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Video transcript

in the previous video we talked about the importance of glucose as a simple sugar we talked about its molecular structure what I want to do in this video is study how glucose can be can how we can use it as a building block for more complex sugars and more complex carbohydrates so this right over here I have copy and pasted two glucose molecules you can we can number their carbons this is one two three four five six one two three four five six we have them in their cyclical in their cyclic form and we're going to do is explore what would happen if this oxygen right over here I'll highlight it in this magenta color we're to use one of its lone pairs one of its lone pairs to do a nuclear what's in organic chemistry referred to as a nucleophilic attack on the number one carbon on the left-hand glucose molecule and the reason why that could happen is this number one carbon right over here it's attached to two oxygens oxygens are very electronegative they like to hog electrons when they're in a covalent bond so that's going to give this carbon a partially positive charge and this oxygen is very electronegative it's going to hog the electrons from this hydrogen and this and the number four carbon on the right-hand glucose molecule so it's going to have a partially negative charge and so it is going to be nucleophilic it's going to be attracted to I guess you could say the carbon nucleus to the two then the partially positive charge right over here and so as it does that's going to form it's going to use a lone pair to form a bond it's going to share it with the carbon and then the carbon can let go of another bond so it could let go of it could let go of the of both of these electrons in that bond now you could say oh maybe that just goes back to the oxygen and it forms a hydroxide anion or we could imagine well maybe it maybe it'll be used you maybe you know it maybe it forms a hydroxide anion first or maybe that bond immediately goes and picks up a hydrogen ion out of out of the solution from from another from a hydronium from a hydronium ion sitting someplace so this can be used this can be used to form a bond with hydrogen ion which is really is this is just a proton here you take an electron away from hydrogen it's just going to be a proton well what's that going to do well that's going to link these two glucose molecules and it's going to link it it's going to link it just like this and it's important to keep track of our our molecules here so this oxygen is now going to be this oxygen is now going to be that oxygen this bond between the number four carbon on the right hand side and that oxygen is this bond right over here this this when we took this this electron pair to form this bond with the number one carbon that is that is let me do it in that magenta color that is this bond this bond right over here the oxygen this oxygen is now this oxygen right over here and these this electron pair is now formed a bond with this hydrogen so we could say well that could be that could be let me do that blue that could be that could be this hide that this could be this bond right over here now the one difference is based on how I've drawn it this oxygen or sorry this oxygen the way I've drawn it it's attached to the number one carbon here the number four carbon here we have that over we've already done that in four here number one carbon on the Left molecule number four carbon on the right molecule but we also have it bonded we also have it bonded to a hydrogen so just the way I've done it right now it's still bonded to a hydrogen it's going to have a net positive it's not good it's going to have a net positive charge over here it was neutral it was neutral right over here but then it it it's now sharing its electrons it's now sharing both of those electrons in a covalent bond and so you can think of think of it as giving it it's given in a way it's giving away an electron to this carbon so it's going to have a net positive charge but then to get back to neutral you could imagine well maybe maybe some some type of a a water molecule could could grab that ion so this maybe this one right over here this one right over here could grab could grab that hydrogen and then these electrons of them and it would just grab the hydrogen nucleus at the proton and so these two electrons could go back to this oxygen and then become this oxygen would become neutral and so what we would be left with what would be what we would be left with actually let me just erase this is that this hydrogen this hydrogen would now be attached it would now be attached to this oxygen and we would have a hydronium hydronium ion and this is reasonable we we essentially had some hydronium we had a hydrogen proton out here before and we still do now it's attached to a water so we haven't you know we've we've taken a proton and we've given back a proton so we haven't you know net net kind of added charge or taken charge away taking charge away from the system but the important thing that we just saw is as these two things as these two things essentially attached we lost we lost a water molecule or I guess net net this system lost a water molecule it took it it took up a charge and to do it to build that water molecule but the thing that really kind of escaped from both of these two molecules is is this is this is this right over here this H is this H this oxygen is this oxygen and this hydrogen is this hydrogen right over here and so this type of a reaction in which we are synthesizing a more complex molecule a longer chain of a longer chain of glucose of glucose molecules this is called a dehydration synthesis so what we just did this right over here is called a dehydration dehydration synthesis why are we calling it a dehydration synthesis well we've just taken a water out if you imagine losing water we talked about that's you're getting dehydrated so this and why synthesis well we put two things together we synthesized a larger molecule sometimes this would be this would be called a condensation reaction con Condon condensation reaction and by doing this these two glucose molecules are able to form a disaccharide now so each individually each individually they were monosaccharides so this one on the right that's a mono monosaccharide what does monosaccharides mean well it means mono means single or or one and saccharide comes from the Greek word for sugar the Greek word for sugar is I'm going to mispronounce it is saccharine when people talk about something being saccharine they're taking something that's very very sweet the Greek word for sugar is saccharine it's so saccharide means it's a sugar it's a single sugar so that the meaning there is sugar and the general term saccharide refers to not just these simple sugars monosaccharides but it could mean it could mean two of these put things put together and there's other simple sugars fructose and and others or it could mean a huge number of these put together you could have polysaccharides and that whole class saccharides these we also associate with carbohydrates now this now we went from two monosaccharides to right over here this is a disaccharide this is a disaccharide we have two two monosaccharides were involved this is a disaccharide and this particular disaccharide is maltose or malt sugar maltose maltose so the whole point of this video is to see how you can start with these simple sugars these monosaccharides and form disaccharides in fact you could keep going you could keep having dehydration synthesis condensation reactions to keep adding more and more monosaccharides to build longer and longer chains so if you were to keep doing that if you were to keep building chains of these things now you're getting into the now you're getting into the world of polysaccharides poly saccharides or many simple sugars money monosaccharides many monosaccharides put together and this is a case for sugar but since this is something that you'll see often in chemistry where you have a single unit here it's a single sugar but if we talk in more general terms we would call it a monomer monomer and then if we have a bunch of these monomers put together we would call it a we would call it a polymer now polysaccharides are super important and you have probably eaten some polysaccharides today and you probably have some poly in fact I'm sure you have some polysaccharides stored in your cells right now if you put a bunch of glucose molecule to keep this process going and we were posed and and we would have a bunch of glucose molecules together when you find it in in plants it'll often be in the form of a starch so a polysaccharide that you'll find in a plant is a is a starch a bunch of glucose is put together in your own cells and to have a immediate energy store a bunch of glucose is put together is glycogen is glycogen so these these macromolecules these polysaccharides that are made up of a bunch of a bunch of simple sugars a bunch of monosaccharides put together these are very common in biology you have eaten them and you are storing them in your body right now
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