ID #1100

Do all beta 1-4 linkages cause alternating glucose molecules to be at 180 degree turns to each other? The cellulose picture indeed represents this pattern, but the picture of cellobiose does not (lecture 3)

That's a good question. There is a difference between the way chemical structures can be drawn and how they "look" in real 3-dimensional space. As it turns out, when glucose molecules are hooked together in beta 1-4 glycosidic linkages, in 3-D space, they DO rotate 180 degrees when each new monomer is added. The reason the illustrator of that cellobiose figure chose not to show it this way was just for simplicity. There's no way that you would be expected at this point to see that figure and interpret how the molecules take up real space, but a more experienced student of carbohydrates would look at this figure and recognize that the bonds between those two monomers would have to "zig-zag" in order to join, and this is only realistically going to be possible if the monomer "turns."

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