- Nucleic acids, lipids, and carbohydrates questions
- Nucleic acid structure 1
- Antiparallel structure of DNA strands
- Saponification - Base promoted ester hydrolysis
- Lipids - Structure in cell membranes
- Lipids as cofactors and signaling molecules
- Carbohydrates - Naming and classification
- Fischer projections
- Carbohydrates - Epimers, common names
- Carbohydrates - Cyclic structures and anomers
- Carbohydrate - Glycoside formation hydrolysis
- Keto-enol tautomerization (by Sal)
- Disaccharides and polysaccharides
Created by Ryan Scott Patton.
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- Does anyone know to what extent this will be tested on the MCAT?(4 votes)
- There is a good chance that you will get a question on this type of material. I would suggest learning a lot about carbohydrates as it relates to metabolic pathways.(10 votes)
- For the maltose, isn't the hydroxyl group on C4 for the glucose on the left supposed to be pointing down equatorially, instead of axial-up?(5 votes)
- So what is the name of the glycosidic bond in sucrose?(4 votes)
- For sucrose, the bond is made between the OH on the first (1) carbon of a-D-Glucose and the OH on the second (2) carbon of B-D-Fructose. So, the bond name in sucrose is a,B-1,2-Glycosidic bond. Hope that makes sense!(3 votes)
- For the maltose, I think you drew an alpha galactose linking with another alpha glucose. Shouldn't it be two glucose linking together?(4 votes)
- 8:08So sucrose cannot react to form a polysaccharide? Or can it still react with another sugar's anomeric carbon? (Meaning just the anomeric carbons of the sucrose molecule can no longer react to form a longer chain but the hydroxyl groups can react with other anomeric carbons.)(3 votes)
- Sucrose cannot react to form a polysaccharide because both of its anomeric carbons are acetals. An anomeric carbon that is part of an acetal cannot reduce any further. Sucrose would be a non-reducing sugar.(3 votes)
- why is sucrose, glucose-&-1,2-fructose? thats why i started watching this video but didn't get my answer. how is that the second carbon on the fructose?(3 votes)
- I know this was posted a while ago, but I'm going to try to answer it. :) So, the OH on the anomeric carbon is pointing downward on Glucose, so glucose is alpha-glucose. If you look at fructose, you can see that coming off the anomeric carbon is both an OH and a CH2OH. The CH2OH is the first carbon (just like the CH2 off of the fifth carbon is the sixth carbon): you want the longest continuous chain of carbons. Hope that helps!(3 votes)
- At 0745, Ryan says that an additional -OH group can be added to a hemiacetal; reducing it to an acetal. I believe this is incorrect. I think that to form an acetal an additional -OR group would need to be added and this would oxidize it to an acetal. Correct?(3 votes)
- I'm confused about figuring out if a dissacharide is alpha or beta. I thought if the second sugar was above the joining oxygen it was beta but in the video he mentions cis trans. Could you explain? thanks!(1 vote)
- Lemme see if I can help...when you're looking at a monosaccharide in the Haworth projection (as shown in the video), you want to look at the OH group on C-6....see how it's pointing up and in the equatorial position (slanted line)?
For a cis (same side) BETA (think "birds fly up") your anomeric carbon (C-1) on that same monosaccharide should be attached to another monosaccharide in the SAME/CIS manner as the C-6's OH, which would be pointing up and in an equatorial position.
