Amylose

Amylose is a linear polymer of glucose that occurs in starch. It occurs in foods such as grains and potatoes, and it is a major source of energy (calories) in most diets. There are three major forms of crystalline amylose, A, B, and V, that differ in the three-dimensional structure. Amylose can also occur as amorphous structure, for example in starch or when cooked in water. Amylose is distinct from amylopectin, which is a branched polymer of glucose, and from 5jiw, which is a linear polymer of glucose that differs in stereochemistry from amylose. In the context of naturally occurring starch, parts of amylopectin form semi-crystalline layers resembling amylose A or B, while amylose itself occurs in the amorphous parts.

Structure

spinqualitylabelsall models Caption for this structure Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Amylose A and B occur as parallel double-helices of glucose chains, with 6 glucose units per turn. In contrast, amylose V occurs as a single helix as shown in the figure (same structure shown as cartoon). A more irregular conformation of a cyclic amylose occurs is found in complex with a protein in the structure 5jiw. In solution, amylose occurs as flexible hydrated single helices. These can bind to small molecules to form inclusion complexes such as the famous starch/iodine/iodide complex. Because of the difficulty in characterizing non-crystalline or semi-crystalline polymeric materials with complex chemical makeup (variation in chain length and location of branch points), the structure of starch and its components is less well characterized than that of proteins.

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