Hi. It's Mr. Andersen and this is chemistry essentials video 56. It's on biological and
polymer systems. If we were to look inside your blood we would find that it's filled
with hemoglobin. And that hemoglobin is made in a ribosome. And it looks just like this
when it comes out. What we have are a series of amino acids that are attached together
through covalent bonds. And the amino acids themselves are held together with covalent
bonds. But it comes out real linear like this. The moment it comes out of the ribosome however,
intermolecular forces take over. So hydrogen bonds are going to weave this into an alpha
helix or a beta pleated sheet. These alpha helixes and beta pleated sheets then are going
to fold on top of each other where we have hydrophobic regions moving to the inside.
Hydrophilic on the outside. We have all these dispersion forces that are holding different
parts of that molecule together. And so eventually we're going to have this multipolypeptide
protein form that does its specific job. And so it's not just the covalent bonds that are
important. It's going to be these non-covalent interactions. And so in a big molecule the
structure, in other words how it's put together, is going to fit its function. What it does.
If the structure is not correct, then the function is not going to be correct as well.
That structure is made up of covalent bonds holding that molecule together. But we also
have all these intermolecular interactions. These non-covalent interactions. Things like
hydrogen bonds. Things like dispersion forces. And all of these are going to work together
to give it that specific structure to do a job. So for example an enzyme has to have
that perfect shape so the substrate can fit exactly in it and we can break that down.
Now as we start to make polymers of our own it's important that we understand how their
structure fits their function as well. And so a lot of these biomolecules are polymers.
What that means is they're made up of a number of different monomers just like this word
is made up of letters. And so let me show you an example of a monomer. So this monomer
right here, we have ethylene terephthalate. What's going to be the polymer if we attach
this together? That's going to be polyester, like a nice polyester leisure suit. Or if
we were to take this monomer, glucose and we were to put that together in a polymer
what would we get? We would get a polysaccharide, like starch. Or if we were to take this amino
acid, that monomer, and we were to attach it together what would we get? We would be
a polypeptide. So we're going to get this massive protein. But what's holding it together
is going to be all these intermolecular forces between different parts of the molecule itself.
So when we look at a molecule like DNA what we're really seeing are the covalent bonds
between all of those atoms that give us this structure. But what you don't see are all
those non-covalent interactions. And so let me put some of those in with stars here. We're
going to have all those hydrogen bonds in the middle that hold those two helixes together.
And then we're going to have those hydrogen bonds on the outside that give it the stable
double helix kind of a structure. And so again, if we don't have both covalent and non-covalent
interactions, we're not going to have a molecule that works. Likewise if we were to take this
simple polypeptide as all these amino acids come out and just look at the covalent bonds,
it doesn't give us that structure of that overall protein. And again that structure
of that protein is incredibly important. So if we're looking at a biological molecule,
like an enzyme, which is simply a catalyst, which is made of a protein, how does that
work? We're going to have an active site where the substrate will fit in. And so that substrate
will fit in. And then it's going to kind of hug it. We're going to have this induced fit
where the molecule is going to interact with that substrate. And as it does, it's putting
tension on it. And then it's going to break it apart. It's going to lower that activation
energy. And so if we don't have the correct structure, if we don't have these intermolecular
forces between the enzyme and the substrate, it's simply not going to work. Now as we start
to create polymers of our own, if we understand how their structure fits their function then
we can start to design polymers that do wonderful jobs. So for example teflon, the structure
of teflon, which is going to be a polymer gives us its function which is going to be
that nice non-stick pan. Of if we were to look at kevlar for example, its structure
is going to give us that rigid function that's going to create that protective helmet or
that kevlar vest. Or if we were to look at nylon. If you look at nylon right here, these
are all going to be intermolecular forces between adjacent strands of the nylon. And
so that's going to give us its function as well. So did you learn to identify both the
covalent and non-covalent interactions? I hope so. And I hope that was helpful.