 Hello, today we're going to talk about macromolecules. Macromolecule mean large molecule. Now, whatever is large, it could be anywhere from like 1,000 and many, many 1,000 odd molecules that are connected with chemical bonds so that the whole structure can be considered one large molecule, therefore macromolecules. We are going to focus on large biological molecules. And these are four groups that you really need to know really well. So those are proteins, carbohydrates, nucleic acids, and lipids. Now, regarding another classification, we can say that proteins, carbohydrates, and nucleic acids are actually polymers. Lipids, they're a wide variety of the molecules that are falling into this category. But neither of them are actually considered polymers. So let us see what is the difference between the polymer and monomers. So polymers in macromolecules, polymers are consisting of repeating units of the monomers. It's much like LEGO blocks. If you think about the structure that is made from LEGO, you can take it apart. And you can, again, make something else if you just connect them properly so you have a different structure, but they're made from the same units. Those units are monomers. And you can see here that for carbohydrates, monomers are monoseccharides. For proteins, monomers are amino acids. And for the nucleic acid, monomer is nucleotide. Now, how they are arranged, it can be in different way. You can see here repetitive one single monomer that has one line. It could be in different shape. For instance, you've heard about starch. You've heard probably about cellulose and glycogen. Difference between them is only in the structure. How they are organized in space, who is connected to whom. But otherwise, they're consisting only from one single monomer, and that monomer is glucose. This is very important because in biology, in our systems, in living systems, everything has to do with the shape. And we will talk about that a little bit later when we are talking about the proteins and enzymes. Now, you can see that some of the polymers that consist of similar units. So there is something that is common for all of those units, but there is enough difference that they are different monomers. In this case, the illustration from that could be, for instance, polymer of the polypeptide, which is different amino acids that are linked in one single chain. Now, for all the polymers, how they are put together. Remember, when you have Legos, you need to use some force. In biology, that is done through the enzyme activity. So there is an enzyme that is bringing together something to monomers, and it's taking away something to have that connection. That taking away is actually water, molecule of water. And that would be called dehydration reaction. Again, to separate something, we need to introduce the same molecule of water. So that would be hydrolysis, or breaking down by water. In this case, this is hydrolysis. So we are introducing one molecule of water, which will take OH, will go to one molecule, and the other monomer will receive H. So now we will have separate monomers, separate units, and we have the remnant of the polymer. That is hydrolysis. The opposite reaction is dehydration reaction. That is how we build something. So for instance, you want to be really strong, have those muscles, and you want to go to gym. So you're taking your protein shake and whatever. Yes, those proteins, they are from different sources, sometimes from milk, sometimes from some other sources, soy and so forth. So what you're taking, you're taking the protein. Your enzymes are breaking down all those polypeptides, all those parts of that protein into single amino acids. Those amino acids are then absorbed by our body and then reused to build variety of the proteins that we need for our own functioning. So if you want to build your muscles, you need to actually break down somebody's else proteins and then build your own. How is it done? By dehydration reaction, dehydration reaction. That means taking away OH from one monomer and H from the other to build water and to build the polymer. So let's see how would that look like. We have here amino acids that we obtained through the food that we are taking. One molecule of water is taking away and we have the beginning of our polymer. Of course, this is very much simplified. I'm really asking you to imagine one huge enzyme that is actually taking care that that connection is good, that that is soldering, so to speak, making true chemical bond in between. So continuing, it is happening more and more. So for every connection between two monomers, we have one molecule of water being taken away. Dehydration reaction, D taking away water or condensation. Not every condensation is dehydration reaction, but dehydration reaction falls under condensation. So when you have something that is really sweet and yummy, what do you usually want to do? You're thirsty. You want to have some water. You want to have some drink with it. Now for every single polymer, every single whether it's a desaccharide, so every combination of the monomers, we need one molecule of water to break down that connection. Not to mention that actually everything is happening in the water environment, so we need additional water for that too. But this is a typical example of the hydrolysis. So one molecule of water is introduced, one monomer is released, we're ingesting it. The next molecule of water is introduced, and so forth. What we have to pay attention is when we are drinking something that is really sweet, like a sweet tea or soda or any kind of really sugary drink, we need to introduce more. We need to take more of the pure water just to break down the sugar that is contained in that liquid, in that drink that we took being thirsty. So we will talk more about it in the next chapter, which is carbohydrate. Thank you.