Nucleic Acids


Uploaded by bozemanbiology on 12.11.2012

Transcript:



Hi. It's Mr. Andersen and in this podcast I'm going to talk about nucleic
acids. When I talk to students about nucleic acids, they're confused. They don't know what
they do and they don't usually know what they're made up of. They do know that they're DNA
and RNA but let's start with what they do. And so the biggest job the DNA and RNA have
is making the proteins. The proteins inside the cell. And so when you look at me, you're
looking at the proteins, but where are the directions to make those proteins? Those are
found in the DNA. And how do they get to the proteins? Well they're shuttled out by RNA.
And RNA is more of a worker that's making these proteins inside the ribosome. And so
the first job they have is making proteins. What's the second thing they do? Well they
make up our genes. And so that's what we pass on to the next generation. And so this is
my son. He contains half of the DNA that I do. So I gave him a random half of my DNA.
And my wife did the same. So he's a combination of me and my wife. And life has just passed
DNA down generation after generation after generation. We've never found life on our
planet that doesn't have DNA. That means that we're all connected through this single thread
back to that first universal common ancestor. But what are they made up of? Those are nucleotides.
And so these are the building blocks of DNA and the building blocks of RNA. So let's look
specifically at one. So this is one nucleotide right here. A nucleotide is made up of three
parts. We've got a phosphate group, that's going to be pictured right here. It's a phosphorus
in the middle and then oxygen around the outside. Phosphate groups are really famous in biology.
So they're the phosphates that are found in phospholipids that make the cell membranes
of all life. And it's the same phosphate that we're going to find in ATP, adenosine triphosphate.
It's the energy source. And in fact the adenosine triphosphate is exactly the same adenosine
triphosphate that we add to make DNA. We'll get to that in just a second. What else do
we have? Well, we have a pentosugar. Pentosugar means we have a five carbon sugar. In DNA
that's going to be a deoxyribo sugar and then in RNA it's going to be a ribosugar. And then
the most interesting part of a nucleotide is going to be the nitrogenous base. And it's
called a nitrogenous base because it has nitrogen. And so most things in life are made up of
carbon but there's going to be a lot of nitrogen here in the base of this nucleotide. And this
is going to be different in each nucleotide. And so let's take a look at the nucleotides
found in DNA. And so basically you have adenine, cytosine, guanine and thymine. And so we have
four different bases and therefore we have four different nucleotides. And you can just
see looking at them the size is going to be a little different on all four of these. In
RNA they don't have thymine, you might notice. But they have uracil. It's going to look a
lot like thymine but it's not going to be thymine. If we were to now look at all of
those nucleotides together, so A, C, G, and T. And that's where the names come from. In
DNA we're talking about these nitrogenous bases or these nucleotides. Now we've got
uracil. Basically if we put them in order by their size we've got two major groups.
We have these ones that have two rings and we call these purines. So this is adenine
and this is going to be guanine. And then we have the pyrimidines and there just going
to have one ring. So cytosine, thymine and uracil are all going to have one ring. So
they're going to be smaller. And that'll become really important when we start bonding them
together. So let's talk about bonding. How do you connect them together? Well when we
talked about carbohydrates there's really only one way to connect carbohydrates. Or
when we talk about amino acids, there's really only one way to connect them, but especially
when we get to DNA you can connect nucleotides in two ways. So let's start with way one.
Way one, we could put this one right underneath it so we've got an adenine and a guanine and
then through a dehydration reaction we could lose a H2O right here and we could form a
covalent bond between two nucleotides. And so if we were to add another one, we would
add another nucleotide here, we'd lose a water and we're going to make another covalent bond.
And so we can attach them together like that. And so that's what RNA is. RNA is a number
of nucleotides simply in a row and they're connected with covalent bonds between each
one. There's another way however when we get to DNA that we can bond them. And so let's
say we have these two nucleotides, adenine and guanine, how could I attach this thymine
right here? Well basically I can turn it upside down and it's going to form hydrogen bonds
here between the adenine and thymine. And you've probably heard this before that adenine
will always bond to thymine and guanine will always bond to cytosine. And that's why. There's
going to be interactions between the oxygen, nitrogen and the hydrogen and make these hydrogen
bonds that are connected with the two. And so when you're looking at DNA, let's kind
of switch to this next slide. When you're looking at DNA, that's what's being connected
right here in the middle. So that's going to be the hydrogen bonds between the nitrogenous
bases on either side. And so why do we have DNA? Well we think life started with RNA because
it contains a message, but overtime we kind of had two RNAs wrap around each other and
we eventually had DNA. There's more to it that that, but DNA is going to be a more stable
structure. We're going to have those hydrogen bonds here and then we're going to have covalent
bonds between different backbones of the DNA as well. And so what are the backbone of DNA
really made up of? It's just a sugar attached to phosphate to a sugar to a phosphate to
a sugar. And so what are some differences between DNA on the right and RNA on the left?
Well the first one would be the uracil versus the thymine. So that's going to be a different
nitrogenous base. DNA is going to be a double helix and RNA is going to be a single helix.
And then in life DNA is going to be found in the nucleus and RNA is going to be found
pretty much everywhere that we need it. So if you're confused on how we go from DNA to
proteins, or if you're really interested in the whole secret of life I'll put a little
link to a video I made that kind of talks you through how we go from DNA to proteins.
But the last thing I wanted to leave you with is how important they are. If you're interested
in RNA and if you're interested in science and video games, then you may want to check
this out. This is eterna. Eterna is a video game. I think it's centered at Stanford University
and basically what they're doing is they're letting people on the internet build sections
of RNA. And so basically you build sections of RNA. They have competitions each week and
basically the winners each week, they will make your RNA. So they'll actually synthesize
and make your section of RNA and then they'll see how it does. And so I'm going to launch
the video game and talk you through the first level. And if you're interested in RNA or
making things real in biochemistry you may want to give this a shot. So here's level
one. Basically it's a tutorial so I can click on next and it will talk me through what I'm
going to do. So you're going to build your own RNA. Let me click on the next one. The
RNA is made up of four bases. Hopefully you know what that means now. Yellow base is adenine.
Guanine, uracil and cytosine. And so as a warm up drill let's convert all the bases
to guanine. So let me click here to start. So basically what you can do is go down here.
I'm going to get my mutate and I'm going to mutate this to guanine. I love the music in
here or the little sounds effects. Nice. So I cleared level 1. And then you can go to
the next puzzle and we can just, going through, and so basically on this one what you can
do is they will attract each other. So for example they're going to say that adenine
and uracil are going to come together and that guanine and cytosine are going to come
together. And so basically what you do is you get to play around with pairing these.
And so I'm going to stop playing the video game in front of you, but give it a look.
It's a really cool idea. People competing to make RNA and then they're actually building
it in the real world. And so that's nucleic acid. It's incredibly important and I hope
that's helpful.