Hi everyone welcome back. In this lecture we're going to be looking at the four classes of biological macromolecules, and one by one we're going to talk about how they are structured and what sort of role they play inside of living organisms. We're going to be discussing carbohydrates, lipids, proteins, and nucleic acids. Here is just a cartoon image of each of the macromolecules and you can see lipids are made up of glycerol and these fatty acids. Here we have carbohydrates. You can see these individual rings glucose rings. You can see nucleic acid. These are nucleotides. And proteins, the subunits are amino acids. Once carbon containing molecules with functional groups had appeared early in earth's history, we can ask ourselves, well what happened next? And for chemical evolution to continue these small organic molecules had to form larger more complex molecules like those that we find in our living cells. These large molecules are made up of smaller molecular subunits joined together and they are called macromolecules. A molecular subunit used to build a macromolecule is called a monomer. A monomer is a single molecule that can be combined with similar molecules to create larger structures. You can think of this Lego brick. When monomers are bonded together, the resulting structure is called a polymer. The process of linking monomers together is called polymerization. Amino acids produced from the Miller-Urey experiment are a great example of monomers that polymerize to form proteins. How is it that these individual monomers become linked together? Monomers polymerize through condensation reactions also known as dehydration reactions. These reactions are named this way because the newly formed bond results in the loss of a water molecule. Here we see a generic polymer on the left and an unlinked monomer, this would be the building block of whatever it is we're building. Here on each end you have a hydrogen and an -OH group. Let's take a moment and in your notebooks: what functional group is the -OH group? What is the name of this functional group? We have this functional group, our OH group here. I'm going to wait a few moments before revealing this. and here's our unlinked monomer which has a hydrogen on this side. The unlinked monomer will release the proton, and the short polymer that we're building into a longer polymer is going to release the OH group. Here you can see that we're removing water. Hence the name dehydration reaction, and a new bond is formed from this part of the polymer and this one. And this reaction is done over and over and over. So this -OH group will be released if another monomer is coming in with an H, another water molecule is removed and then you would have an added subunit. Let's watch a short video to make sure we have this concept down. This video is also going to include hydrolysis. And hydrolysis is the reverse reaction that breaks polymers apart by adding a water molecule. The water molecule reacts with the bond that links the monomers, separating one monomer from the polymer chain. Many important biological molecules are made of repeating subunits called monomers. When many monomers join, the result is a polymer. For example, amino acid monomers joined to form a protein polymer and glucose monomers combine to form a complex carbohydrate polymer. Biological polymers formed by dehydration synthesis reactions, as you can see here, each of the monomers in this reaction has a hydrogen or H and a hydroxyl or OH group. In the course of the reaction, the hydrogen is removed from one monomer and the hydroxyl group from the other. The hydrogen and hydroxyl group combine to form water and a bond links the two monomers. Hydrolysis is the opposite of a dehydration synthesis reaction. During a hydrolysis reaction, a polymer is reduced to its monomer's subunits by the addition of water. In fact, the word hydrolysis literally means to break water. The hydroxyl group from a water molecule attaches to one monomer and the remaining hydrogen attaches to the other monomer. In other words, water is used to break the bond holding monomers together. Let's do a quick recap. During dehydration synthesis, monomers joined to form polymers and water is released. The opposite happens during hydrolysis where water is added to the reaction to break a polymer into monomers. Both dehydration reactions that link monomers to form polymers and hydrolysis, a reaction that breaks polymers apart, are all mediated by enzymes. If you recall enzymes are made up of proteins most part most enzymes are proteins you pro there's always exceptions to the rules but most are proteins. Enzymes help to speed up chemical reactions or orient the atoms in such a way that the reaction will take place. In this short animation you will observe how an enzyme helps to facilitate the reaction. The purple is the polymerase, ends with ase. That's a clue that it's an enzyme and it helps to orient those molecules so that they come together to do the reaction. This is hydrolase this is a different enzyme. We're adding water so that the molecule is split. This is just a reminder, we've talked about how amazing it is that so much is made from such a limited set of molecules. A cell makes a large number of polymers from a small group of monomers. For example, proteins, we only have 20 different amino acids but we have thousands of different proteins. DNA is built from just four kinds of nucleotides and it's the sequencing that allows for the diversity that we see. The monomers used to make polymers are essentially universal.