The objective of this article is to illustrate and visualize the structures and concepts of common polysaccharides[1] that are difficult to visualize and illustrate by viewing two dimensional structures in textbooks. Structures with a 3D perspective are used to illustrate features of a molecule which can not be easily visualized using 2D structures.
Unbranched chain, α(1→4) glycosidic bondsAmylose is an example of a polysccharide which contains thousands of glucoses connected by α(1→4) glycosidic bonds. The initial view (Reset initial scene) shows an eleven unit segment of amylose with yellow halos marking some of the oxygens which form the 1→4 glycosidic bonds. Rotate amylose to view the glucopyranosyl units on edge to see that the bonds are α linkages. (Remember: With the glucose providing C-1 on the left, the glucose providing C-4 on the right and C-6 of the glucoses projecting to the back of the screen both bonds of the oxygen of the α linkage project down.) From this perspective you are looking down the axis of a helix that is formed as a result of the angle that is form between the glucopyranosyl residues when they are connected by the α(1→4) bonds. This characteristic of the α(1→4) bond was seen when studying maltose. Color ends of the polymer yellow and green. Amylose with 20 glucose units; Spacefill display Branched chain, α(1→4) glycosidic bondsAmylopectin is also a large glucose polymer that has α(1→4) glycosidic bonds connecting the glucose units, but it also contains α(1→ 6) glycosidic bonds. In this scene the main branch is colored yellow, the side branch is green and the oxygen atoms of the α(1→4) bonds are red. Rotate Amylopectin to view the glucopyranosyl units on edge and verify that the bonds are α linkages. Glucose unit four, branching point, colored yellow with the oxygen atom connecting C-6 of unit four to the C-1 of the side chain colored green. The reducing terminus is colored CPK, C-1 of this unit is able to open to the aldehyde and function as a reducing agent, but all the other termini of an amylopectin molecule are non-reducing because the C-1 of these terminal units are involved in glycosidic bond and can not form the aldehyde. In this scene the non-reducing termini are colore green. The native amylopectin having many more branching points would be more open than this structure, in fact it would have very little curvature. Rotating & zooming amylopectin gives a focused view of the α(1→ 6) bond. TextToBeDisplayed
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This page was last modified 18:01, 26 January 2012.