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Video transcript

- [Voiceover] We spent some time talking about hydrocarbons and hydrocarbons are interesting especially if you want to combust things, if you want some fuel, but now we're going to make things a little bit more interesting by adding things to the hydrocarbons and the things we're gonna add we call functional groups. Functional groups. And my goal in my video is to give you an overview of the major functional groups that you might see attached to carbon backbones that make the molecules interesting biologically. Now, the first one I will focus on is an OH group. So, we have an OH attached to a carbon backbone over here. It doesn't have to be attached to a carbon backbone but the OH right over here, this is called a hydroxyl group. Hy, hydroxyl group, and when it is attached to a carbon backbone like this one is then it turns the entire molecule into an alcohol. Alcohol. This an alcohol. And this one in particular if you want the name we have two carbons on the longest, longest chain and it is an alcohol so we use the prefix Eth for the two carbons. So, let me write that down. We're going to use the prefix Eth because we have two carbons here. And we're gonna say Ethanol. Now, what are the properties here? Well, you have oxygen which is very electronegative bonded to a hydrogen and to a carbon but the oxygen is a lot more electronegative than the hydrogen so you're going to have a partially negative charge at this end away from the hydrogen. A partial positive charge at the hydrogen and to a lesser degree the carbon end too but hydrogen is even less, is a less electronegative than even carbon. And this one, so, a hydroxyl group they are polar, they are polar, and because they are polar you can dissolve them into water. They are hydrophilic. They can form hydrogen bonds so that you can dissolve this. Now, similar, a similar functional group or one that has somewhat similar properties is right over here. And you might say, "Wait, why is this one similar? "I have sulfur here instead of oxygen." But if you look at the periodic table you will see that sulfur and oxygen both have six valence electrons. They both would love nothing more than to grab or pretend to grab two other electrons and this is why they form, they tend to form two covalent bonds. And so, this group right over here, which is called a sulfhydryl group. This is a sulf.... Sulfhydryl. Sulfhydryl group. It's kind of similar to a hydroxyl group with the one difference, with the one difference that sulfur is electronegative but it is less electronegative than oxygen. So, you're still gonna have a partially negative charge and a partially positive charge, but it's going to be less polar. So, it's not quite as polar as if you had a hydroxyl group. Now, when you have this sulfhydryl group it's attached to, say, a carbon chain and when I use this R right over here, when I have this R. This is just shorthand for carbon and a bunch of other stuff. I could've, if I wanted to generalize an alcohol right over here I could've written R and then I could've written the hydroxyl group. O and then bond that, bond that to an H. So, over here the shorthand R would have been the shorthand for all of... The R would've been the shorthand for all of this business. All of this business right over here. And so that's what we're doing over there. I'm not saying that this R is exactly this. It means that some carbon backbone and some carbons, hydrogens, and maybe other stuff, maybe even some other functional groups, but we're just focused on the sulfhydryl right over here. And so if you see something like this, you'd say "Okay, yeah, this is still going to be polar, "but not quite as polar as if I were dealing "with a hydroxyl group." Now over here we have a more complex molecule, but this is a molecule that you run into probably on a daily basis. This is the sugar fructose. This is the sugar fructose. And this is when it is not in a ring. If you were to throw this into-- If you were to throw this into water, it'll readily form a ring, but when it is not in a ring form you can recognize already the hydroxyl groups. You have a hydroxyl group on this carbon. You have a hydroxyl group on this carbon. Hydroxyl group on this carbon. You have a hydroxyl group on that carbon. You have a hydroxyl group on this carbon. And then, on this carbon, it's double bonded to an oxygen. We call this a carbonyl group. So this is a carbonyl. Carbonyl. Carbonyl group. Now this is actually how you would tell a sugar, it's like, look, especially when it's in a straight chain, all my carbons have one hydroxyl on them except for this one, it has a carbonyl group. And one of the take aways for a carbonyl group, we've already talked about oxygen being very electronegative, even more electronegative than carbon, it's double bonds, it's going to hog the electrons on the oxygen end, so you're going to have a partially negative charge. Partially negative charge over here, partially positive charge over here, and so this, this one is also going to be polar. And then, in fact, the entire molecule is very polar because it has all these hydroxyl groups on it as well, but this is also going to give it polarity