Disaccharides: Difference between revisions
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== Maltose and Cellobiose == | == 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 structures you can observe that both have a 1→4 glycosidic bond<ref>[http://en.wikipedia.org/wiki/Glycosidic_bond Glycosidic bond]</ref>. 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. 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. Both structures show the anomeric carbon (green) of the second glucose unit as the α 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<ref>[http://en.wikipedia.org/wiki/Reducing_sugar Reducing sugar]</ref>. | |||
<Structure load='Maltose.pdb' size='400' frame='true' align='left' caption='' scene='Disaccharides/Maltose/1' /> | <Structure load='Maltose.pdb' size='400' frame='true' align='left' caption='' scene='Disaccharides/Maltose/1' /> | ||
Revision as of 22:24, 8 November 2011
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 CellobioseMaltose 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 structures 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. 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. Both structures show the anomeric carbon (green) of the second glucose unit as the α 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].
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