 Okay, there's a lot on this slide that I do not want you to know. I don't care about fissure projections, I really care about this except to point out something. This is a monosaccharide, it's called defructose. The way that this molecule is drawn is the carbons are kind of, there are carbons at these intersections, carbons are kind of drawn in a straight line up and down. This is called a fissure projection, but like I said, I don't really care that you know this. This is the way that I have been showing you monosaccharides in a previous video. So for example, I'm drawing more or less fissure projections there. The point that I want to make though is that for most monosaccharides, once they get to about five or six carbons in size, they aren't really arranged like this. They're arranged like this some of the time, but what happens with a lot of monosaccharides is that they wrap around and they make a ring, and I'm going to show you that on the next slide. You can ignore all of this. So here is what I'm calling a fissure projection. Remember I don't really care that you know that, but this is just a way of drawing the molecules where the carbons are kind of arranged in a straight line. Most of the time, monosaccharides are not like this. Most of the time the carbons wrap around, see how the carbons are wrapping around now, and then they wrap around and connect to each other, and this little bit here is called a ring, and for most monosaccharides usually there's an oxygen atom that is part of the ring. So the point is that in one of the earlier videos when I was talking about monosaccharides I said that this was going to be my cartoon for a generic monosaccharide, and the reason is because most of the time the carbons wrap around in monosaccharides and connect to each other with an oxygen somewhere, and traditionally you draw the oxygen at the top of the ring, and if it's unbalanced you usually put it on the right side like that. So that's really the only thing that I'm trying to point out here, is that a lot of times monosaccharides wrap around and make a ring like that, sometimes you will see monosaccharides drawn like this, where the bottom bonds are thickened like that, and they're written in a solid way, and we've already talked about this a little bit. That means that this bottom part of the molecule, especially these two carbons, they're supposed to be pointing toward you in 3D. So just for what it's worth, if you ever see those thickened bonds like that, that's called a Hallworth structure, again I don't really care that you know that name, I do care that you know what these thickened bonds are supposed to be showing you, but I don't care that you know the name. I used to care about something called mutorotation, a whole slide and a whole bunch of gibber jabber about it, but I don't care, ignore it. So we should know, you should be able to recognize a Hallworth structure, not the name, but if I show you something like this, the bottom bonds thickened, and I say this is carbon number one, and this is carbon number two, or whatever, and I say which bonds are pointing toward you in 3D, you should know it's these. You should know that monosaccharides usually make a ring, that's what cyclic means. You should know the wedges are just these thickened bonds, so those thickened bonds are sometimes called solid wedges, but you should know what those thickened bonds mean, it means that those thickened bonds are pointing toward you in 3D, and that's it. Now we're going to move on to disaccharides. So we said in an earlier video that disaccharides are made by connecting two monosaccharides together, that's what the dye means, dye means two. So disaccharide is two monosaccharides bonded to each other. There are many different kinds of disaccharide molecules, maltose is a disaccharide, again I don't care that you know this, I'm just giving you examples. The way that you make maltose is you take two glucose molecules, glucose is a monosaccharide, and you connect them together, you make that disaccharide, if you connect them in a certain way. If you connect them in another way, you might make a different disaccharide. Lactose, you might have heard of people who are lactose intolerant, lactose is a disaccharide, and you make it by taking a glucose molecule, connecting it to another monosaccharide called galactose, that makes a disaccharide called lactose. People who are lactose intolerant are unable to break the attachment between these two sugar molecules. There are other ones. This is the one that you and I eat most frequently. This is called sucrose, we just call it table sugar, and that is a disaccharide that's made from glucose and fructose, which is another monosaccharide. Now in the next slide, I'm going to show you the general way to make the general chemistry of how to make a disaccharide. So how to make a disaccharide. This is just one specific example, but this is generally true. This is a glucose molecule here, this is another glucose molecule over there. Suppose that these two molecules are bouncing around in one of yourselves, and for whatever reason your cell wants to connect them to each other to make a disaccharide. What it can do, there's a carbon here, there's also a carbon here, what it can do is it can rip out that alcohol functional group, that OH, from one of the glucose molecules, and it can rip out a hydrogen from a neighboring glucose molecule. And if I rip those things out, I can use them to make water, because I'm ripping out two H's and an O