here and, because this carbon has a slightly positive charge, it is susceptible to nucleophilic attack, and when you take organic chemistry, you'll see that things that want to share-- That have a predisposition to share their electrons in a bond might want to come and form a bond with this carbon and maybe one of these electron pairs go back to this oxygen and maybe bond with something else, but we'll talk about it in the future when we study some organic chemistry mechanisms. The important thing here is just recognize, "Okay, I've got some hydroxyl groups? "Okay, I've got a carbonyl group right over here as well." Now this molecule, this is an amino acid, and you will see amino acids a lot when you study biology. And this has actually a couple of interesting groups on it. The first group of note is this stuff that I am circling in orange because you have a carbon that, you could say it's part of a carbonyl group, but it is also bound to a hydroxyl group. It is also bound to a hydroxyl group right over there. And when you have this configuration where you have a carbon bond double-bonded to an oxygen and then single-bonded to a hydroxyl group, we call this a carboxyl group. This is a carboxyl. Carboxyl, carboxyl group. And one of the take aways from this is that it is acidic because this can readily give up the hydrogen proton. This oxygen, we already know oxygen likes to hog electrons, it can take up both of these electrons and become negative, and actually, there's actually resonance here because those electrons get shared throughout the group and actually even potentially even beyond the group but especially inside of the group, then leaving the hydrogen proton. So this can readily donate a hydrogen proton... This can readily donate a hydrogen proton, so this is generally viewed as acidic. Acidic. Now, this amino acid over here, it also, and this is where this name comes from, actually the acid comes from this carboxyl group, this is the acidic part, and then you have an animo group. You have an amino group right, right over here. And because it's involving a nitrogen, this is the amino group. This is what gives the amino part of the name amino acid. Amino acid. And this actually is generally basic. Because nitogen could-- It has a lone pair. It has a lone pair of electrons right over here. And so it could use that lone pair to pick up, to form a bond with a hydrogen ion, to pick up a hydrogen ion. So, under the right circumstances, it can form a bond with a hydrogen ion, which, we know, a positive ion, which would just be a proton, and so it would have a positive charge. And so since it can sop up hydrogen ions, we can view this, the amino group, as being basic. But this right over here is leucine, it's an amino acid super important for muscle growth, but there you can appreciate. You have essentially a hydrocarbon chain, but it has a carboxyl group at this end and an animo group right over here. And another thing that you'll sometimes people talk about is even hydrocarbon groups. For example, if you consider the main chain of this, and we could consider to either using this carbon or this carbon, but if we consider this to be the main chain of carbons, if we consider that to be the main chain of carbons, then we would consider this right over here to be a methyl group. Remember, the prefix "meth" refers to one carbon, so it's one carbon bonded to a bunch of hydrogens, to three hydrogens here, and so we would call this a methyl group. And in general, if you have a hydrocarbon bonded to other hydrocarbon groups, these things are hydrophobic. So these things, there's nothing polar about them, and so they're not going to want to, at least these parts of the molecule are not going to naturally dissolve inside of water. Now the last group we're going to focus on, and you're going to see a lot of these, and especially in biology, you're going to see this as a part of ATP, you're going to see it's the backbone of DNA, and that's phosphate groups. And this right over here, this right over here is the phosphate group. I've drawn it bonded to a bunch of, kind of a group over here, who knows what it is, bunch of carbons, a bunch of other things, and then I've bonded it to two hydrogens, but it doesn't always have to be bound to hydrogens. But when it is bound to hydrogens like this, it's considered to be protonated, and so it can actually take up, it can actually hog these electrons and dump these hydrogens, and dump these hydrogens into a solution. So a phosphate group is considered to be acidic. It is considered as well, especially when it is protonated like this, it is considered to be acidic because it can donate protons. So this is just an overview of a lot of the functional groups you will see throughout biology and a lot of big, hairy complex molecules, when you actually break it down, you say, "Okay, there's a hydrocarbon chain there. "Oh, I see a sugar there! "I see a bunch of hydroxyls, and I have a carbonyl group. "Oh, I see an amine group, I see-- "Or, amino group. "I see a carboxyl group." You can think about this going to be acidic? Is it going to be polar? Or do different parts of the molecule have different functions?
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