Polysaccharides: Difference between revisions

Amylose is a polymers containing thousands of glucoses connected by α(1→4) glycosidic bonds.  The initial view shows yellow halos marking some of the oxygens which are involved in the 1→4 glycosidic bonds. Rotate the structures (<scene name='Polysaccharides/Amylose2/1' target=0>Amylose</scene>, <scene name='Polysaccharides/Amylopectin2/1' target=1>Amylopectin</scene> to view the glucopyranosyl units on edge to see that the bonds are α linkages. 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 [[Disaccharides|maltose]]. Rotate amylose to give a <scene name='Polysaccharides/Amylose3/1' target=0>side view</scene> of the helix and color the first glucopyranosyl in the polymer yellow and the last one green, the only one whose anomeric carbon has the potential to form a reducing aldehyde group. The yellow ring is the last one in the chain, so between the yellow and green rings the first turn of the helix overlaps with the second turn. The yellow end of the chain is the non-reducing end and is the growing end - the end at which glucose unit are added to increase the length of the chain.

 

 

  (Return to) Amylopectin initial view also shows the α(1→ 4) bonds, but its structure is more complex because it also contains α(1→ 6) glycosidic bonds. The structure shown here has only one such bond (yellow halo on carbon #6), in order to keep the structure relatively simple. The green ring is the reducing end of the molecule. The chain that proceeds from the branching point is colored blue. The yellow rings are the non-reducing ends of the two branches. They just happen to be close to each other in this model. The structure is more open (helix is not wound as tight) than the amylose because more space is needed for the chain that is formed at the branching point. 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.