Botany online 1996-2004. No further update, only historical document of botanical science!

Glucanes Containing alpha - glycosidic Linkages

Starch: alpha - 1 > 4 linkages are most common in starch though 1 > 6 linkages do occur, too (P. KARRER, 1921). Depending on the size of the molecule and its amount of 1 > 6 linkages, it is distinguished between amylose and amylopectin. Amylose molecules are largely unbranched, water-soluble and contain mainly 1 > 4 linkages. They are, like most polysaccharides, polydispers, meaning that the length of the molecule is not exactly defined, the number of glucosyl residues being between 200 and more than 1000.

© Thomas A. NEWTON

© Thomas A. NEWTON

The pyranose ring occurs usually in the boat conformation. The alpha - 1 > 4 linkages cause the helical structure of the polysaccharide chain. The inner diameter of the helix is big enough for elementary iodine to become deposited forming a blue complex (evidence for starch). Amylopectin is characterized by branchings. 2000 to 200,000 glycosyl residues form a molecule. alpha - 1 > 6 links occur on average at every 20th residue. Starch occurs in layered starch grains within cells. Their structure is specific for the respective species.

© Peter v. Sengbusch - Impressum