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Carbohydrates- di and polysaccharides

Video transcript

all right so in a previous video I talked about how cyclic monosaccharides like this green the screen cyclic glucose can react with alcohols like this pink alcohol to form asset Al's and key towels and I believe that I mentioned that that sometimes the alcohol that comes in and is reduced is actually another carbohydrate so let me kind of draw this in here and it makes sense because what you see with carbohydrates is that they're chock full of hydroxyl groups they're chock full of these Oh H groups and and so really they can function really similarly to alcohols and reactions and when this happens the individual monosaccharides are linked together to make an acetal and we call this linkage a glycosidic linkage so this is a glycosidic a glycosidic linkage now when two monosaccharides are linked together in this fashion by by glycosidic linkages we call a product a disaccharide die a disaccharide and we have die 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 anomeric carbon or or c1 so remember this is the anomeric carbon that's c1 so over in the in our glycoside here B right here just the same we've got C one of the first sugar and then C four of the second sugar so right here would be C four and it's just the same over here so right here we have C four and that's the second sugar so we call this a 1-4 glycosidic linkage and then just like we could further break down our monosaccharides into alpha and beta based off the orientation of the other animerica Doxil group we can more specifically call the 1 4 linkage an alpha or a beta linkage again based off what is now the orientation of the Larr group on the anomeric carbon so same rules apply if the if the group is sis with respect to the sixth carbon its beta and of course if it's trans it would be an alpha linkage so in this case we are our oor group which the O our group is this whole carbohydrate is sis with respect to the c6 carbon so we have a beta one four glycosidic linkage and if that bit of naming confused you a little bit I went over that in greater detail in a different video but what I want to focus on here are some of the common disaccharides so let me clear some space let me give us some room I'm going to go ahead and fade in a drawing that I did a little bit ago to save just a bit of time and what we have here is a disaccharide you see two two carbohydrates two monosaccharides linked together and this one happens to be lactose which you might be familiar with so lactose and lactose happens to be really the principal disaccharide found in in milk and that's actually true for both human milk and for cow milk and unlike really most disaccharide lactose isn't really appreciable sweet it consists of one galactose so this one right here is galactose and then one glucose carbohydrate and they're bound together by a by a 1-4 glycoside bond just like we saw before so we've got the the one and the four and this is a glycoside bond and this one happens to be in the beta orientation select oh s--- is a disaccharide made of galactose and glucose joined together by a beta 1-4 glycosidic bond os-- so let me write that in here we've got maltose and and 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 in their bow together similarly by a14 glycoside so we've got the one carbon right here that's this one and we've got the four carbon over here so 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 oo r group ii ii carbohydrate which is functioning as the o r group is in the trans position with respect to the first carbohydrates six carbon over here so this is an alpha 1-4 glycosidic linkage and it binds together on two glucose units so that's maltose so another pretty common a disaccharide and then last but not least let me pull in here for you sucrose and 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 at a table sugar which comes from sugar cane so sucrose is actually quite sweet but it's different substantially so from maltose and lactose and I want to point out a couple of the key differences so in lactose and maltose both of these appear you have two Piron OSes remember pure noses are six membered carbohydrate rings I went over that in a previous video but we we have two six-membered rings bound together by this glycoside and in sucrose that's different we've got a six membered glucose right here this is this is glucose bound to a five membered or a furanose fructose oh we got fructose right here so so fructose and what happens is you have both of the the carbohydrates linked together by their animerica Arbenz so right here we've got two in america Arbenz linked together now that's different than maltose and lactose so for example right here is the anomeric carbon have both maltose and lactose it's over here that's the ceefor that's bound so this are these are both linked together by their in americ-aa r bonanza have two acetal thats that are formed so we've got an acetal right there and remember an acetal is when a carbon is linked to an O R group over here and an O R group over here and then you have a second asset al at the fructose Asst and Emeric carbon and so with maltose and and and the same thing with lactose you have a hemiacetal x' that are formed so you've got an asset al right here and then you've got a hemiacetal over kind of on the tail on the second glucose that's a Hemi a hemiacetal and that you can look at and it's the exact same thing for for lactose but what happens here is remember that with a hemiacetal you can add on a second Oh H group to form another asset Allah he me asset al can be further reduced into an asset al but once you have an asset al you can't further reduce it so that makes sucrose a non reducing sugar and then lactose and maltose are both reducing sugars and so lactose maltose and sucrose are probably the three most common disaccharides and they give us a good basis for disaccharides and then really polysaccharides are just an extension of this thought so let me clear some space and 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 kind of pre drawn in another drawing here let me make a little bit more rhythm for it and that's what I've shown here I've shown just kind of the addition a couple additions of extra carbohydrates onto disaccharide so both of these have three the carbohydrates and you could keep going but that's what makes them polysaccharide so this first one that I drew in is a polysaccharide called cellulose and cellulose is found in the cell walls of really nearly all plants and it gives support and structure to wood and to plant stems and and really cotton is essentially just pure cellulose but cellulose is that is that polysaccharide made of repeating glucose units that are joined together by beta 1-4 glycosidic bond so all of these are beta 1-4 glycosidic linkages and and really this it forms an unbranched just kind of straight change and that's the polysaccharide cellulose now down here I have another polysaccharide which is also super common and this is starch and you can see that that really this is this is made up of repeating again repeating glucose units here the difference is that these linkages are alpha still 1-4 so still one four linkages but these are alpha units and 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 and 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 1-4 glycosidic linkages of glucose so we can't appreciate we use cellulose as an energy source and then one less excuse me one last polysaccharide that I want to show you is really very similar to starch so I'm going to use the starch as little basis here but if you if you kind of branch off of the starch every once in a while on the c6 carbon so that's the c6 carbon right here and you add on another glue so I'll start there this is another another glucose you can keep going with alpha 1-4 excuse me alpha one four linkages again and you can form essentially just branches branches so this one would go here and then you could maybe down the line here have another one and so these are these are mostly 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 and so if it's highly branched we caught what we call it glycogen and that's a little bit a little bit dumb down above concept but essentially that's what glycogen is it's it's a major polysaccharide made of alpha one four linkages with with that are heavily branched by these alpha one four one six excuse me brakes but glycogen and it's it's significance for us is principally as a source of storage of energy so 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 to get a fast glucose source so that's probably the a good a good start for polysaccharides as well we've got cellulose which is beta one four linkages of glucose and stretching we've got starch which is essentially kind of a chain of alpha one four linkages of glucose and then we've got glycogen which is really really similar to starch except that there are there are alpha one six linkage breaks in here that that enable us to form kind of chains of this polysaccharide