For a trAns (opposite side) ALPHA (think "little fish swim down") it would be pointing downward and in an AXIAL position attached to the other monosaccharide.(3 votes)
- Do the glycosidic linkages have to be 1,4' bonds?(1 vote)
- There are 1-6 linkages too but they're mostly found in polysaccharides that have branches like glycogen, and amylopectin, the breaches are joined by the 1-6 glycosidic bonds.(2 votes)
- I notice that the glucose molecules in Cellulose have their anemeric hydroxy group and 4 hydroxy groups up and down but between molecules but because the molecule is drawn in a linear fashion (as apposed to slopping) they are classified as a Beta linkages. I don't fully understand how they are both up?(1 vote)
- [Voiceover] All right. In a previous video, I talked about how cyclic monosaccharides, like this green cyclic glucose, can react with alcohols, like this pink alcohol, to form acetals and ketals. I believe that I mentioned that sometimes the alcohol that comes in and is reduced is actually another carbohydrate. Let me draw this in here. It makes sense, because what you see, with carbohydrates, is that they're chock full of hydroxilate groups. They're chock full of these OH groups. So, really, they can function really similarly to alcohol in reactions. When this happens, the individual monosaccharides are linked together to make an acetal. We call this linkage a glycosidic linkage. This is a glycosidic, a glycosidic linkage. Now, when two monosaccharides are linked together in this fashion, by glycosidic linkages, we call the product a disaccharide. A disaccharide. We have "di," which means two, and "saccharide," which means sugar. So sugar. So two monosaccharides linked together, they're called a disaccharide. Now, with disaccharides, most commonly the glycosidic linkage forms between the anomaric carbon, or C1 ... Remember, this is the anomeric carbon. That's C1. Over in our glycosite here, it'd be right here, just the same, we got C1 of the first sugar. Then, C4 of the second sugar, so right here would be C4, and it's just the same over here. So right here we have C4. That's the second sugar. So we call this a one, four glycosidic linkage. Then, just like we could further break down our monosaccharides into alpha and beta based off the orientation of the anomeric hydroxyl group, we can more specifically call the one, four linkage an alpha or a beta linkage, again, based off what is now the orientation of the OR group on the anomeric carbon. Same rules apply. If the group is cis with respect to the sixth carbon, it's beta. Of course if it's trans, it would be an alpha linkage. In this case, our OR group, which the OR group is this whole carbohydrate, is cis with respect to the C6 carbon. So we have a beta one, four glycosidic linkage. If that bit of naming confused you a little bit, I went over that in greater detail in a different video. What I wanna focus on here are some of the common disaccharides. Let me clear some space. Let me give us some room. I'm gonna go and fade in a drawing that I did a little bit ago to save just a bit of time. What we have here is a disaccharide. You see two carbohydrates, two monosaccharides, linked together. This one happens to be lactose, which you might be familiar with. Lactose. Lactose happens to be really the principal disaccharide found in milk. That's actually true for both human milk and for cow milk. Unlike, really, most disaccharides, lactose isn't really appreciably sweet. It consists of one galactose. This one right here is galactose. Then one glucose carbohydrate. They're bound together by a one, four glycoside bond, just like we saw before. So we've got the one and the four. This is a glycoside bond, and this one happens to be in the beta orientation. So lactose is a disaccharide made of galactose and glucose, joined together by a beta one, four glycoside bond. Now, next up we have maltose. Let me write that in here. We've got maltose. Maltose is, again, a disaccharide. But this time, it's made of two individual glucose units. So we've got a glucose right here and we've got a glucose right here. They're bound together similarly by a one, four glycoside, so we've got the one carbon right here, that's this one, and we've got the four carbon over here. This is, again, a one, four glycosidic linkage. But, as opposed to lactose up here, this one's actually alpha. You can see that this OR group, this second carbohydrate, which is functioning as the OR group, is in the trans position with respect to the first carbohydrate's six carbon over here. So this is an alpha one, four glycosidic linkage and it binds together two glucose units. So that's maltose, another pretty common disaccharide. Then, last but not least, let me pull in here for you sucrose. Sucrose is actually probably the most common disaccharide in all of nature, and you deal with it quite frequently, I'd imagine, because sucrose is the principal disaccharide of table sugar, which comes from sugar cane. So sucrose is actually quite sweet. But it's different, substantially so, from maltose and lactose. I wanna point out a couple of the key differences. In lactose and maltose, both of these up here, you have two pyranoses. Remember, pyranoses are six-membered carbohydrate rings. I went over that in a previous