Biology: Dehydration Synthesis, Hydrolysis

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Recognize this? This is a monosaccharide. Monosaccharides, how important are they in cells? Boy, we are talking about the source of energy, the source of energy right here. This particular monosaccharide is glucose. Now, if you were a call or if you were a plant you would probably want to evolve or design a way to store these things. And, indeed, these are stored. And, they are stored in a form where you put two of these or more of them together. I want to show you this principle of synthesis right now. And, in fact, we'll probably get to the opposite of it, which is hydrolysis or breakdown too. But, what is most important is to realize that without synthesis without the ability to put things together we don't have life. Without synthesis without putting things together life doesn't exist. Synthesis is the secret to life.
Now, let's talk about synthesis. How do you synthesize things and what are we gong to synthesize out of this monosaccharide? Well, monosaccharide, learning that word was easy, the next one is just as easy. We are going to make a disaccharide, two simple sugars. How are we going to do that? Well, we have to come up with a way to manipulate atoms. Remember, the essence of synthesis is bonding. You see, synthesis puts things together and remember that in order to put something together you have to manipulate atoms and expose charges. That is what this is all about. Oh boy, are we going to learn about enzymes because enzymes are the magic to do this, but I'm going to show you how these enzymes do it.
Well, let's take a couple of simple sugars and let's see what we can do with these things. So, we are going to take the shortcut, I'm going to do the lazy mans way and we are going to make our glucose molecules like so. And, I'll try to make it symmetrical. So let's take a couple of these things and let's do an H right here and let's do an OH right here and don't forget our number six-carbon right there. And, just remember that we always are going to number our four, five, and, six - one, two, three, four, five, and six. These are the two though that I want to worry about. Are there hydrogens and oxygens hanging off of here and a carbon up here? Absolutely. Now, one of the nice little things we are doing here is wherever you see a point, unless it is otherwise noted like that's an oxygen, you can assume that those are carbon atoms. And you know that this is a monosaccharide so I think we are all copasetic on this one.
Now, let's take another glucose, it's another monosaccharide so we are going to take another monosaccharide just like this one and now we are going to look at this side. So, just so we have something to refer to, let's throw in those numbers. One, two, three, four, five, six and now we are going to drop this thing right here and we are going to put an HO here, and I'm just reversing the order for that just so I can show you something very cool in a second, and an H here. So, I have an OH group pointing down here on the number four carbon, remember they are here and they are here too, I'm not neglecting them they just are not going to be involved in this particular reaction.
By the way, what I am about to show you is called dehydration synthesis and there are a couple of unbelievably important parts of this I want you to understand. First of all, a synthesis is a making, we are making something. You have heard of photosynthesis, synthesis means to make get that one into your head. Dehydration is easy, this is not like getting thirsty though, we are going to somehow remove water. What I am showing you it is a big picture of something called polymerization. I'm going to come back to this diagram but I want to give you this word polymerization. In this case the glucose molecules are going to be called monomers, mono - one, one mer, one unit. On the other hand we are about to polymerize a molecule called a disaccharide and in that we are going to make a polymer, officially we are about to make a diamer, but there's no officials out there.
So, anyway, here we go. Let's take a look at what is going to happen here. We have our two OH groups hanging off, and I think you have probably already figured out what we are going to do. We are going to take one of these OH groups and we are going to remove a hydrogen from it, like so, dehydration. Recognize HHO, H[2]O, there you go H[2]O we're making water. But, what is that going to leave? What that is going to leave is it's going to leave some very sad molecules, let's see why.
So, here's what we've got. We've got this and this and this and this and this and now what we've done is we have taken H and we've gone like this. And, what we've done is we've removed our OH and that's gone down here we'll make water, OH. So look, there's no one there that is breaking laws. Remember, carbon, each of these is a carbon and carbon has four bonding sites. So, with this whole tendency of atoms to fill their valence shells or to fill in with valence electrons this leaves an unfilled shell here.
So, this carbon has a bonding site this way, a bonding site this way, a bonding site this way, but it is not bound to anything here. Well, meanwhile this carbon or this monosaccharide over here has lost something else. Well, what has it lost? What it has lost is it still has its hydrogen up here, but what it has is it has an O here which lost its little hydrogen to here, HOH water. So, this oxygen, remember oxygen has two free bonding sites, two valence electrons, well, it has one all hooked up right here, but there is no one here to bond to oxygen. What are we going to do? Covalent bonds to the rescue, there is a free bond, there is a free bond, we are going to make a linkage between this and we are going to call that a glycosidic linkage, there's a word you can talk to your family about. Glycosidic - linkage or bridge, let me show you a glycosidic linkage and how this is going to occur done by professionals.
Here we go. So, here's the process that I showed you, but not I've put in all the hydrogens and oxygens so that you can see that I really wasn't lying to you. There's my OH and my H they are popping off and they are forming water, two glucose molecules. Now, we are going to free up some bonding sites. So, we're going to free those bonding sites up and let's see, and then those two bonding sites are actually going to form a glycosidic linkage. There is the linkage guys right here. So, what is going to end up happening is you are going to connect these two things by a bond that goes across and that is the glycosidic linkage. I will draw it for you. So there we go one, two, three, four, five, six, ahh, there's my oxygen it is bridging those, there's my glycosidic linkage, get that hydrogen up there right, and get that hydrogen up there.
Well, what is the opposite of this? What happens when you eat a disaccharide? Sugar, table sugar is a disaccharide what happens when you eat it? You digest it, you break it apart. Well, if dehydration synthesis adds water, oh, it takes water out, oh, I just gave it away. If dehydration synthesis takes water out and makes a bond what do you think you have to do to break that bond? I gave you a clue. You are going to do a process called hydrolysis. Hydro - water, lysis - means to break, water breaking. We are going to take that thing and if I could just reverse this arrow it would be so much fun. But when once that linkage is made, once we have a glycosidic linkage in here, say in this particular molecule maltose, all I have to do now is take water and add it in there. We'll add an H and an OH the molecules will break, what do you get? You get two glucose molecules.
One last thing, does this just happen in monosaccharides? Absolutely not. What I have just shown you is the secret to synthesis. Without dehydration synthesis you don't make molecules. So, whether you are making proteins or anything else you have to dehydrate it to make that linkage. Dehydration synthesis is the secret to life.
Inorganic and Organic Chemistry
Carbohydrates
Dehydration Synthesis and Hydrolysis: Disaccharides Page [1 of 2]