose rings joined by glycosidic bonds, with free rotation about these bonds. Note that in dextran there is also free rotation about the bond between C-5 and C-6 (torsion angle a> (omega)).

FIGURE 7-20 A map of favored conformations for oligosaccharides and polysaccharides. The torsion angles $ and $ (see Fig. 7-19), which define the spatial relationship between adjacent rings, can in principle have any value from 0° to 360°. In fact, some of the torsion angles would give conformations that are sterically hindered, whereas others give conformations that maximize hydrogen bonding. When the relative energy is plotted for each value of $ and $, with isoen-

ergy ("same energy") contours drawn at intervals of 1 kcal/mol above the minimum energy state, the result is a map of preferred conformations. This is analogous to the Ramachandran plot for peptides (see Figs 4-3, 4-9). The known conformations of the three polysaccharides shown in Figure 7-19 have been determined by x-ray crystallography, and all fall within the lowest-energy regions of the map.

FIGURE 7-20 A map of favored conformations for oligosaccharides and polysaccharides. The torsion angles $ and $ (see Fig. 7-19), which define the spatial relationship between adjacent rings, can in principle have any value from 0° to 360°. In fact, some of the torsion angles would give conformations that are sterically hindered, whereas others give conformations that maximize hydrogen bonding. When the relative energy is plotted for each value of $ and $, with isoen-

ergy ("same energy") contours drawn at intervals of 1 kcal/mol above the minimum energy state, the result is a map of preferred conformations. This is analogous to the Ramachandran plot for peptides (see Figs 4-3, 4-9). The known conformations of the three polysaccharides shown in Figure 7-19 have been determined by x-ray crystallography, and all fall within the lowest-energy regions of the map.

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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