Disaccharides
From Proteopedia
The objective of this article is to illustrate and visualize the structures and concepts of disaccharides[1] that are difficult to visualize and illustrate by viewing two dimensional structures in textbooks.
Maltose and Cellobiose
Maltose (α-D-glucopyranosyl (1→4) D-glucopyranose) () and Cellobiose (β-D-glucopyranosyl (1→4) D-glucopyranose) ( are both disaccharides made of D-glucopyranose. Comparing the two structures given below you can observe that both have a 1→4 glycosidic bond[2]. C-1 (orange) of one glucose unit is bonded to the oxygen of C-4 of the second unit. The difference between the two is that maltose is α(1→4) and cellobiose is β(1→4). As you study the two structures notice that with cellobiose the second glucopyranose unit is rotated 180°, so that the oxygen bonds of both C-1 (β configuration) and C-4 of the second glucopyranose unit are projecting up so that oxygen has its normal angular geometry. In order to see the second glucopyranose in its normal position, rotate cellobiose 180° about the x axis so that C-6 is in the back of the ring and projecting upward. Both structures show the anomeric carbon (green) of the second glucose unit as the β anomer, but in an aqueous solution that designation would not be significant because there would be an equilibrium mixture of the α and β anomers and the open-chain structure. The open-chain structure in an aqueous solution provides an aldehyde group which can be oxidized, so maltose and cellobiose are reducing sugars[3]. Also, notice the sharp bend in the maltose at the glycosidic bond. Most text books do not represent the structure of maltose in a way that shows this bend. View this or in spacefill. This kink produced by the α(1→4) glycosidic bond plays an important role in the structures of polysaccharides that have α(1→4) linkages.
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Proteopedia Page Contributors and Editors (what is this?)
Karl Oberholser, Alexander Berchansky, Jaime Prilusky, Karsten Theis
