So now let's talk about the structure of DNA and the structure of RNA.
This would be RNA on one side. And this would be DNA on the other. The one thing that jumps
out is that RNA is a single helix. And DNA is a double helix. But if we look at the structure
of both of these, which are called nucleic acids, they're mostly made up of just three
parts. And so both of them have, let me get a color that works, both of them have a sugar.
In RNA that sugar is going to be ribose sugar. In DNA it's going to be deoxyribose sugar.
They then have a phosphate group. And then they have bases on the inside. And so if we
look at this would be RNA right here. On RNA you have a phosphate attached to a ribose
sugar attached to a phosphate attached to a ribose sugar attached to phosphate ribose
sugar phosphate ribose sugar. And so the backbone which on here would be this kind of greenish
part that goes down here, is simply a phosphate attached to a sugar attached to a phosphate
attached to a sugar. That's relatively boring. It's the same all the way down. Now if it's
DNA it's going to have a deoxyribose attached to a phosphate deoxyribose. And it's going
to be the same side on both sides of that backbone. What goes off the inside, attached
to the sugars is going to be the base or the nitrogenous base. And so in RNA, it's adenine,
guanine, uracil and cytosine. So you've got cytosine, guanine, adenine and uracil. If
you look at DNA the bases that we have are cytosine, guanine, adenine and thymine. And
so this is another difference between the two. In RNA it's going to be a uracil. In
DNA it's going to be thymine. But if you look at the structure of those two chemicals it's
almost identical. And so they serve the same purpose. DNA is simply a double helix. So
it's going to have bases on either side. And so if we have an A on this side, then we'll
have a T on the other side. Okay. Next I want to talk about DNA replication. When does DNA
have to replicate itself? Well every time a cell makes a copy of itself, in other words
every time you go from cell one and let's call that the zygote to two stem cells, we
have to duplicate the DNA inside there. In other words every cell in your body has the
same exact DNA as that first cell. And so how does DNA copy itself? Well Watson and
Crick actually suggested, since you have a double helix, and so this is the original
strand of DNA on this side. Since it's a double helix what you can simply do is unzip it in
the middle. If you unzip it in the middle then we can build a new strand on the this
side. A new strand on this side and now you have two strands of DNA. So we have one strand
of DNA to start. And then we have two strands of DNA when we're done. That one and that
one. Now the machinery of how it works is a little funky. You can only add new letters
on the 3 prime end. And so on one side the DNA polymerase which is an enzyme that simply
adds new bases or new nucleotides to the other side of the DNA, it'll run really smooth on
this side which is called the leading strand. On the other side it kind of has to back stitch
or work in the opposite direction. But essentially what you have is when you're done it's unzipped
and now we have two new strands of DNA. And they're identical to that first strand. And
so then that DNA is split into each of the cells as we go through the cell cycle. Next
I want to talk about central dogma. So after they figure out the structure of DNA, mostly
Francis Crick goes on and he actually coins this term the central dogma. He then wants
to figure out well, how does DNA actually make us? It's the secret of life how does
it actually make us? Well the central dogma explains how DNA makes RNA. And that process
is called transcription. RNA will then make proteins. The proteins make the phenotypes.
And the phenotypes eventually make you. And so the central dogma explains how we can go
from DNA to actually you. The first step is going to be called transcription. I always
remember the script means to write. And so what we have is we have our DNA. So this is
going to be our DNA right here. This is going to be a gene. So it's a portion that we actually
want to make a protein out of. There's an enzyme called RNA polymerase. So what RNA
polymerase, just like DNA polymerase is going to do, is it's going to drive down the DNA.
So RNA polymerase will drive down the DNA. And as it does that it make a copy behind
itself. And that copy is going to be messenger RNA. So if we go again, after RNA polymerase
is done and it leaves, we now have messenger RNA. And so we started with DNA. That's going
to be this double strand right here. But after RNA polymerase has gone by, we now have messenger
RNA. Or there's a message. Now the DNA right here will stay within the nucleus. And so
the DNA is protected. It's like the master code inside the nucleus. It will never leave
the nucleus. But the RNA is free to leave the nucleus. And actually make proteins. Or
make things. Okay. How does it make things? Well that RNA is going to move out into the
cytoplasm. So here's our RNA. It's this long stretch. And so what it'll do is it'll feed
through something called the ribosome. So this big big green structure is going to be
called a ribosome. Every three letters of the RNA is going to match on three letters
of a tRNA. That's what this is. It's a different type of RNA. It's called transfer RNA. And
that transfer RNA is going to bring in one amino acid. Amino acids are the building blocks
of proteins. And so what'll happen is that amino acid will attach on to the string of
all the other amino acids in this protein. And then everything shifts over. So now we'll
have the next one come in. And the next one come in. And the next one come in. And so
what do we do here? Well we're going from RNA. In this case it's the messenger RNA.
And what we're going to end up with right here is going to be a protein. Oops. Let me
right that more correctly. A protein is going to be what you're made up of. So when you
look at my hair or the keratin of the color of my eyes, those are all proteins. And the
proteins are actually made by the ribosomes and those are actually made in the cytoplasm.
So now we've gone from the message of the DNA to the message of the RNA. And now we've
translated that into a protein. So translation is moving the messenger RNA actually into
a protein. So what do the proteins create? Proteins eventually create phenotypes. And
so phenotypes are going to be what you physically look like. And so remember when we talked
about evolution, the peppered moth in general will look like this. It's going to be this
white appearance. But if you add one gene to that or one mutation, what you'll get is
this appearance. In other words just by changing the gene a little bit, we can get this huge
phenotype. That phenotype change is going to be the physical characteristic that you
have. And so this is how DNA and changes to the DNA will eventually create changes in
the messenger RNA. Which eventually create changes in the proteins. Which eventually
create changes in the phenotypes. So the phenotype is what you physically look like. So any kind
of a change in the DNA can have changes in our physical characteristic which then is
selected for or against in the environment. Now Richard Dawkins who writes a lot on the
idea of a selfish gene and how genes are actually the units that are actually being selected
for, has coined this term which I like. It's called the extended phenotype. In other words,
a beaver has a number of different phenotypes. It has a bunch of number of different physical
characteristics. Like the flattened tail. The big teeth. Tiny little arms. These are
all created by DNA. But what else do beaver's produce? Well they might produce a beaver
dam or a beaver lodge. Is that a phenotype? Is it actually made by genes? No. But it's
an extension of genes. In other words, does this allow a beaver to survive or not? For
sure it does. And so it's also going to be selected by natural selection as well. So
not only the physical characteristics that you have but that behavior that you have can
be selected for as well. Last thing I want to talk about is genetic engineering. And
so going way back to the Frederick Griffith experiment, what we found is bacteria can
actually share genetic information. They can share these little plasmids. And those plasmids
or that auxiliary DNA can actually give them a new trait, like the ability to be virulent
in the Fredrick Griffith experiment. But what scientists have figured out is since DNA is
interchangeable, since we can take DNA from a human, we can cut that out and we can insert
it into a bacteria, it'll work perfectly. And so what scientists have done is they've
actually inserted genes from humans into the plasmid of bacteria and the bacteria can make
copies. And they can actually make proteins. And so most all of the insulin that is made
today is made not by gathering it from animals or growing it in animals or using cadavers
was what they used to do. They're actually having bacteria, with the genes of the humans
inside it to grow the insulin. And they've actually figured out now that you can actually
insert the genes for insulin into safflower. And so we'll be able to grow proteins, human
proteins, in plants which makes it really really cost effective and available to all
the growing number of diabetics that we have today. So that's DNA. That's RNA. And I hope
that's helpful.