We've 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 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 this 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 you 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 ...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 is an alcohol and this one in particular, if
you want the name, we have two carbons all along its longest chain and it is an
alcohol so we use a prefix eth- for the two carbons, so let me write that down. We're
gonna use the prefix eth- because we have two carbons here and we're gonna say
"eth"-anol, ethanol, which you might more commonly know as rubbing, as rubbing
alcohol. Now what are the properties here? Well you have an 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 end and, to a lesser degree, at the carbon end too, but hydrogen
is even less electronegative than even carbon. And so
this one, so a hydroxyl group, they are polar, they are polar, and because they're
polar you can dissolve them into water. They are hydrophilic they can form
hydrogen bonds so you can dissolve this. Now a 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
tend to form two covalent bonds. And so this group right over here,
which is called a sulfhydryl group. This is a 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 have, if I wanted to generalize an alcohol right
over here I could have written R and then I could have written the hydroxyl
group O and then bond that to an H so over here this shorthand R would
have been the shorthand for all of, the R would have 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 it's some, you know,
carbon backbone and 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 gonna 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 throw this into water it'll readily form
a ring but when it's 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, this is a
carbonyl...carbonyl group and this is
actually how you would tell a sugar is like it 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 takeaways 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 gonna have a partial, you're gonna have a partially
negative charge, partially negative charge over here, partially positive
charge over here, and so this one is also going to be polar, and 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,
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, go back to this oxygen
and maybe bond with something else. But we'll talk about that in the future when
we study some organic chemistry mechanisms. The important thing here is
just recognize, okay I got some hydroxyl groups, hey I 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 is, you could say it's part
of a carbonyl group, but it is also, 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 group and one of the takeaways 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, this can readily donate a hydrogen proton so this is
generally viewed as 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, that's the acidic part, and then you have an amino group,
you have an amino group right over here because it's involving nitrogen.
This is the amino group. This is what gives the amino part of the name "amino acid",
Amino acid. And this is actually generally basic because nitrogen could,
it has a lone pair, it has a, 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 as, 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 amino 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 it 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. Rremember 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 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 molecules, 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 it as part of ATP. You're going to see it as 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, a 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
pro-, it's 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 is this going to be
acidic, is it going to be polar, or do different parts of the molecules have
different functions