Polysaccharides

The objective of this article is to illustrate and visualize the structures and concepts of common polysaccharides 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.

spinqualitylabelsall models Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Unbranched chain, α(1→4) glycosidic bonds Amylose is an example of a polysccharide which can contain up to several thousand 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. In addition to this native helical structure amylose can accommodate other helical forms Branched chain, α(1→4) glycosidic bonds Amylopectin 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. Looking down the axis of a 20-unit chain (colored CPK) having a 5-unit chain (green) branching at unit five and a 10-unit chain (yellow) branching at unit 10. The red atoms in the yellow and green branching chains are the oxygen atoms of the α(1→4) glycosidic bonds. Structure rotated 90 deg. Notice that the helical structure is more open than the unbranched amylose and the previous structure having only one branch. The native amylopectin having many more branching points would be more open than this structure, in fact it would have very little curvature. The reducing terminus is colored white and the non-reducing termini are colored orange. In a native amylopectin molecule the distance between the branching points is 12 to 30 glucose residues which is a greater distance than in this model, and there would be many more branched chains so that the non-reducing termini would greatly out number the one reducing terminus. Another example of a branched chain polysaccharide is glycogen whose major difference from amylopectin is 8 to 12 glucose units between branching points. Unbranched, β(1→4) glycosidic bonds Cellulose is a polysaccharide with glucose units connected only by β(1→4) linkages, and therefore is unbranched. Segment of cellulose chain Show second chain

Pages of Other Carbohydrate

• maltose
• Disaccharides

Proteopedia Page Contributors and Editors (what is this?)

Karl Oberholser, Karsten Theis