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Polysaccharides, such as starch, chitin, glycogen, and cellulose, can be broken down into monosaccharides. This occurs through the process of hydrolysis, which uses water to break the bonds between monosaccharides.

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  • primosaur tree style avatar for user 115450-Tomas
    Since the wings of a Fly are made out of strings of starch, and starch can be broken apart by water how come the wings do not get destroyed by water?
    (27 votes)
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  • duskpin ultimate style avatar for user Chang Huang
    This might be a stupid question but since everything we saw in this video(Cotton, Wins of insect...) are pretty much just glucose, in an emergency case, can we eat them to get energy?
    (18 votes)
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  • blobby green style avatar for user Sarah Opst
    At , Sal mentions that the carbon is very willing to release the oxygen and bond to the water molecule. I understand that the oxygen also is eager to break a bond because it normally only has two, and currently it has three with two carbon bonds and one hydrogen bond. But if the water molecule floating around bonds to the carbon, causing the carbon to release the other oxygen from its bond, the oxygen of that water molecule is also forming three bonds. This puts it in the same place as the oxygen which had just broken off. I don't understand how the carbon is more likely to bond to a water molecule and release the other oxygen rather than just keep the other bond intact considering that in both cases, an oxygen is in the situation of having three bonds? I hope this makes sense. ; )
    (11 votes)
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    • blobby blue style avatar for user Angel
      The Oxygen with the "+" is positively charged after bonding with the "H+". When it breaks off with the carbon, it takes the carbon's electron (from the covelant bond) away, allowing the oxygen to become nuetral again (now it has 8 electrons: 2 old valence, 2 new valence from the C-O bond it just broke, one from O-H, and one from remaining O-C). The Hydrogen is also nuetral because it has one electron from the O-H bond. Then the "broken" carbon bonds with the water molecule to complete its octet.
      (7 votes)
  • leafers tree style avatar for user Julie Trisel
    Why don't all polysaccharides, such as cellulose, taste sweet?
    (10 votes)
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    • leaf green style avatar for user Ashley  He
      Great question!

      As you may know, different receptors on the tongue produce different tastes of sweet, sour, salty, and bitter. The receptors that produce the sweet taste only bind to monosaccharides or disaccharides, such as glucose, sucrose, or fructose. However, the receptors do not bind to polysaccharides.
      (2 votes)
  • starky tree style avatar for user Amyntas
    In , Sal mentions that it took the water molecule to break up the bond and turn the chain into individual glucose molecules. Is this why being dehydrated (i.e. not drinking enough water) can be fatal, because our body can't break down the polysaccharide chains into glucose without water?
    (9 votes)
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    • winston baby style avatar for user Ivana - Science trainee
      There are many reasons and things which are more severe and lead to death than being unable to break down glucose during dehydration.

      1. Severe dehydration leads to electrolyte disbalance. Cell content becomes hypertonic and there is not enough water which cell can soak in order to create balance. Since potassium and sodium are imbalanced then your neural system suffers and you have seizures. Electrical impulses are messed up.
      2. Low blood volume. Low blood volume causes a sudden drop in blood pressure and drops in the amount of oxygen in your cells therefore you die.
      3.Kidney failure. Your kidneys are unable to remove excess fluids since there is no water to be expelled via urine. While minimal excretion is 1500ml a day, if you stop drinking water, your body is unable to produce even that 1500mL.
      4. Overheating. Dehydration makes it impossible to sweat and cool your body.

      Every single bodily function requires water! So before digestion takes place, the overall disbalance of electrolytes and low blood volume are the first to kill you due to dehydration.
      (6 votes)
  • aqualine ultimate style avatar for user gingerchemistgirl
    [at mins] is there any reason the arriving water molecule will prefer to bond to either side of the linking bond between the monomers?
    Is the -O- bond in the leftmost monosaccharide withdrawing electrons enough to influence the behaviour of the arriving water molecule?

    (I hope this makes sense)
    (9 votes)
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  • blobby green style avatar for user Sylvain Liu
    Hi, I don't really get why the oxygen acquires a positive charge when it bounds to a hydrogen. Since oxygen is more electronegative than hydrogen, shouldn't the charge of the oxygen atom be partially negative?
    (6 votes)
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  • duskpin ultimate style avatar for user Arki🖤
    At , Sal mentioned that in cellulose the glucose molecules get flipped over. Why is that?
    (5 votes)
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    • marcimus pink style avatar for user isa bel
      It flips because the OH groups need to align. If it didn't flip they wouldn't and the glucose molecules simply wouldn't bond. It wouldn't be starch however, because starch bonds with alpha glucose where the OH already aligns ( on C1 and C4 ) but cellulose bonds with beta glucose where the c1 OH goes up and the C4 goes down. It needs to flip to align
      (4 votes)
  • blobby green style avatar for user SandyMcNaul
    Is the saliva in our mouths involved in dehydration reactions or hydrolysis reactions? And why?
    (4 votes)
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  • hopper cool style avatar for user 🤔 ᴄᴏᴅᴇᴅ ɢᴇɴɪᴜȿ 😎
    Sal said that Hydrolysis is using water to break something down, but in his diagram, there are the two glucose molecules and a water molecule (the H₂O below the two). Would that mean that if two glucose molecules bonded together wouldn't they just break themselves apart because of the water molecules that is there?
    (4 votes)
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    • winston baby style avatar for user Ivana - Science trainee
      No, not that easy. Hydrolysis of polysaccharides is not spontaneous and favorable process.

