Transcription
Okay, so we have looked at molecules um quite a bit in this class now. We've looked at structural formula, molecular formula, and we've looked at um functional groups. So here are some bigger, more complicated molecules. Um, and there's a word up here that says um, get my pencil going, um, macromolecules. The word macro means big, so macromolecule just means a big molecule. So proteins, um, many carbs, fats, they all fall into this idea of being large molecules. They're macromolecules.
Now, this one at the top here, this is cholesterol. We'll dive into this later on in this unit. Cholesterol. And um, a couple things here. So, what, how do I know that this is a molecule? Well, we should have learned already that molecules always have covalent bonds holding the atoms together. And do we see covalent bonds here? Yes, we see lots and lots of these solid lines linking this thing up. So definitely covalent bonds going on here, so definitely this is a molecule.
Now, you might look at this and say, "There's no atoms. This is just shapes. Like, what's going on here?" So, one of the things that happens in organic chemistry is that the molecules that we work with in biology get to be very large. And so we have some shorthand things that we do to make it easier to write them down. So every time you see a change in direction of a line, so like when this one changes direction here and it goes down here, there is a carbon atom that they've missed out on this molecule. Anytime there's a change in direction, and any time you have a junction where lines meet, so here one, one, two, three, and four lines are all meeting here, what that's basically telling us is that there should be a "c" there, and they're just not writing it in. So all across this diagram, there's lots of carbons that are there, but they're just shorthanded out and they don't put them in to make this look a little cleaner. Otherwise, if you put them all in, like I'm doing, it gets to be very busy and complicated to look at. But I'm going to put them in for now because you guys probably aren't used to seeing these kinds of diagrams. So everywhere here is "c", "c", "c". All right.
So that's one thing to be aware of. Whenever you see one of these structures drawn out and there's a bunch of gaps or just no letters, they're assuming that you know that there's carbon at all these intersections and zigzags. So there's another question though here. Carbon, which you should already know, creates four covalent bonds, like this. So because it needs four electrons to fill its shell. So here's a, there's a molecule of methane, carbon with um, four "h"s. Um, so every carbon atom has to have four bonds. And if we look at this, we're like, "Well, okay, this carbon here is only got one bond going this way and one bond going that way." So is that really carbon? Because it, it's supposed to make four and it's only showing two. What they do in these kinds of situations is this: any, any bond that they're not showing you, they're assuming that you know that that is a bond to a hydrogen. So there should really be a line to an "h" here and a line to an "h" here. All right.
So this carbon here, look, this carbon's got one bond going this way and one bond going that way. It's only two bonds. So there's two missing. So we're gonna, we need to put an "h" here and an "h" here. All right. Same here. This carbon has only got two, one, two. So we need to put two "h"s. And this carbon, it's got one, two, three. So it's missing one to get up to four. We need to put an "h" here. So you can see if I put all the carbons and all the hydrogens in, it gets very, very busy and very, very complicated and hard to look at, which is one of the reasons why we just have the shorthand. We miss out the carbons and just put zigzags and and junctions. And then we miss out anything, any "h"s, um, because we assume that you know that if you're, if you're looking at a structural formula, the only reason you'd be doing that is that you know what you're looking at and you know that there's supposed to be "h"s there.
So this zigzag up here is a "c", a "c", a "c", a "c", and a "c" right here. And then there's uh one, two, three. One, two, three. So there's one "h" missing here. There's two "h"s missing there, and there's two "h"s missing there, and there's two "h"s missing there. All right. So I'm trying to draw them in. And this carbon's got one, one, two, three, so four. And the fourth one, and there's an "h" there. All right.
So anyway, just a little quick review of how molecules are drawn out. Um, so this cholesterol molecule up here, we call it a macromolecule. It's pretty big. There's lots of atoms. There's lots of bonds as it's spreading out. When is something big enough to be called macro? Uh, well, if there's no real actual cut off, but, um, you know, if there's like seven, eight, nine bonds, it gets to be kind of big and sprawling, then you can call it a macromolecule.
Now, down the bottom, I have a another molecule called a polymer. Now, this is also a macromolecule. So cholesterol, this is a macromolecule, and this molecule here is also a macromolecule. Both of these are huge, big molecules, so we can call them macro. Right? But this one at the bottom, this green one, we're gonna call it something else as well. It is a polymer as well. And what this means, a polymer is a kind of molecule that is very long and chainy. It's like a chain where you have the same thing, the same kind of um, building block or pattern repeated over and over and over again, like beads on a string or um, carriages in a train.
So if we look at this um, diagram here, this green hexagon, it's a molecule with "c"s in it. You think you can't see the "c"s. They've missed them out. I'll put some in here. Right, these little hexagons. There's a, a bunch of them, the same thing over and over and over and over and over again. This motif is repeating over and over again. So is this a big molecule? Yes, it's huge. So we can call it a macromolecule. But we can also give it another name. We can say, "Yes, this is a molecule that we see a repeating pattern over and over and over, and it's like a long chain." So we can call it a polymer. Poly means many, many repeated things. A polymer.
This one up here, the cholesterol, this is not a polymer. There's nothing here that repeats. Because I've got a hexagon and then a hexagon with a double bond, that's different. I've got a pentagon here. I've got a chainy piece up here. There's no real repeating pattern going on. So while this one is big at the top, it's not a polymer. This one at the bottom is both big and a polymer. So just so you can get used to how these words work.