So another way you can kind of differentiate the chemistry we're talking about in biology from the chemistry you're talking about in chemistry is that in biology, we're always focused on what's called organic, almost always focused on what is called organic molecules. An organic molecule is just any molecule that contains the element carbon. So in this recording, we're going to talk about why carbon is so special for helping facilitate life and why it's such, it's so abundant in living things. So the table I showed you in the first recording, that was breaking down the elements in their abundance in humans. If we look at the abundance of these elements in all living things on the planet, carbon is by far the most abundant.
It makes up about 52% of all living things in the world. So why then What is so special about carbon that it is leaned on so heavily by living things? So first, carbon has a neutral electronegativity.
As a result, it can form covalent bonds with a lot of different other elements. It can form covalent bonds with low electronegative atoms. It can form covalent bonds with...
pretty high electronegative atoms. And in order to become stable, carbon needs four electrons, which means it's almost always going to form four covalent bonds. This allows you to build more complex structures, right?
If you think about oxygen, for example, and if you were to replace oxygen with carbon in this laser in this small molecule so oxygen it needs two electrons so you know it can it can bind a couple of hydrogens and make water but you can't really build much more off of that if instead you were to bind oxygen to another oxygen Well, that's going to form the double bond, and then those two oxygen atoms can't make any more bonds. With carbon, it can bind three hydrogens and still be able to bond another carbon. And as a result, you can string multiple carbons along, connected, and also attract bonds with...
other atoms. Expanding on that, if we look at a simple CH4 molecule, we have a carbon at the center and then nonpolar covalent bonds to four hydrogens. This is a stable structure, and its shape is very predictable.
If we start to replace one of these hydrogens with a carbon, we create something new. If we then make a double bond between the two carbons, we create yet another new molecule. And this can continue, right? We could take this carbon, remove a hydrogen, and attach another carbon, and another, and another, to the point where we create very long chains of carbon.
Alternatively, instead of forming more linear shapes, carbon can also form ring shapes. So, right, these are different carbon rings. You can see we can even incorporate things like nitrogen into a carbon ring. So carbon gives us more space, essentially, to build. It's a more interesting element when it comes to building larger macromolecules.
So because we are mostly carbon-based, we are able to become more complex, larger living things. As molecules become larger and more complex, some kind of interesting things start to happen. Because things get larger, they start to take on three-dimensional shapes, and that can affect, the three-dimensional shape can affect how the molecule behaves. This is how we get things called isomers.
Isomers are molecules with identical chemical formulas. Um, for example, here we have butane and isobutane. If you count up all of the atoms here, we have C4, four carbons, and then one, two, three, four, five, six, seven, eight, nine, ten hydrogens. So C4H10. If you were to do the same thing with isobutane, you would also get C4H10.
So just looking at the chemical formulas, you would think, oh, these are the same molecules, but they're not. Because with isobutane, instead of forming just a simple straight carbon chain, one of the carbons in the middle has a bond to two carbons instead of just one. And as a result, you get a different three-dimensional shape.
This is referred to as a structural isomer. All of the atoms are the same. but the way that the atoms are connected is different.
A geometric isomer is when all of the atoms are the same, all of the connections between the atoms are the same, but there is just a change in the orientation of the binding. So here we have cis-2-butene and trans-2-butene. The difference, and I'll get out my pen, Is with the cis model, the, you know, we have this carbon here and it's bound to a hydrogen and this is called a methyl group. With the trans model, the hydrogen and methyl group swap places.
So all the same binding, all the same atoms, but we have a different molecule because this change creates a. change in the three-dimensional shape. Anantamers are a special type of geometric isomer where the difference between the two isomers, between the two molecules, are that it's all the same atoms, it's all the same connections.
All the same connections are even like in the same orientation unlike the geometric isomers, but they form kind of a like left-hand right-hand model. If you Just take your hands, you know, without flipping them around. You can never superimpose them, right?
Your thumbs are going to stick out on either side. That's how these anantamas are. They're kind of left hand, right hand.
So they're not truly identical, although, but they're sort of like mirrored images of each other. But even this difference can create a significant change in the molecule's behavior. So in short, carbon gives us a lot of flexibility as a building block for molecules, right?
We can form lots of different bonds and we can orient those bonds differently. And as we learned on the last slide, those different orientations can create different molecular activity, which gives us just more diversity of life. And so all of these, you know, everything kind of thinking of carbon as our. building block or our kind of like skeleton what we use to build off of often what we're using to build off of the carbons the groups of atoms that are bound to these carbon skeletons are called functional groups functional groups you'll get more familiar with them just the more you're working in biology here's a pretty good table of the ones that will for the most part ones that will come up this semester Even something like sulfhydryl won't come up all that often.
Carbonyl, not as much either. But all these other ones will come up a lot in biology. And these are just groups of atoms that we see often or regularly in nature. And they always kind of give specific properties to a molecule.
For example, the hydroxyl functional group, oxygen bound to a hydrogen. This always creates polarity in a molecule because we create a dipole with this bond. Whereas methyl groups, CH3, nonpolar bonding, removes polarity from a molecule. It'll make a molecule nonpolar.
So if you ever see like a big, a large biological molecule and you're asked about its properties, you can start to look at some of the functional groups and that'll give you some indication as to how this molecule behaves. If there are lots of methyl groups, it's probably a nonpolar molecule. If there are lots of hydroxyl groups, it's probably a polar molecule.
So that will wrap up this recording and then also module one as a whole. Make sure you take the quiz that'll have questions from each of the four recordings. It says on the syllabus, but you get just till you hear you get three shots at that quiz. You know, I recommend, you know, obviously watching this recording first and then going and giving your best shot on try one. It'll just save time and you'll get more out of it than if you try to do like a guess and check method.
But yeah, the quiz should be available as soon as these recordings are. Hopefully this was a good first recording and looking forward to seeing you all in person either on Wednesday if you're in my recitation or on the following Monday if you're only in my lecture.