      In starch (or any other kind of polysaccharide) two glucose monomers are bonded via a glycosidic linkage which is a very strong bond. That bond itself makes O and C from two glucose molecules inaccessible and invisible for the present water molecule. Polysaccharides have strong and consistent structures being hard to dissolve in water.
      (1 vote)

Video transcript

- In the video on dehydration synthesis, we saw how we could start with a glucose molecule, and through dehydration synthesis form a bond with another glucose molecule. And just by doing that, you'd form the disaccharide maltose if these were both glucose molecules. But then you could keep going, and you could form longer chains of glucose molecules. And to these things, where you would take a monosaccharide, glucose is the most common example of that, and you create chains of these, we call these polysaccharides. Polysaccharides, this is a polysaccharide. And there's all sorts of interesting examples of polysaccharides all around you, especially polysaccharides of glucose, or things that are derived from glucose. This right here this is a bowl of mashed potatoes, which is mostly starch. Which is mainly just chains of glucose. So this right over here, that is starch. The shell of a lot of insects and things like lobsters, and the wings of these insects right over here, that's made of something called chitin. And chitin is also a polysaccharide. It's made of chains, a modification of glucose chains of that, that's chitin right over there. Very similar to starch, in our muscles we have glycogen, which is our store of energy in our muscles. You have cellulose, which is probably all around you right now. Cellulose are things like-- Because this is something that's all around you, and you don't even realize it. Cellulose, this is what constitutes things like paper and wood. It's involved in the cell walls of plants. This right over here is a picture of cotton, cotton in its natural form. And cotton is actually one of the purest forms of cellulose, it's roughly 90 percent cellulose. And if you take a zoom in on a cotton fiber, actually a fiber of cellulose, you'll see chains of glucose molecules. So you see this right over here, that is a glucose molecule. Then you see another glucose molecule. And this chain has been formed through dehydration synthesis. And difference between starch and cellulose, for the main difference, in terms of how this bonding has. With starch, the glucose molecules just keep forming the way that you saw in the video on dehydration synthesis. While in cellulose, they get flipped over. So you can see here, this oxygen is pointing that way, this oxygen is pointing that way, that oxygen is pointing that way. And you could look up more about cellulose. But it's really interesting, what gives it its structure are these hydrogen bonds that form between the partially negative, the very electronegative oxygens on one strand. And the partially positive hydrogens on another strand, and that's actually what give its structure. So really, really interesting things, these polysaccharides. The question is, how do you actually break these things down? If I were to eat these mashed potatoes, how do I eventually turn this thing into glucose, so I could use it for energy? And the way that happens is through hydrolysis. And you could break down this word. The "hydro", if you see hydro, the prefix hydro, that's a good clue that it has something to do with water. And then if you see "lysis", if you're lysing something, this means that you're gonna break it down. So this is breaking down something using water. And that's exactly what happens with hydrolysis. If you have this polysaccharide, and let's throw a water molecule in there, this water molecule is going to be able to break one of these bonds. So we might end up with something like-- This chain could keep going in both directions, but we could end up with something that looks like this. That looks something like that. So half of this water molecule gets broken up, essentially to break this bond. It's the opposite of dehydration synthesis. So let's see if we can understand, get an overview of exactly how that happens. So this right over here, this is maltose right over here. It's disaccharide, it's just two glucose molecules attached to each other. If we kept doing this, if this kept going, if this guy had bond to another glucose molecule, and this guy had a bond to another glucose molecule, then we'd be dealing with starch. Or we could be dealing with glycogen. If this was flipped over, and they kept flipping over and over, then we could be talking about cellulose. But let's just thing about how this is the mechanism. The mechanism by which this bond can actually be broken. It's really just the reverse of dehydration synthesis. This is going to just be an overview of it. This oxygen right over here, it's got two lone pairs. There's always a chance that if it bumps into something in just the right way, it could nab a hydrogen proton that is just sitting out there in the fluid. We're assuming that this is happening in an aqueous solution, it's happening in water. So it can just grab a hydrogen proton from a passing hydronium molecule. And so if it does that, it would form a covalent bond, and have a positive charge. And now relative to actually both carbons, but let's focus on this carbon right over here. This guy would be, what we call in organic chemistry, a good leaving group. So these electrons, the oxygen might want to just take these back, because it's got a positive charge, oxygen is really electronegative, so things just bump in exactly the right way. If things interact in exactly the right way, you might have another water molecule. And this is where that extra water molecule is valuable in our hydrolysis. So let's say this is just another water molecule just passing by in exactly the right way. This could form a bond with that carbon right over there. And just as it forms a bond with that carbon, the carbon says, "Okay, I'm getting to share "some other electrons, let me let go of these electrons." So it lets go of these electrons. And what do you have left? Well, we can go over here, and so now this carbon has, let me color code it, so this bond that was just forming, that is this bond right over here. This oxygen is this oxygen right over there. It actually has another hydrogen attached to it, so let me do that. So right when it makes the bond, it will have a positive charge. And then, this bond right over goes back to this oxygen. This oxygen right over here, is that oxygen right over there. Now when it started off, this guy grabbed-- The hydrogen proton that I grabbed, I showed in orange, that's this one. That's this one right over here. Now, this one grabbed a hydrogen proton, and now this one can actually give back a hydrogen proton through solution. If a water molecule passing by could just grab this hydrogen proton and then become a hydronium molecule. So it took a hydrogen proton, it's giving it back, and so what we are left with-- It took up this water molecule right over here to break the bond. And so this is a positive charge. It could be a passing hydronium molecule, and it'll just hand it off to that. And there you have it, we have two standalone glucose molecules right over there. We have broken the bond. And these could be parts of chains, in which case, we've just broken the chain. Or, if we're just dealing with maltose, now we've broken it down into the individual glucose molecules. And the example here is with glucose, but it could've been the case with maltose, and it could've been the case with sucrose where we break sucrose down using hydrolysis into a glucose molecule and a fructose molecule. So it's a very important reaction in biology.