Okay, this video is going to go over the basic introduction to chapter 5, and in chapter 5, this is where we're going to start talking about those biologically relevant molecules, or the macromolecules, that we've been sort of building up to as we've been progressing through this semester. So all of our things are made out of four classes of large biological molecules. These are going to include your carbohydrates, your lipids, your proteins, and your nucleic acids. Remember, nucleic acids are the same thing as your DNA and your RNA.
Now, for the sake of this course, I'm going to categorize all four of these classes of biologically relevant molecules as macromolecules. Macro for big, molecule for molecule. Even though some of the molecules within these four categories might not be macromolecules, not that big, but just for the sake of simplicity, we're going to call...
All four of these categories of biologically relevant molecules, macromolecules. Now, as we have been discussing in chapter four, remember we talked about organic molecules and the fact that they have this carbon skeleton, and attached to the carbon skeleton, you can have a number of different functional and chemical groups. All of these molecules that fall into these four classes of biologically relevant molecules have unique properties.
And these unique properties arise because of their... carbon skeleton as well as those chemical groups that are attached to the carbon skeleton. Alright, now many of these macromolecules are also built as polymers.
And the way that we define a polymer is it's a long molecule that consists of many similar building blocks. These similar building blocks, we give them the name monomers. So mono, one, poly, many. You can use many of the monomers.
to build a really long polymer made from many of the monomers. My analogy here is Legos, right? If you remember playing with Legos as a child, you probably remember having those little, you know, four part square Lego blocks. They come in different colors, right?
Your red, your yellow, green, and blue. All of the individual Lego blocks would be considered your monomers. Now you could take a whole bunch of them, right, and build them all together to form a tower, for example.
And the tower would be the equivalent of a polymer made out of the individual Legos, which are the monomers. Now of the four biologically relevant molecules that we're talking about in this chapter, three out of those four classes, the molecules are built as true polymers, right? So...
These three classes would include the carbohydrates, the proteins, and the nucleic acids. So the one category that is not actually built as true polymers would be the lipids. We're still going to discuss lipids, but again, remember they're not built as true polymers. Now, much like our building blocks, you can imagine that if you have a big pile of Legos, the Legos aren't going to build themselves into a tower. You need some sort of catalyst, some stimulus to get them built, right?
Maybe a four year old. But in the case of cells, right, when you're building these polymers, these big macromolecules, again, you need some sort of catalyst. This catalyst typically comes in the form of an enzyme.
So an enzyme is going to be a specialized macromolecule that's going to speed up chemical reactions such as those that either make the polymer or break the polymers. So this leads us to discussion of what kinds of molecules will make and break the polymers. There's a specific kind of chemical reaction that does each. So anytime you want to make a polymer, you're going to be using a dehydration synthesis reaction.
Typically, when you hear the term dehydration, you would think loss of water, right, or lack of water. That's in fact exactly what happens in a dehydration synthesis reaction. You're going to have...
the linkage of two monomers together to form a covalent bond between them. And this happens through the resulting loss of a water molecule. When you want to break a polymer, you're going to do exactly the opposite. So in this case, you're going to go through a hydrolysis reaction.
Hydro meaning water, lysis, we're going to come back to this term multiple times through this semester, but lysis means to break. So anytime you're going to go through hydrolysis, you're going to use a water molecule. You're going to break it, and at the same time, you're going to use that to break apart monomers from a polymer.
Let's take a look and see what this looks like using actual pictures instead of words. So in this particular slide, we have an example of both a dehydration reaction and a hydrolysis reaction. You'll notice the dehydration reaction up at the top.
So here we're going to have that short polymer on the left-hand side. You can see that it's already built using those three monomers strung together. We want to add a fourth monomer, the unlinked monomer.
In this case, we're building a larger polymer, so we're going to be using a dehydration synthesis reaction. To do this, we need to remove a water molecule. So you'll notice a hydrogen in blue there from the short polymer and a hydroxide from the unlinked monomer.
Those make H2O. So we can remove those atoms out, making a water molecule. And as a result, we're going to link then the third monomer with the fourth monomer, creating a slightly longer polymer, longer by one monomer, four instead of three. Hydrolysis reaction is the complete opposite of this. Here we are going to break apart a polymer and we do so taking one monomer off at a time.
So in this case, hydrolysis requires the addition of water. So you're going to add water in and you end up breaking the water molecule into hydrogen and hydroxyl group. You're going to add those to either the shorter polymer now or the unlinked monomer, sort of satisfying the valence for atoms within both of those two components. Now each cell has thousands of different kinds of macromolecules, and this is really what makes life different.
This is how we show diversity. Now macromolecules are going to vary among cells within one multicellular organism, right? So skin cells are going to have those macromolecules to help it look like and behave like a skin cell versus a muscle cell, for example.
You can even have variability regarding the macromolecules within a species. So this is what makes human beings, makes us all a little bit different. And then obviously macromolecules are going to vary even more when you're looking between species as well.
Now keep in mind that as we start discussing these polymers, we can have a huge variety of polymers that can be built really from just a very, very small set of monomers, right? My Lego blocks, for example, there were four different colored Lego blocks. That's it. That's my set of monomers. But, you know, I can have many, many different ways to combine just four different colored Lego blocks, right?
You could probably create thousands of different towers using those same four colors for the Legos, much like DNA, for example, right? DNA only has four building blocks, A's, T's, C's, and G's. And yet only having that small little set of monomers, we can come up with thousands of different kinds of genes. So it really creates a lot of variability when it comes to being able to build these macromolecules.