We know that a glycosidic linkage connects two different monosaccharides to one another, but there's also an alpha version and a beta version. Now, here we're going to say this type of linkage is always defined by the linked anomeric hydroxyl group. Remember, your anomeric hydroxyl group is connected to the anomeric carbon, which is carbon number 1 of one of your monosaccharides. We're going to say here alpha and beta linkages are defined in the same way as cyclic monosaccharides. And we’re going to say the exception here is sucrose. It possesses two linked anomeric hydroxyl groups, so both must be named. If we take a look at the different types of glycosidic linkages, let's take a look at maltose. In maltose, we would say that this CH2OH is up, but then the bond here of the anomeric carbon is pointing down. It's on the opposite side. Based on what we know about cyclic monosaccharides, opposite sides mean that it is alpha. So this would be an alpha-1,4 glycosidic linkage. Alpha because it's pointing down, and 1,4 because it's the anomeric carbon, carbon 1, and on the other monosaccharide, carbon number 4, that are connecting together to make my linkage.
Next, we have cellobiose. If we look here, CH2OH is pointing up, and the bond that is connected is part of the linked anomeric hydroxyl group; it's also pointing up. We said that if your OH and your CH2OH are on the same side with each other, that would be beta. The same applies here. So this is a Beta-1,4 linkage for this particular disaccharide. Next, we don't have a 1,4 here, we have a 1,6. So the same rules apply. We look at the anomeric carbon. We look at its linked hydroxyl group. It is pointing down. CH2OH is pointing up. They're on opposite sides. That would mean that it is alpha. So here, we're going to say that amylopectin is going to be an alpha-1,6 linkage because the carbons that are connecting the glycosidic bond or glycosidic linkage are carbons number 1 and carbon number 6.
Finally, we have sucrose. Remember, sucrose is different. We have two anomeric carbons here. So this is the anomeric carbon of this 6-membered ring. And technically here, this is the anomeric carbon of this 5-membered ring. If we take a look here, we would say that this linked hydroxyl group is pointing down and this CH2OH is pointing up. They are on opposite sides of each other, so that would be alpha. And then we say that this anomeric carbon, we're going to say this is carbon 2 in this case. If we look at it this way, where it’s linked hydroxyl group, anomeric hydroxyl group is pointing up, and this CH2OH group is also pointing up, they're both pointing in the same direction, the same side, that would be beta. So here, we'd say sucrose is an Alpha-1,Beta-2 Glycosidic Linkage. So just remember, for the most part, we're following the same rules that we know of in terms of cyclic monosaccharides. With sucrose, it’s just that now there are two anomeric carbons, so you have to name them both: Alpha-1,Beta-2 glycosidic linkage for sucrose.