there. So I'm going to rip them out and I'm going to make water, they're gone. But now these molecules have a problem. This carbon needs an attachment because I just ripped one of its attachments away. This oxygen also needs an attachment because I ripped the hydrogen away. So what your cell can do, is it can connect that carbon to that oxygen. And once I connect them to each other, well I've made a disaccharide, I've made a bigger molecule from two smaller ones. But here it is, here's the connection, here's the water that got made as well, because remember we ripped the pieces of water out and we made a water molecule. So this particular disaccharide, it has a name, it's called maltose. Again, I don't care that you know that. But I do care that you know the general idea of how to connect the molecules. You rip the OH out, you rip the H out, you make a water molecule, and that ends up giving you a bigger molecule when you're done. This kind of reaction has a special name, it's called dehydration synthesis. This is the most common way that living things use to make bigger molecules from smaller ones. In other words, almost, I don't know if it's almost all reactions, but it is many, many reactions in living things. When they have two little molecules that they need to connect to each other to make a bigger molecule, what they will do is they will rip out pieces of water from the two little molecules, make a water molecule, and use the extra attachments that need to get made to connect the little molecules to each other to make a bigger molecule. So dehydration synthesis is what this kind of reaction is called. And just in general terms, that is, in general terms what dehydration synthesis is, the reaction for dehydration synthesis is, you take small molecule one, small molecule two, and then this is an arrow, so this is a chemical equation, ends up making a bigger molecule and you end up making water. So if you have a reaction with water on the right side and you got it by ripping pieces of water off of two smaller molecules and you ended up making a bigger one, that is called the dehydration synthesis reaction. And it is used over and over and over again in biological systems. And I am emphasizing it because I think it's important, so I guess that's a hint. It's also going to show up when we talk about protein molecules. Now once we are done with this chemical reaction, we have this big molecule here and the water goes bouncing around off into the distance. Suppose for whatever reason that your cell, this molecule is bouncing around in one of your cells and now your cell wants to break this apart and get the two little molecules back. Your cell can run the reaction in reverse, in other words it can take a water molecule that's bouncing around nearby, break it apart and add it over here and basically split the attachment and that kind of reaction also has a name. It's called hydrolysis and that's spelled like that. Hydro means water, lysis means destruction, so what it means hydrolysis means destruction of an attachment by adding water back. So if you ever see a reaction like this, water plus big molecule turns into two little molecules, that is going to be a hydrolysis reaction. And this hydrolysis is the most common way that living things use to take big molecules and split them into smaller and smaller pieces. It's not the only way, but it is the most common way. So I want you to know that as well. So here's just another example of dehydration synthesis. If you take glucose, here's glucose. You take another monosaccharide called fructose, there it is, and you want to connect them. One way that you can connect them is you can rip out this OH, you can rip out this H, then this carbon is missing an attachment because we ripped out the OH. This oxygen is missing an attachment because there used to be an H stuck there and we can connect them to each other. And that is just another example of dehydration synthesis. Here's the arrow for the equation. We made water because we ripped out an OH and an H, and then we have this nice connection and we have a bigger molecule now. This is table sugar, this is the stuff that you and I put in our coffee, maybe, if you do that. Alright, so that's an example of dehydration synthesis. That is also two examples of how to make a disaccharide, right? This is a disaccharide, this thing over here is a disaccharide. Just as an aside, you can spend a minute and ask yourself, is this sucrose, is this molecule table sugar, you can compare it to the one over here, maybe spend a minute flicking back and forth. If you notice, it is almost table sugar, but there's some weird things going on. There's a chlorine here, there's a chlorine here, chlorine there, I think there are a few other weird things going on as well, but those are the major ones. Over here, no chlorines. This actually is Splenda. Splenda tastes sweet because it looks an awful lot like table sugar, but it has these other weird things on it, so it's not exactly table sugar, so you can eat it. Your body basically looks at this and says, that tastes sweet, but I have no idea how to break that thing apart, which is why you don't get any calories from it. Alright, what do I want you to know? You should know what a disaccharide is, that's two monosaccharides connected to each other. You should know what dehydration synthesis is. You should know what the reverse reaction is, that's hydrolysis, and that is the end of this video. There's one more video to go, so we'll see you in the next video.