video. But we have two six-membered rings bound together by this glycoside. In sucrose, that's different. We've got a six-membered glucose right here ... This is glucose ... Bound to a five-membered, or a furanose, fructose. So we got fructose right here. Fructose. And what happens is, you have both of the carbohydrates linked together by their anomeric carbons. Right here, we've got two anomeric carbons linked together. That's different than maltose and lactose. For example, right here is the anomeric carbon of both maltose and lactose. It's over here. That's the C4 that's bound. These are both linked together by their anomeric carbons. What happens is, you have two acetals that are formed. So we've got an acetal right there. Remember, an acetal is when a carbon is linked to an OR group over here and an OR group over here. Then you have a second acetal at the fructose's anomeric carbon. With maltose, and the same thing with lactose, you have hemiacetals that are formed. So you've got an acetal right here and then you got a hemiacetal over on the tail, on the second glucose. That's a hemiacetal. You can look up and it's the exact same thing for lactose. But what happens here is, remember that with a hemiacetal, you can add on a second OH group to form another acetal. A hemiacetal can be further reduced into an acetal. But once you have an acetal, you can't further reduce it. That makes sucrose a non-reducing sugar. Then, lactose and maltose are both reducing sugars. Lactose, maltose and sucrose are probably the three most common disaccharides. They give us a good basis for disaccharides. Then, really, polysaccharides are just an extension of this thought. Let me clear some space. For those reducing sugars, like maltose and lactose, that are left with a hemiacetal group at the end, we can keep adding sugar groups onto the chain. That's kind of this reducing characteristic. They can keep growing, which ends up making more acetal groups, but always leaving a hemiacetal group on the end. So I've kind of pre-drawn in another drawing here. Let me make a little bit more room for it. That's what I've shown here. I've shown just the addition, a couple additions, of extra carbohydrates onto disaccharides. Both of these have three carbohydrates. You could keep going. But that's what makes them polysaccharides. This first one that I drew in is a polysaccharide called cellulose. Cellulose is found in the cell walls of really nearly all plants. It gives support and structure to wood and to plant stems, and, really, cotton is essentially just pure cellulose. But cellulose is a polysaccharide and made of repeating glucose units that are joined together by beta one, four glycosidic bonds. All of these are beta one, four glycosidic linkages. And really, it forms an unbranch, just kind of straight change, and that's the polysaccharide cellulose. Now, down here, I have another polysaccharide which is also super common. This is starch. You can see that, really, this is made up of repeating, again, repeating glucose units here. The difference is that these linkages are alpha. Still one, four. Still one, four linkages, but these are alpha units. Really, the functional difference here is that, as humans, we have the enzyme to break down these alpha one, four linkages and we can use starch, which again is found in a lot of plant products, as a source of energy, because we can break these down into glucose to undergo cellular respiration. But we lack the enzyme to break down the beta one, four glycosidic linkages of glucose, so we can't appreciably use cellulose as an energy source. Then, one last ... Excuse me. One last polysaccharide that I wanna show you is really very similar to starch. I'm gonna use the starch as a little basis here. But if you branch off of the starch, every once in a while on a C6 carbon, so that's the C6 carbon right here, and you add on another glucose. I'll start there. This is another glucose. You can keep going with alpha one, four ... Alpha one, four linkages again, and you can form essentially just branches. So this one would go here, and then you could maybe down the line here have another one. These are mostly alpha one, four linkages. Every once in a while, you get an alpha one, six linkage thrown in there, ' which creates some significant branching. If it's highly branched, we call it glycogen. That's a little bit dumbed down of a concept. But essentially, that's what glycogen is. It's a major polysaccharide made of alpha one, four linkages that are heavily branched by these alpha one, six breaks. But glycogen, it's significance for us is principally as a source of storage of energy. We can build glycogen stores in our body and it creates a really functional store of glucose because, with all these branches, we have a lot of tails of glucose that can be chopped off pretty quickly to get a fast glucose source. That's probably a good start for polysaccharides, as well. We've got cellulose, which is beta one, four linkages of glucose in a straight chain. We've got starch, which is, essentially, a chain of alpha one, four linkages of glucose. Then we've got glycogen, which is really, really similar to starch, except that there are alpha one, six linkage breaks in here that enable us to form chains of this polysaccharide.