Name the glycosidic bond present in mannobiose, shown in the following figure:

Question

Structural representation of mannobiose, highlighting the glycosidic bond between its two sugar units.

Accepted Answer

Hi, everyone. Our next problem says, identify the gly acidic bond present in lactose. So we're given the structure of lactose, which we can recall is made up of galactose and glucose. And then we have four answer choices for the name of this bond choice. A alpha, 1 to 4. So one arrow four glyco cytic bond B beta, 1 to 4 glyco cytic bond C alpha, 1 to 6 glycolytic bond or D beta 1 to 6 glyco bond. So we actually already know that only one of our sugars here is going to be linked by its anomic carbon because you need to designate alpha or beta for every anomic carbon that's in the linkage. And when we look at our structure, we see that our sugar mal sugar on the left, which happens to be galactose does have its anomic carbon. So I put a little pink dot there in the gly acidic bond and then on our glucose, I'll put a pink dot on that carbon. So let's figure out which carbons are involved here. So we know that uh the anomic carbon is in between the two oxygens, the ring oxygen and then a second oxygen from a hydroxyl group. So that's carbon one. And then in our glucose on the right, find the anomic carbon, which is number one. So our anomic carbon is over on the right. And then let's number our carbons going around the ring 234. So we see that it's carbon four involved in the linkage, not carbon six because carbon six keep going around, the ring is external to the ring. It's linked to carbon five and coming up out of the plane of the ring. So we can eliminate choices C and D which have the second carbon as being carbon six of glucose rather than carbon four. So now we just need to determine whether this is an alpha or beta linkage. So going back to our galactose on the left, we have to compare the positions of the oxygen that was in the hydroxyl group and is now in the linkage on carbon one. And then the position of the group attached to the stereo center, carbon or carbon five on the other side of the ring oxygen. So in this case, as so often, that group will be the C H2O H that includes carbon six and that is coming up above the plane of the ring. And then our oxygen and linkage is also coming up above the plane of the ring. So these two groups are sis to each other. They're on the same side. I put this, they're on the same side of the ring. And I always remember it by writing same, the word same starts with a consonant like B for beta. So if those two groups are on the same side of the ring, that is a beta linkage because that hydroxyl group on the an americ carbon was in the beta position. If it were pointing down. And so therefore opposite to that C H2O H, then it would be an alpha gly acidic bond. So cross out choice A and we know that our answer must be choice B and the glyco cytic bond present in lactose is beta 1 to 4 gly acidic bond. See you in the next video.

Name the glycosidic bond present in mannobiose, shown in the following figure:

Verified video answer for a similar problem:

Key Concepts

Glycosidic Bond

Mannobiose Structure

Disaccharides