Proteins and Nucleic Acids

Proteins and Nucleic Acids


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.