Hey folks, this is going to be our second screencast on the big four molecules, and
this time we're going to talk about proteins and nucleic acids. So when we talked
about carbohydrates and lipids, we mostly used carbon hydrogen oxygen and nitrogen,
but today we're going to add phosphorus and sulfur into the mix as we create our
two other kinds of biomolecules. Let's begin with nucleic acids. So the point of
nucleic acids is to transfer genetic information from parent to offspring or
from one generation to the next, and the two that you're most familiar with are
probably DNA and RNA. Now, usually we find nucleic acids in the nucleus of the cell
which is also sometimes called the control center of the cell, but sometimes
we find them out in the cytoplasm as well. DNA has a characteristic
double-helix shape which looks a lot like a twisted ladder and it's made up
of several different components. It's made up of sugars and phosphates, and that's
where we're going to see that phosphorus that we talked about on one of our first
slides, and then it's also made up of four different varieties of nitrogenous
bases that make up some of the rungs of the ladder. We're going to take a
look at those.
So, if we were to zoom in on this boxed area of the cartoon of DNA,
this is what it would look like at the molecular level. You have several
different components; so in this teal color right here, we have the
phosphate group that's made up of phosphorus bound to four oxygen molecules,
and then we have a pentagonal sugar.
This right here is called ribose; you can see that it's got one, two, three, four
five points. And then we also have this part right here and this is going to be
the most important part of the DNA.
This is called the nitrogen base; there are four different varieties and they
pair together in a very specific way. DNA and RNA are shaped pretty differently
from one another; they both have the same components in terms of their
phosphate sugar backbone, but they have different numbers of strands. DNA has
two strands that are complementary to one another, so they pair together, and
then RNA has only one strand but both of them are made up of the same
components. In DNA adenine always pairs with thymine, and cytosine always pairs
with guanine. So A and T and C and G. And the order and combination of base pairs
determines what we call the genetic makeup of an organism. A chunk of the DNA
double helix is often called a gene, and the gene is the base pair combination
that results in a specific trait. So if you have one combination of base pairs
you might end up with red hair, if you had a different combination of base
pairs, you might end up with blonde hair. The way that this works is DNA is
essentially a set of instructions for how to build certain proteins.
Depending on the base pairs that you have, you might have the instructions for
building black hair proteins, or you might have the combination of base pairs
that codes for building brown hair proteins. The DNA base pairs that you
have are a hybrid of your mother and father's DNA.
This is why you oftentimes look a lot like your parents. The human body does
make mistakes, though, and so sometimes you wind up with what's called a
mutation in your DNA, so you don't have an exact copy of what your mother or
father has. Now let's move on to proteins. Proteins have a huge variety of
different shapes, sizes, and jobs in the body, and there are a lot of different
examples, but here just a few. We have proteins that are called enzymes, we
have structure proteins that help us to build the solid parts of our body, we
have storage proteins, and then we also have hormonal proteins that work on
signaling, but the point here is that every single one of these different
types of proteins is going to be an enormous molecule and it's going to have
a very specific shape and size. Without that specific shape and size, it could
never do its job now let's talk protein structure. So, no matter what kind of
protein you're creating, you're going to make it out of a combination of 20
different amino acids. You might have a lot of one kind and just a few of another,
but there are 20 different varieties of amino acid building blocks.
Let's imagine that each one of these different colored squares is a different
amino acid. We only have six different varieties here, but remember
that there are actually 20 different kinds of amino acids. I'm now going to
connect each of these amino acids to the ones on either side of it.
Amino acids are bound together by a bond with an oxygen in the middle of the two
of them. So, we have to bond with an oxygen in the center that connects each
amino acid. This type of connection is called dehydration synthesis, and every
connection that you make will produce one molecule of water. So, here's my water
and it's going to involve two hydrogens and an oxygen, which together make up
molecule of water. This connection process, if I were to connect all six of these
amino acids, would produce a series of water molecules. After I connected all of
these, I would have produced a total of six molecules of water, and as a result
I've produced this long chain of amino acids. Now this chain right here has a
name; it's called a polypeptide and the reason that it's called a polypeptide is
because each of these bonds that are in between the amino acids are actually
called peptide bonds. This chain, however, is not a protein yet, it's still only
called a polypeptide. The polypeptide chain has to be folded and packaged in
the golgi apparatus until it achieves a perfect shape. Until it achieves its
perfect shape, it won't be able to perform its job as a protein. Let's
just do a quick recap of this; the building blocks of proteins are called
amino acids, there's 20 different varieties, and we have to string them
together into a long chain using peptide bonds. We call this a polypeptide, but
this isn't a protein yet, we have to fold it into exactly the right shape for it
to actually be a protein, no matter what the protein's job is ultimately going to
be. We fold it in the golgi apparatus
and then finally we have a protein.