Consider the trisaccharide A, B, C shown in Problem 20.23.
c. State the numbers of the carbon atoms that form glycosidic linkages between monosaccharide A and monosaccharide B.

Question

Consider the trisaccharide A, B, C shown in Problem 20.23.

c. State the numbers of the carbon atoms that form glycosidic linkages between monosaccharide A and monosaccharide B.

Accepted Answer

Hello, everyone. And welcome back. Our next problem sets, considering consider the following trisaccharide. And we have a structure of a trisaccharide drawn for us three monosaccharide units labeled A B and C. And then our problem says, determine which carbons form the glyco cytic bond between monosaccharide units A and B. So we don't, we can just ignore mono sacry at sea uh and focus on A and B. We see that both of them. In fact, all three are in a pinos form. So a six membered ring and let's look at this bond we're focusing on, I'm highlighting a pink that would be the bond where the oxygen connects the two rings in between A and B. So our first step because we need to determine which carbon. Well, how do we do that? We have to number the carbons so we can label them. So to number the carbons, we need to find the anomic carbon on both rings. So I'm going to erase the highlighting of the glycolytic bond and highlight the anomic carbons. This is because we number carbons starting with the anomic carbon in the ring. That's number one. And then we go around our ring away from the oxygen in the ring. So looking at monosaccharide, A, look for the oxygen, the ring, look at its two neighboring carbons and find the one that has two carbons connected to it, called our anomic carbon is the carbon that has two oxygens bonded to it. So that would be the carbon to the far right of the ring on mono sac ride A now looking at monosaccharide B, find the oxygen in the ring, look at its neighbors and find the carbon that's connected to two oxygens. In this case, it's also in the far right on the ring. So both of those will be carbon number one in their rings. So starting with monosaccharide, a label, carbon one go around the ring away from the oxygen of the ring. So we're going uh clockwise to carbon 2345 and then carbon six is above the plane of the ring. That's C H2O H group monosaccharide B is going to be similar. So carbon one on the right are anomic carbon and then proceeding clockwise, carbon 2345 and six out on top of the plane of the ring. Now, we need to look at where the glyco cytic bond is. That's that bond that links the two ring, that glyco bond will always form between the anomic carbon of one ring and the hydroxyl group of the other brain. That's because the gly acidic bond forms between A hemi acetyl or hemi ky or when that he ayl or hemi kyl group, I should say reacts with a hydroxyl group of another molecule. So in terms of looking at uh polysaccharides or trisaccharide, in this case, the gly acidic bond will always be between carbon one of one ring. So we start with carbon one. So I'll put C one of monosaccharide A. So I'll highlight that number one in yellow. And then we see that that gly acidic bond goes to carbon four of monosaccharide B. So we're not asked about whether it's an alpha or beta bond just to be really thorough here. If you wanted to, you could look and see that this bond goes above the plane of the ring of monosaccharide A. Therefore, it's on the same side of the ring that C H2O H group, that carbon six group, they're both above the plane of the ring. They're on the same side of the ring. And therefore there's a beta gly bond, but we don't actually have to answer that for our question. So what we are asked is which carbons form is quite acidic bond between monosaccharide units A and B. And that would be carbon one of monosaccharide A with carbon four of monosaccharide B. See you in the next video.

Consider the trisaccharide A, B, C shown in Problem 20.23.

c. State the numbers of the carbon atoms that form glycosidic linkages between monosaccharide A and monosaccharide B.

Verified video answer for a similar problem:

Key Concepts

Glycosidic Linkages

Monosaccharide Structure

Trisaccharides