Hi, and thanks for tuning in. Today is the first in a series of videos where we are going to discuss biological macromolecules. Biological macromolecules are essential for all living systems. They consist of carbohydrates, nucleic acids, lipids, and proteins. In this video, we're going to introduce ourselves to what these four types of biological macromolecules look like, the types of chemical reactions that allow them to be produced and be broken down, and we'll talk about what a polymer is. So stay tuned. Hi, and thanks for tuning in. Today, we're going to be talking about biological macromolecules. We're going to introduce ourselves to what a biological macromolecule is, how they're made, and how they're broken down. So first, let's talk about what a biological macromolecule is. Biological macromolecules are large molecules that are found in all living systems, and in fact, are responsible for a lot of the way biological systems behave. In fact, without them, life as we know it could never exist. They're the molecules that make up plasma membranes. They're the molecules that make up cell walls. They're the molecules that help to perform essential chemical reactions or store genetic information so that they can be passed on to future generations. Without these molecules, life as we know it could never exist. So what are these biological macromolecules? Well, biological macromolecules are largely classified into four broad categories, lipids, carbohydrates, nucleic acids, and proteins. And what's interesting is, three out of those four classes are what we refer to as polymers. Polymers are substances that are chiefly made of repeating subunits or similar subunits that we refer to as monomers. And of the four major classes, carbohydrates, nucleic acids, and proteins are all classified as polymers. On the other hand, lipids are not. In other words, lipids do not consist of monomeric repeating subunits. So briefly, let's discuss what the monomers for each of those three remaining classes actually are. So for example, carbohydrates, carbohydrates are our fancy word in science for sugars. Now large complex carbohydrates like polysaccharides, which are the polymers, consists of repeating subunits of something called monosaccharides. So the monomer for a carbohydrate is a monosaccharide, the most common of which is glucose. nucleic acids, on the other hand, are polymers that consist of nucleotide monomers. The ones you're probably most familiar with are the A, C, G's, and T's that make up DNA. Adnan cytosine, guanine, and thymine. There's also a fifth one called uracel that exists only in RNA and actually takes the place with thymine, but we'll talk about that later on. Proteins are polymers that consist of monomers called amino acids, which are joined together in different combinations to give each protein its unique composition and its unique structure, which in turn gives it its unique behavior. Lippets on the other hand have no monomeric subunit. They're kind of a mess. They're not repeating and it's easy to describe as, for example, a carbohydrate might be where it just consists of long chains of glucose, something like glycogen, for example. But regardless of whether or not a biological macromolecule is a polymer or not, the types of chemical reactions used to make these is remarkably consistent. And what's interesting is it kind of goes back to the central molecule of water. So one of the things we need to talk about and kind of remind ourselves of is remember that most biological macromolecules are going to have some type of functional group on the end of it, and it's the reaction of these functional groups that allow the creation or enablism or biosynthesis of these biological macromolecules. The type of reaction that's used to make a biological macromolecule is what is known as dehydration synthesis, also known as a condensation reaction. Now as the name implies, this chemical reaction is going to lead to dehydration. It is going to lead to the release of water. And one great example to demonstrate how this works is what happens when we build a triglyceride. So a triglyceride is a combination of a glycerol head group and fatty acid tails. Traglycerides are the type of fatty acid that we try to find in circulation in human beings. If you ever have to go for a lipid panel, when you get old like me, you go to the doctor and they draw your blood when you get a physical and they want to know what your triglyceride levels look like. Now if you look at the structure, you can see that there's that glycerol head group, and then there are three long fatty acid chains that come off. But in order to make this molecule, we have to do something called a dehydration synthesis or condensation reaction. And here's an example of how it works. Now note, when you look at the glycerol head group, you will note that this is clearly an alcohol. Notice our three hydroxyl groups that are coming off of the three central carbons. Also note, at the end of the fatty acid tail, we have our carboxyl group. Notice where we have the carbonyl and the hydroxyl coming off in the remaining R group is that long fatty acid tail. In order to combine these two molecules to synthesize or begin synthesizing a triglyceride, what's going to happen is this. An enzyme is going to come in. It's going to remove one of the hydrogen atoms from the hydroxyl group on the glycerol. It's also going to remove completely the hydroxyl group from the carboxyl group on the end of the free fatty acid. That will allow that carboxyl group to now attach to the remaining oxygen of the hydroxyl group on the glycerol. Now, what you should be realizing is that in dropping a single hydrogen atom from the glycerol, as well as the OH from the carboxyl group of the fatty acid, we've released two atoms of hydrogen in one of oxygen. In other words, we've released a molecular equivalent of water. In fact, the byproduct of this enzymatic reaction is to release water. Now to make a triglyceride, we need to do this two more times. It's the same reaction that occurs where we release one hydrogen atom from the hydroxyl group of the glycerol and the complete hydroxyl group from the carboxyl region of the fatty acid. In the end, we end up with a glycerol group with three fatty acids yielding our triglyceride. Now, to be clear, if we were doing this to create a protein or to create a carbohydrate or to create a nucleic acid, it would basically be the same. There would be different enzymes involved, different substrates involved, but the end result is the release of water and the biosynthesis of a large biological macromolecule. But what happens when we want to break one of those fats down? Or we want to break down a carbohydrate or anything else that's created through dehydration synthesis? Well, the answer is simple. We use a different enzyme that will add the water back in for us. We are going to use water to break down this molecule. If we go back to our Greek words, we will end up with the word hydrolysis or water cutting or water breaking. And that's indeed what happens. An enzyme will come in. It will interact with this biological macromolecule. It will replace the hydroxyl group on the end at the end of the carboxyl, on the fatty acid in this case or whatever molecule we're dealing with. And it will replace the hydrogen on the hydroxyl group of the glycerol, replacing the water and separating the fatty acid from the glycerol. Now, what you should notice, every time we do one of these reactions, first and foremost, we need to use an enzyme. Enzymes are actually proteins. They are protein catalysts. They are the things that exist in all living cells to make chemical reactions like these happen at a rate that is compatible with life. In other words, these reactions would happen likely over time eventually, but so slowly that life wouldn't be able to function. Enzymes make this possible. Also understand that each type of chemical reaction is going to require a different type of enzyme. Enzymes are highly specific with respect to the substrates or the chemicals with which they interact. So, for example, we are going to have to use an acid transferase to make that triglyceride, but we'll use a different enzyme called a light paste that will break down that triglyceride. It performs different reactions on different substrates. If we were doing it with, say, a nucleic acid, for example, we might be talking about something called DNA polymerase that can come in and synthesize new DNA by combining the proper nucleotides. So, today, we just did a short video to discuss the types of chemical reactions that make biological macromolecules, i.e. dehydration synthesis, and the types of chemical reactions that break down biological macromolecules hydrolysis. Remember that water is the central atom to all of this. If we're making a biological macromolecule, we're going to remove water. If we are going to break a biological macromolecule down, we are going to replace that water. This is all going to involve protein catalyses called enzymes. There'll be a series of videos coming out soon where you'll be able to look at each of these individual biological macromolecules, we'll learn what their specific jobs are in the cell, what they look like, and how they behave. Thanks for tuning in, and I hope to see you guys real soon.